27 Sep
2001
27 Sep
'01
12:32 p.m.
Hi again folks,
My US 8032 turned up today (yay!). Since I can't modify the transformer
(unfortunately - it looks like the US one doesn't have dual primary taps
like the UK one), I've swapped it out with the 240vac transformer from my
other (still broken) 8032.
This machine has a wobbly screen, just like the 8032-SK (which was broken,
but I installed the working motherboard), the other 8032 (which was
working, until I swapped the broken m/b), and the 3016. In fact, the only
PET I've got which *doesn't* have a wobbly screen is the 2001. Well, it
does wobble, but only a tiny bit.
ISTR a discussion (mostly with Tony) about dried electrolytics maybe
causing the problem. However, I spoke to the chap in the US who said that
when the 8032 left America it had a rock-steady screen... Since I left the
big cap in place, it can only be the transformer which is causing the
wobble - can't it?
I genuinely don't know. That's the only part I've swapped in the new 8032.
Could a flakey transformer be making the screen wobble? How do transformers
go flakey anyway, if indeed they *can* co flakey? Or is the US chap telling
porkies?
Thanks, again, in advance.
--
Cheers, Ade.
Be where it's at, B-Racing!
http://b-racing.co.uk
27 Sep
27 Sep
1:17 p.m.
-> Since I left the big cap in place, it can only be the transformer
-> which is causing the wobble - can't it?
->
-> I genuinely don't know. That's the only part I've swapped in the
-> new 8032.
-> Could a flakey transformer be making the screen wobble? How do
-> transformers go flakey anyway, if indeed they *can* co flakey?
Well, actually I think the transformer is the cause of the problem, but not
in the way you are thinking. You may have an problem with the magnetic
field of the transformer being coupled to the monitor, either via the yoke
or directly to the CRT. Does the problem lessen as the distance between the
transformer and the monitor is increased?
See the photos of the Commodore Educator 64, Model 4064 at
http://www.swtpc.com/commodor.htm . I remember the general position of the
power transformer is similar to the Pets. Note the shielding of the
transformer in the photos. This was used to prevent the problem which you
are describing, and if this shielding is removed the wobble will occur. Try
placing a shaded pole motor or large transformer anywhere near the sides or
back of a modern monitor and you'll see the same wobbling effect.
Hope this helps.
Bill
5:17 p.m.
On Thu, 27 Sep 2001, Bill Dawson wrote:
-> Since I left the big cap in place, it can only
be the transformer
-> which is causing the wobble - can't it?
->
-> I genuinely don't know. That's the only part I've swapped in the
-> new 8032.
-> Could a flakey transformer be making the screen wobble? How do
-> transformers go flakey anyway, if indeed they *can* co flakey?
Well, actually I think the transformer is the cause of the problem, but not
in the way you are thinking. You may have an problem with the magnetic
field of the transformer being coupled to the monitor, either via the yoke
or directly to the CRT. Does the problem lessen as the distance between the
transformer and the monitor is increased?
See the photos of the Commodore Educator 64, Model 4064 at
http://www.swtpc.com/commodor.htm . I remember the general position of the
power transformer is similar to the Pets. Note the shielding of the
transformer in the photos. This was used to prevent the problem which you
are describing, and if this shielding is removed the wobble will occur. Try
placing a shaded pole motor or large transformer anywhere near the sides or
back of a modern monitor and you'll see the same wobbling effect.
Hope this helps.
Bill
Would it not also be true that rectifying 50Hz AC would require better
filtering than rectifying 60Hz? Hair splitting perhaps, but....
- don
10:01 p.m.
At 02:17 28/09/2001, Bill Dawson wrote:
-> Since I left the big cap in place, it can only be
the transformer
-> which is causing the wobble - can't it?
->
-> I genuinely don't know. That's the only part I've swapped in the
-> new 8032.
-> Could a flakey transformer be making the screen wobble? How do
-> transformers go flakey anyway, if indeed they *can* co flakey?
Well, actually I think the transformer is the cause of the problem, but not
in the way you are thinking. You may have an problem with the magnetic
field of the transformer being coupled to the monitor, either via the yoke
or directly to the CRT. Does the problem lessen as the distance between the
transformer and the monitor is increased?
I don't know - to try that I'd have to disassemble the whole thing again :(
The earth wires are a bit too short to make testing that easy.
See the photos of the Commodore Educator 64, Model 4064
at
http://www.swtpc.com/commodor.htm . I remember the general position of the
power transformer is similar to the Pets. Note the shielding of the
transformer in the photos. This was used to prevent the problem which you
are describing, and if this shielding is removed the wobble will occur. Try
placing a shaded pole motor or large transformer anywhere near the sides or
back of a modern monitor and you'll see the same wobbling effect.
Interestingly, the US transformer is of a different design to the UK one;
I'm assuming the primary windings are inside the secondary, and there's a
broad metal band strapped around the whole thing. The UK transformer has
the primary & secondary windings next to each other, and there's no
shielding at all. If I fabricate a box, I assume it'll have to be earthed,
and surround the whole transformer? Also, will any metal do, or does it
need to be ferric?
--
Cheers, Ade.
Be where it's at, B-Racing!
http://b-racing.co.uk
28 Sep
28 Sep
12:47 p.m.
See the photos of the Commodore Educator 64, Model 4064
at
http://www.swtpc.com/commodor.htm . I remember the general position of the
power transformer is similar to the Pets. Note the shielding of the
transformer in the photos. This was used to prevent the problem which you
are describing, and if this shielding is removed the wobble will occur. Try
placing a shaded pole motor or large transformer anywhere near the sides or
back of a modern monitor and you'll see the same wobbling effect.
When did the PETs start using all the shielding? My 2001-16N
has none of the shielding your Educator64 shows. Transformer,
mainboard and even the keyboard are all bare. While looking at the
shielding, I powered mine up for the first time since I moved about a
year ago and now it's screen shape is distorted and it shows evenly
spaced vertical bars all the way across.
Jeff
--
Home of the TRS-80 Model 2000 FAQ File
http://www.cchaven.com
http://www.geocities.com/siliconvalley/lakes/6757
27 Sep
27 Sep
1:34 p.m.
New subject: Free for Cost of Shipping - Vintage Telephone Switching Books
I have, for the cost of shipping (I'm guessing $5), two books that may be of
interest to folks interested in old telephone switching:
A Survey of Telephone Transmission - Pacific Telephone - 1956
Switching Systems - AT&T - 1961
These are cool books for your inner phone phreak.
Both books are in excellent condition. The first is soft cover, plastic
bound. The second is hard cover.
First person to agree to send me $5 gets them.
Anthony Clifton
PO Box 35533
Des Moines, Iowa 50315
28 Sep
28 Sep
5:26 a.m.
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9:51 a.m.
At 18:26 28/09/2001, Tony Duell wrote:
OK. There's no extraneous heat that I can detect, so presumably - unless
its in saturation - it's OK.
What I'll do next week is trace all the power wiring, so I've got some idea
of what pin (on the PSU connector) is doing what, which will give my
multimeter something to look at. And, I get an Oscilloscope on the 13th
October (huzzah!), so I'll point that at it as well; make sure the waveform
looks right.
Meantime, I've got a 3.5hr drive to do now, and it's late...
--
Cheers, Ade.
Be where it's at, B-Racing!
http://b-racing.co.uk
But I've
never seen a PET fitted with one of those.
OK, I'll go with you on that one. I'm basing my dual-tap idea on the fact
there's three lugs on the input side; I'd guessed that one might deliver
1/2 the voltage. I've not tested it in any meaningful way.
There are several possibilites.
Firstly, we have 50Hz mains, the US has 60Hz mains. Therefore, for a
given load current, smoothing capacitor value, and so on, there is more
ripple on a PSU in the UK than in the States. I doubt it's that marginal
('rock steady' -> 'wobbling' sounds a lot more than
'marginal'), but it
can't hurt to check.
I'm guessing there must be a rectifier up in the monitor, since that only
takes 20vac. Last time I looked, there's no really big caps up there
(unlike the one in the main case); maybe the VDU supply is more plausibly
marginal than the mainboard?
To give you some idea of the wobble - it's oscillating through around 1mm,
possibly a shade less. It's quite a rapid wobble - not 50 times a second
though. It seems pretty consistent across the whole screen, but possibly
slightly worse on the side of the main transformer. There's also a
noticable downward bend on the top line which doesn't seem to be present on
the bottom line. However, I went crosseyed trying to look at it.... I'll
have to set my camera up to shoot a short movie of it, so I can do a
frame-by-frame analysis of the motion (assuming that's necessary).
Secondly, stray magnetic fields from the transformer
could be affecting
the dispaly (by deflecting the electron beam -- electrons are not smart
enough to realise they should only be deflected by the fields from the
yoke :-)). Did you mount the new transformer in the same position _and
orientation_ as the original one.
Yes - I've not unmounted the transformer from its base plate, so I've no
choice about orientation. However, it may be orientated incorrectly on the
base plate of course.... Also, it's worth noting that the US transformer is
a different layout anyway (primary inside secondary, I think).
Thirdly, the machine might be designed to accommodate
stray fields and/or
ripple _at a particular frequency_. Typically the vertical deflection
frequency of the display will be the same as the mains frequency, so
although the ripple/stray fields will make the image slightly
non-straight, it won't wobble.
It's definitely wobbling, although as noted above there's some distortion
as well (actually, there's slight pincushion on all four sides).
Now, the 8032 uses a 6845 CRT controller chip IIRC. It
sets the sync
frequencies. Maybe it's configured differently on UK and US machines.
Maybe, therefore, one of the ROMs is different between UK and US machines
(I don't recall any setup links on the CPU board to configure this, as
some other manufacturers used). Does anybody know if UK PETs have 50Hz
vertical display systems? If they do, then you might need a dump of the
appropriate ROMs.
Hmm. The wobble is no different on the UK & US machines; so I'd be tempted
to not believe this is the case. The voltage plates are on the chassis of
the machine, as opposed to the transformer carrier (which is where they'd
make more sense IMHO), so I know the UK machine really *is* a UK machine.
I genuinely
don't know. That's the only part I've swapped in the new 8032.
Could a flakey transformer be making the screen wobble? How do
transformers
go flakey anyway, if indeed they *can* co flakey?
Or is the US chap
telling
Very unlikely. Transformers fail by open-circuit windings (no output) or
shorts between turns (wrong output and the thing gets _very_ hot), or
shorts from the windings to the core (ditto, sometimes blown fuses).
Overloading a transformer might saturate the core and increase the stray
field, but I think this is a very unlikely problem.
10:22 a.m.
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6 Oct
6 Oct
7:06 a.m.
New subject: CBM8032 - wobbly screen (The saga continues)
Curiouser and curiouser...
Today, I happened to have the machine opened up to effect some keyboard
repairs (i.e. a jolly good clean up). Having successfuly removed all traces
of key bounce, non-working keys, etc., and feeling justifiably please with
myself, it occurred to me to try a couple of things WRT the wobbly screen.
1st attempt: "build" some shielding out of aluminium foil to go around the
transformer. Which I did - all rough & ready stuff, with just a bit of
insulating tape over the transformer connections to make sure they didn't
short out. No effect - the screen wobbled its way along as ususal.
2nd attempt: Same as above, but this time I made absolutely sure the tin
foil was earthed, by screwing it onto the chassis via one of the
transformer screws. Same effect as 1st attempt: FA.
3rd attempt: Getting desparate now, I wrapped a load of tin foil around the
signal cables (having removed it from the transformer). Decided to leave
the lid up when I switched on and bingo! Steady as a rock (literally no
movement whatsoever. Refusing to get too excited, I carefully brought the
lid down (holding the signal cables so as not to let the tin foil touch the
circuit board - bah! The wobble returned.
4th attempt: Removed all tinfoil, started up with the lid open, no wobble.
The wobble appears progressively as the monitor approaches the transformer
(the lid down position).
5th attempt: Put a sheet of tinfoil over the whole of the bottom of the
monitor section. No effect - wobble remained.
Clearly, therefore, the wobble is induced by the monitor. There must be a
fairly monster field coming off the transformer interfering with the
electron gun aiming circuit(s), or something like that.
The question is: What *would* shield it? Do I need some thin steel or
copper, for example? Presumably, the shielding needs to be earthed (not
difficult, there's plenty of earth points around there. Or, would it be
easier to simply replace the big transformer with a smaller modern one?
TIA!
--
Cheers, Ade.
Be where it's at, B-Racing!
http://b-racing.co.uk
8:36 a.m.
New subject: CBM8032 - wobbly screen (The saga continues)
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1:07 p.m.
New subject: CBM8032 - wobbly screen (The saga continues)
At 21:36 06/10/2001, you wrote:
Okay, that makes sense. I *should* be able to get hold of some of this
"mu-metal" stuff - I know people at an electicity/electronics R&D lab....
:)
Ahem. Yes... Typing to quickly for my brain again, I'm afraid.
1st attempt:
"build" some shielding out of aluminium foil to go around the
transformer. Which I did - all rough & ready stuff, with just a bit of
Aluminium won't do a darn thing about 50Hz magnetic fields. You want
something like mild steel, or better still mu-metal (if you can get it at
a sensible price, or indeed, at all). Clearly,
therefore, the wobble is induced by the monitor. There must be a
^^^^^^^
transformer, surely... Now, if half of that goes open-circut (dead diode, bad
connection, etc)
the machine will most likely still work, but the stray field from the
transformer will increase. It's worth checking this...
I will have a poke around with my multimeter tomorrow...
--
Cheers, Ade.
Be where it's at, B-Racing!
http://b-racing.co.uk
7 Oct
7 Oct
6:31 a.m.
New subject: CBM8032 - wobbly screen (The saga continues)
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1:19 p.m.
New subject: CBM8032 - wobbly screen (The saga continues)
At 19:31 07/10/2001, you wrote:
lab.... :)
It's worth asking. Really you need to anneal it after bending it to
shape (bending it will affect the magnetic properties and will make it
less good as a sheild). But in practice if you don't bend it except at
the corners where you have to, it will be a lot better than nothing.
Anneal - is that where you heat it up & hit it with a hammer? Or do you
just heat it up and let it cool again? I forget now... It's been a long
long time since I had any metalwork lessons.
Well, a screwdriver bit. It's one of those 1.5in long bits which go into a
handle, or drill.
Aluminium won't do a darn thing about 50Hz magnetic
fields. You want
something like mild steel, or better still mu-metal (if you can get it at
a sensible price, or indeed, at all).
Okay, that makes sense. I *should* be able to get hold of some of this
"mu-metal" stuff - I know people at an electicity/electronics R&D
I will have a poke around with my multimeter tomorrow...
In another post you mentioned you could easily detect the stray field
with a screwdriver (ouch!). OK, take the loads off the transformer. Pull the power
connector off the
mainboard, and unplug the cable to the monitor. Is there still the same
stray field (if so, suspect shorted turns or similar in the transformer).
Yes, it's still there, albeit not quite so strongly. Still enough to induce
a noticable vibration in my magnet-on-a-stick.
If not, then reconnect one of the loads (say the
mainboard) and see what
the field is like now. Then try connecting the other load (monitor) on
its own and see what the field is like.
If one of the loads causes a rediculous increase in the field, then check
the rectifiers and smoothing capacitors in that section...
No, not ridiculous (at least, I don't think so), but there is a noticable
increase when the monitor load is added.
From this, can I deduce that:
a) The transformer is kaput (or, at least, on its way out)
b) There may be a borderline problem inside the monitor cabinet.
I've not got around to the multimeter test yet - I need to take the
mainboard out to access the underside, and that's not a task to be doing at
2:20am....
--
Cheers, Ade.
Be where it's at, B-Racing!
http://b-racing.co.uk
8 Oct
8 Oct
5:36 a.m.
New subject: CBM8032 - wobbly screen (The saga continues)
Anneal - is that where you heat it up & hit it
with a hammer? Or do you
just heat it up and let it cool again? I forget now... It's been a long
long time since I had any metalwork lessons.
Heat to cherry red, then cool very slowly, often covered in lime, IIRC,
to hold the heat in. The very slow cooling keeps the metal soft, vs
cooling quickly ( quenching ) to harden.
Adrian Vickers wrote:
> At 19:31 07/10/2001, you wrote:
>
> > > >Aluminium won't do a darn thing about 50Hz magnetic fields. You
want
> > > >something like mild steel, or better still mu-metal (if you can get it
at
> > > >a sensible price, or indeed, at all).
> > >
> > > Okay, that makes sense. I *should* be able to get hold of some of this
> > > "mu-metal" stuff - I know people at an electicity/electronics
R&D
> > lab.... :)
> >
> >It's worth asking. Really you need to anneal it after bending it to
> >shape (bending it will affect the magnetic properties and will make it
> >less good as a sheild). But in practice if you don't bend it except at
> >the corners where you have to, it will be a lot better than nothing.
>
Anneal - is that where you heat it up & hit it
with a hammer? Or do you
just heat it up and let it cool again? I forget now... It's been a long
long time since I had any metalwork lessons.
>
> > >
> > > I will have a poke around with my multimeter tomorrow...
> >
> >In another post you mentioned you could easily detect the stray field
> >with a screwdriver (ouch!).
>
> Well, a screwdriver bit. It's one of those 1.5in long bits which go into a
> handle, or drill.
>
> >OK, take the loads off the transformer. Pull the power connector off the
> >mainboard, and unplug the cable to the monitor. Is there still the same
> >stray field (if so, suspect shorted turns or similar in the transformer).
>
> Yes, it's still there, albeit not quite so strongly. Still enough to induce
> a noticable vibration in my magnet-on-a-stick.
>
> >If not, then reconnect one of the loads (say the mainboard) and see what
> >the field is like now. Then try connecting the other load (monitor) on
> >its own and see what the field is like.
> >
> >If one of the loads causes a rediculous increase in the field, then check
> >the rectifiers and smoothing capacitors in that section...
>
> No, not ridiculous (at least, I don't think so), but there is a noticable
> increase when the monitor load is added.
>
> From this, can I deduce that:
>
> a) The transformer is kaput (or, at least, on its way out)
> b) There may be a borderline problem inside the monitor cabinet.
>
> I've not got around to the multimeter test yet - I need to take the
> mainboard out to access the underside, and that's not a task to be doing at
> 2:20am....
>
> --
> Cheers, Ade.
> Be where it's at, B-Racing!
> http://b-racing.co.uk
>
> ------------------------------------------------------------------------
>
> ---
> Outgoing mail is certified Virus Free.
> Checked by AVG anti-virus system (http://www.grisoft.com).
> Version: 6.0.282 / Virus Database: 150 - Release Date: 25/09/2001
10:11 a.m.
New subject: CBM8032 - wobbly screen (The saga continues)
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9:27 p.m.
New subject: CBM8032 - wobbly screen (The saga continues)
At 23:11 08/10/2001, you wrote:
True....
induce
I've got 4 PETs of various types here: The 2001 & 3016 have transformers
with steel bands around them - the 2001 screen is stable, the 3016 wobbles,
but almost imperceptably.
The 8032 and 8032-SK have a different type of transformer (without the
steel band), and wobble very noticably. It could have been a cost-cutting
exercise by CBM, with the result that the 8032 transformers are breaking
down more quickly.
I shall give it a try tonight.
Hmm, I get tired & clumsy after about 1am - I start losing bits, forgetting
to make sure I'm earthed before touching chips & things. Far safer to
switch the 'phone off and do it straight after work...
--
Cheers, Ade.
Be where it's at, B-Racing!
http://b-racing.co.uk
Well, a screwdriver bit. It's one of those
1.5in long bits which go into a
handle, or drill.
OK. Still a fair size piece of metal to move, and thus a fair size
external field. OK, take the loads off the transformer. Pull the power
connector off the
mainboard, and unplug the cable to the monitor. Is there still the same
stray field (if so, suspect shorted turns or similar in the transformer).
Yes, it's still there, albeit not quite so strongly. Still enough to a noticable vibration in my magnet-on-a-stick.
It does sound as though you have transformer problems. You're making me
curious enough to dig out one of my PETs and experiment with the
transformer sometime just to see what I can detect. No, not
ridiculous (at least, I don't think so), but there is a noticable
increase when the monitor load is added.
Interesting. So it might be PSU problems in the monitor. IIRC the monitor
has a bridge rectifier input circuit. Check all 4 diodes and the
soldering to them. If one is open you might have problems like this. I've not
got around to the multimeter test yet - I need to take the
mainboard out to access the underside, and that's not a task to be
doing at
2:20am....
Odd, I normally do delicate work like that at night. It's the one time
you are not going to be disturbed while working on the system... 
6 Oct
6 Oct
8:45 a.m.
New subject: CBM8032 - wobbly screen (The saga continues)
I doubt a new transformer will help this very much. If this box ever worked
right, then something's changed, and the filter CAPs are a prime suspect after
all these years. I'd look for a failed diode in a 4-diode bridge too, if that's
what they used. However, what's more likely is a problem in the wiring, since
the wiring path changes as you open/close the lid. Since increased shielding
didn't do much, perhaps you should look at the power connections, as the cabling
is perturbed whenever the box is opened. If you check underneath (on the solder
side) the supply connections on the main board and, more likely, on the CRT
board, perhaps you'll see a deteriorated connection or possible damaged trace
that moves around when you wiggle the power wiring. It could even be a badly
seated/latched contact in a MOLEX shell if that's what they used. I don't think
Commodore made the CRT board, and they may have used a pretty shoddy monitor.
You've apparently got to find something that's different between when the box is
open versus when it's closed.
Dick
----- Original Message -----
From: "Adrian Vickers" <avickers(a)solutionengineers.com>
To: <classiccmp(a)classiccmp.org>
Sent: Saturday, October 06, 2001 1:06 PM
Subject: Re: CBM8032 - wobbly screen (The saga continues)
Curiouser and curiouser...
Today, I happened to have the machine opened up to effect some keyboard
repairs (i.e. a jolly good clean up). Having successfuly removed all traces
of key bounce, non-working keys, etc., and feeling justifiably please with
myself, it occurred to me to try a couple of things WRT the wobbly screen.
1st attempt: "build" some shielding out of aluminium foil to go around the
transformer. Which I did - all rough & ready stuff, with just a bit of
insulating tape over the transformer connections to make sure they didn't
short out. No effect - the screen wobbled its way along as ususal.
2nd attempt: Same as above, but this time I made absolutely sure the tin
foil was earthed, by screwing it onto the chassis via one of the
transformer screws. Same effect as 1st attempt: FA.
3rd attempt: Getting desparate now, I wrapped a load of tin foil around the
signal cables (having removed it from the transformer). Decided to leave
the lid up when I switched on and bingo! Steady as a rock (literally no
movement whatsoever. Refusing to get too excited, I carefully brought the
lid down (holding the signal cables so as not to let the tin foil touch the
circuit board - bah! The wobble returned.
4th attempt: Removed all tinfoil, started up with the lid open, no wobble.
The wobble appears progressively as the monitor approaches the transformer
(the lid down position).
5th attempt: Put a sheet of tinfoil over the whole of the bottom of the
monitor section. No effect - wobble remained.
Clearly, therefore, the wobble is induced by the monitor. There must be a
fairly monster field coming off the transformer interfering with the
electron gun aiming circuit(s), or something like that.
The question is: What *would* shield it? Do I need some thin steel or
copper, for example? Presumably, the shielding needs to be earthed (not
difficult, there's plenty of earth points around there. Or, would it be
easier to simply replace the big transformer with a smaller modern one?
TIA!
--
Cheers, Ade.
Be where it's at, B-Racing!
http://b-racing.co.uk
--------------------------------------------------------------------------------
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Outgoing mail is certified Virus Free.
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10:15 a.m.
New subject: CBM8032 - wobbly screen (The saga continues)
I have to disagree.
What Adrian describes are the "classical" symptoms for electromagnetic
inductions,
resp. distortions caused by this physical effect. Grounding and
shielding with tin
foil does not help, since it's the transformers magnetic field (as
opposed to an
electrostatic field, that would be shielded by the grounded foil) that
deflects the
electrons of the CRT beam and causes the wobble.
Tha most probable cause is indeed the transformer, more precisely: the
aging core
of the transformer. This core usually is made of a lot of thin sheets of
steel.
The purpose of the core is to a) couple the primary and secondary coils
very
closely and, more important b) to "contain" and keep the electromagnetic
field
closely within the transformer. Well, ok, that's a bit simplistic, but
you'll get
the idea. The core is not made out of a compact piece of steel since
stray currents
would be induced within the steel, heating up the core and wasting
energy. This stray
currents ("eddies" they're called in english, i think...) would be
induced perpendicular
to the orientation of the sheets the transformer core is made of.
Thus, these sheets must be insulated by very thin layers of plastic or
resin or something
similar.
Now, this is the point: With old transformers, this insulation starts to
literally crumble
away, which leads to a significantly larger stray magnetic field around
the transformer.
Later, you can usually **HEAR** this effect: the steel sheets start to
humm with the
line frequency. The transformer is close to dead now...
To make this log story short: Yes, a new transformer should help. New,
like in
"factory fresh"...
Even better would be one of these fancy and expensive torroid
trasformers, since
they have literally no measurable magnetic field outside the core.
Shielding of the old transformer is no real option. You would need what
we Germans
call "mu-Metal", which is a special alloy of steel and other things i
have long
forgotten but that make it EXPENSIVE.
It is magnetic, but not a good conductor, which make it ideal for
shielding magnetic
fields.
You could try a shielding out of steel sheets, but they might get hot if
the stray
currents induced by the transformers magnetic field are too large. And
the shielding
effect is not too good...
Oh, and by the way: I'm new to this list... 8-)
Hi, i'm Michael and i am collecting old VAXen.
I live somewhere in southern Germany, which is not that bad. No,
really.... 8-)
Cheers
ms
P.S.: sorry for the long post...
Richard Erlacher wrote:
I doubt a new transformer will help this very much. If this box ever worked
right, then something's changed, and the filter CAPs are a prime suspect after
all these years. I'd look for a failed diode in a 4-diode bridge too, if that's
what they used. However, what's more likely is a problem in the wiring, since
the wiring path changes as you open/close the lid. Since increased shielding
didn't do much, perhaps you should look at the power connections, as the cabling
is perturbed whenever the box is opened. If you check underneath (on the solder
side) the supply connections on the main board and, more likely, on the CRT
board, perhaps you'll see a deteriorated connection or possible damaged trace
that moves around when you wiggle the power wiring. It could even be a badly
seated/latched contact in a MOLEX shell if that's what they used. I don't think
Commodore made the CRT board, and they may have used a pretty shoddy monitor.
You've apparently got to find something that's different between when the box is
open versus when it's closed.
Dick
----- Original Message -----
From: "Adrian Vickers" <avickers(a)solutionengineers.com>
To: <classiccmp(a)classiccmp.org>
Sent: Saturday, October 06, 2001 1:06 PM
Subject: Re: CBM8032 - wobbly screen (The saga continues)
--
Michael Schneider email (home): ms(a)silke.rt.schwaben.de
Schleestr.8 http://www.vaxcluster.de
72766 Reutlingen Phone: +49 7121 492781
Germany FAX: +49 7121 479331
People disagree with me. I just ignore them.
(Linus Torvalds)
Curiouser and curiouser...
Today, I happened to have the machine opened up to effect some keyboard
repairs (i.e. a jolly good clean up). Having successfuly removed all traces
of key bounce, non-working keys, etc., and feeling justifiably please with
myself, it occurred to me to try a couple of things WRT the wobbly screen.
1st attempt: "build" some shielding out of aluminium foil to go around the
transformer. Which I did - all rough & ready stuff, with just a bit of
insulating tape over the transformer connections to make sure they didn't
short out. No effect - the screen wobbled its way along as ususal.
2nd attempt: Same as above, but this time I made absolutely sure the tin
foil was earthed, by screwing it onto the chassis via one of the
transformer screws. Same effect as 1st attempt: FA.
3rd attempt: Getting desparate now, I wrapped a load of tin foil around the
signal cables (having removed it from the transformer). Decided to leave
the lid up when I switched on and bingo! Steady as a rock (literally no
movement whatsoever. Refusing to get too excited, I carefully brought the
lid down (holding the signal cables so as not to let the tin foil touch the
circuit board - bah! The wobble returned.
4th attempt: Removed all tinfoil, started up with the lid open, no wobble.
The wobble appears progressively as the monitor approaches the transformer
(the lid down position).
5th attempt: Put a sheet of tinfoil over the whole of the bottom of the
monitor section. No effect - wobble remained.
Clearly, therefore, the wobble is induced by the monitor. There must be a
fairly monster field coming off the transformer interfering with the
electron gun aiming circuit(s), or something like that.
The question is: What *would* shield it? Do I need some thin steel or
copper, for example? Presumably, the shielding needs to be earthed (not
difficult, there's plenty of earth points around there. Or, would it be
easier to simply replace the big transformer with a smaller modern one?
TIA!
--
Cheers, Ade.
Be where it's at, B-Racing!
http://b-racing.co.uk
--------------------------------------------------------------------------------
>
> ---
> Outgoing mail is certified Virus Free.
> Checked by AVG anti-virus system (http://www.grisoft.com).
> Version: 6.0.282 / Virus Database: 150 - Release Date: 25/09/2001
>
11:15 a.m.
New subject: CBM8032 - wobbly screen (The saga continues)
What Michael says here makes a great deal of sense. However, as I have a number
of units which, like the Commodore box, have a transformer of considerable age
in their power supply located near the yoke of the CRT, yet have none of the
wobble described here, it seems to me that one could probably allow the
transformer in the Commodore unit to remain at least long enough to check for
some sort of disruption of the power supply to the sweep circuits. Transformers
should last longer than this 20 years or so, while the capacitors have reached
their shelf-life limits, I think.
Partly, I guess, this bias is because I'm quite certain it will be a lot of
trouble replacing the original transformer, though a kit with appropriate spec's
might be solution. In any case, one can check the power supply connections to
the CRT circuitry without leaving the house. This being Saturday, I'd say
Monday will be soon enough to go searching for a replacement transformer.
Let's keep our fingers crossed ...
Dick
----- Original Message -----
From: "Michael Schneider" <ms(a)silke.rt.schwaben.de>
To: <classiccmp(a)classiccmp.org>
Sent: Saturday, October 06, 2001 4:15 PM
Subject: Re: CBM8032 - wobbly screen (The saga continues)
------------------------------------------------------------------------------ --
I have to disagree.
What Adrian describes are the "classical" symptoms for electromagnetic
inductions,
resp. distortions caused by this physical effect. Grounding and
shielding with tin
foil does not help, since it's the transformers magnetic field (as
opposed to an
electrostatic field, that would be shielded by the grounded foil) that
deflects the
electrons of the CRT beam and causes the wobble.
Tha most probable cause is indeed the transformer, more precisely: the
aging core
of the transformer. This core usually is made of a lot of thin sheets of
steel.
The purpose of the core is to a) couple the primary and secondary coils
very
closely and, more important b) to "contain" and keep the electromagnetic
field
closely within the transformer. Well, ok, that's a bit simplistic, but
you'll get
the idea. The core is not made out of a compact piece of steel since
stray currents
would be induced within the steel, heating up the core and wasting
energy. This stray
currents ("eddies" they're called in english, i think...) would be
induced perpendicular
to the orientation of the sheets the transformer core is made of.
Thus, these sheets must be insulated by very thin layers of plastic or
resin or something
similar.
Now, this is the point: With old transformers, this insulation starts to
literally crumble
away, which leads to a significantly larger stray magnetic field around
the transformer.
Later, you can usually **HEAR** this effect: the steel sheets start to
humm with the
line frequency. The transformer is close to dead now...
To make this log story short: Yes, a new transformer should help. New,
like in
"factory fresh"...
Even better would be one of these fancy and expensive torroid
trasformers, since
they have literally no measurable magnetic field outside the core.
Shielding of the old transformer is no real option. You would need what
we Germans
call "mu-Metal", which is a special alloy of steel and other things i
have long
forgotten but that make it EXPENSIVE.
It is magnetic, but not a good conductor, which make it ideal for
shielding magnetic
fields.
You could try a shielding out of steel sheets, but they might get hot if
the stray
currents induced by the transformers magnetic field are too large. And
the shielding
effect is not too good...
Oh, and by the way: I'm new to this list... 8-)
Hi, i'm Michael and i am collecting old VAXen.
I live somewhere in southern Germany, which is not that bad. No,
really.... 8-)
Cheers
ms
P.S.: sorry for the long post...
Richard Erlacher wrote:
>
> I doubt a new transformer will help this very much. If this box ever worked
> right, then something's changed, and the filter CAPs are a prime suspect
after
> all these years. I'd look for a failed diode
in a 4-diode bridge too, if
that's
> what they used. However, what's more likely
is a problem in the wiring,
since
> the wiring path changes as you open/close the
lid. Since increased
shielding
> didn't do much, perhaps you should look at
the power connections, as the
cabling
> is perturbed whenever the box is opened. If you
check underneath (on the
solder
> side) the supply connections on the main board
and, more likely, on the CRT
> board, perhaps you'll see a deteriorated connection or possible damaged
trace
> that moves around when you wiggle the power
wiring. It could even be a
badly
> seated/latched contact in a MOLEX shell if
that's what they used. I don't
think
> Commodore made the CRT board, and they may have
used a pretty shoddy
monitor.
>
> You've apparently got to find something that's different between when the
box is
> open versus when it's closed.
>
> Dick
>
> ----- Original Message -----
> From: "Adrian Vickers" <avickers(a)solutionengineers.com>
> To: <classiccmp(a)classiccmp.org>
> Sent: Saturday, October 06, 2001 1:06 PM
> Subject: Re: CBM8032 - wobbly screen (The saga continues)
>
> > Curiouser and curiouser...
> >
> > Today, I happened to have the machine opened up to effect some keyboard
> > repairs (i.e. a jolly good clean up). Having successfuly removed all
traces
> > of key bounce, non-working keys, etc., and
feeling justifiably please with
> > myself, it occurred to me to try a couple of things WRT the wobbly screen.
> >
> > 1st attempt: "build" some shielding out of aluminium foil to go
around the
> > transformer. Which I did - all rough & ready stuff, with just a bit of
> > insulating tape over the transformer connections to make sure they didn't
> > short out. No effect - the screen wobbled its way along as ususal.
> >
> > 2nd attempt: Same as above, but this time I made absolutely sure the tin
> > foil was earthed, by screwing it onto the chassis via one of the
> > transformer screws. Same effect as 1st attempt: FA.
> >
> > 3rd attempt: Getting desparate now, I wrapped a load of tin foil around
the
> > signal cables (having removed it from the
transformer). Decided to leave
> > the lid up when I switched on and bingo! Steady as a rock (literally no
> > movement whatsoever. Refusing to get too excited, I carefully brought the
> > lid down (holding the signal cables so as not to let the tin foil touch
the
circuit board - bah! The wobble returned.
4th attempt: Removed all tinfoil, started up with the lid open, no wobble.
The wobble appears progressively as the monitor approaches the transformer
(the lid down position).
5th attempt: Put a sheet of tinfoil over the whole of the bottom of the
monitor section. No effect - wobble remained.
Clearly, therefore, the wobble is induced by the monitor. There must be a
fairly monster field coming off the transformer interfering with the
electron gun aiming circuit(s), or something like that.
The question is: What *would* shield it? Do I need some thin steel or
copper, for example? Presumably, the shielding needs to be earthed (not
difficult, there's plenty of earth points around there. Or, would it be
easier to simply replace the big transformer with a smaller modern one?
TIA!
--
Cheers, Ade.
Be where it's at, B-Racing!
http://b-racing.co.uk
>
> ---
> Outgoing mail is certified Virus Free.
> Checked by AVG anti-virus system (http://www.grisoft.com).
> Version: 6.0.282 / Virus Database: 150 - Release Date: 25/09/2001
>
--
Michael Schneider email (home): ms(a)silke.rt.schwaben.de
Schleestr.8 http://www.vaxcluster.de
72766 Reutlingen Phone: +49 7121 492781
Germany FAX: +49 7121 479331
People disagree with me. I just ignore them.
(Linus Torvalds)
1:20 p.m.
New subject: CBM8032 - wobbly screen (The saga continues)
At 00:15 07/10/2001, Dick wrote:
What Michael says here makes a great deal of sense.
However, as I have a
number
of units which, like the Commodore box, have a transformer of considerable age
in their power supply located near the yoke of the CRT, yet have none of the
wobble described here, it seems to me that one could probably allow the
transformer in the Commodore unit to remain at least long enough to check for
some sort of disruption of the power supply to the sweep
circuits. Transformers
should last longer than this 20 years or so, while the capacitors have reached
their shelf-life limits, I think.
Yes, I'm still concerned about the capacitors. However, caps shouldn't
induce the wobble in one orientation, but not another.... So the
transformer is my current prime suspect.
Partly, I guess, this bias is because I'm quite
certain it will be a lot of
trouble replacing the original transformer, though a kit with appropriate
spec's
might be solution. In any case, one can check the power supply connections to
the CRT circuitry without leaving the house. This being Saturday, I'd say
Monday will be soon enough to go searching for a replacement transformer.
Monday will be soon enough for everything.... I'm with the Irish on this
one (when told of a Spanish word - Manyana (sp?) - meaning "as God wills
it", the Irishman pondered for a while then retorted "We have no word or
phrase which conveys such a sense of *urgency*...)
Anyway, I shall probably try sticking a sheet of iron or steel in there;
hopefully that will show an improvement. If so, I can try to get hold of
some of this mu-metal stuff, and give that a whirl. Then there's... (well,
see some of my other posts for the rapidly growing to-do list :)
Let's keep our fingers crossed ...
Indeed so!
Thanks again!
--
Cheers, Ade.
Be where it's at, B-Racing!
http://b-racing.co.uk
7 Oct
7 Oct
8:01 a.m.
New subject: CBM8032 - wobbly screen (The saga continues)
All this talk about magnetically induced wobble makes me remember
the time that I lived in a third floor apartment; the 13.2KV
distribution lines feeding a nearby refrigerator/stove factory were
about 10ft away from my window (and my monitor). I could tell
very easily when the porcellanization electric furnace at
the factory was turned on or off. I was able to measure
fields in excess of 300 milligauss at the window, though
they practically dissapeared by the bedroom.
Those 13.2KV lines were good earthquake detectors as well.
I remember seeing them dancing around before I could feel
the actual vibration, which eventually grew into a
deadly 7.2 quake that killed a couple hundred in a nearby
city.
I prefer single-level houses now.
--------------------------------------------------------------
Carlos E. Murillo-Sanchez carlos_murillo(a)nospammers.ieee.org
8 Oct
8 Oct
9:48 a.m.
New subject: CBM8032 - wobbly screen (The saga continues)
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6 Oct
6 Oct
9:43 p.m.
New subject: CBM8032 - wobbly screen (The saga continues)
Well, it's not that the transformer HAS to die....
Adrian should try to listen to the thing: If he clearly hears the
transformer
humming under load, throw it away. Or: place small magnetic objects very
close
to the transformers core. You need a considerably large magnetic field
on the
surface of the core to influence the electrons in the CRT's beam, which
are,
after all, still a few inches away. So, the "small objects" might
move...
Oh, another idea: Adrian, have you tried to place the transformer on the
table,
outside of the casing? I mean: leave as much as possible of the original
cabling
in place, just put the transformer out of the way? If this helps, you
know
what to do 8-)
Richard Erlacher wrote:
What Michael says here makes a great deal of sense. However, as I have a number
of units which, like the Commodore box, have a transformer of considerable age
in their power supply located near the yoke of the CRT, yet have none of the
wobble described here, it seems to me that one could probably allow the
transformer in the Commodore unit to remain at least long enough to check for
some sort of disruption of the power supply to the sweep circuits. Transformers
should last longer than this 20 years or so, while the capacitors have reached
their shelf-life limits, I think.
Partly, I guess, this bias is because I'm quite certain it will be a lot of
trouble replacing the original transformer, though a kit with appropriate spec's
might be solution. In any case, one can check the power supply connections to
the CRT circuitry without leaving the house. This being Saturday, I'd say
Monday will be soon enough to go searching for a replacement transformer.
Let's keep our fingers crossed ...
Dick
----- Original Message -----
From: "Michael Schneider" <ms(a)silke.rt.schwaben.de>
To: <classiccmp(a)classiccmp.org>
Sent: Saturday, October 06, 2001 4:15 PM
Subject: Re: CBM8032 - wobbly screen (The saga continues)
------------------------------------------------------------------------------ --
> >
> > >
> > > ---
> > > Outgoing mail is certified Virus Free.
> > > Checked by AVG anti-virus system (http://www.grisoft.com).
> > > Version: 6.0.282 / Virus Database: 150 - Release Date: 25/09/2001
> > >
>
> --
> Michael Schneider email (home): ms(a)silke.rt.schwaben.de
> Schleestr.8 http://www.vaxcluster.de
> 72766 Reutlingen Phone: +49 7121 492781
> Germany FAX: +49 7121 479331
>
> People disagree with me. I just ignore them.
> (Linus Torvalds)
>
>
--
Michael Schneider email (home): ms(a)silke.rt.schwaben.de
Schleestr.8 http://www.vaxcluster.de
72766 Reutlingen Phone: +49 7121 492781
Germany FAX: +49 7121 479331
People disagree with me. I just ignore them.
(Linus Torvalds)
I have to disagree.
What Adrian describes are the "classical" symptoms for electromagnetic
inductions,
resp. distortions caused by this physical effect. Grounding and
shielding with tin
foil does not help, since it's the transformers magnetic field (as
opposed to an
electrostatic field, that would be shielded by the grounded foil) that
deflects the
electrons of the CRT beam and causes the wobble.
Tha most probable cause is indeed the transformer, more precisely: the
aging core
of the transformer. This core usually is made of a lot of thin sheets of
steel.
The purpose of the core is to a) couple the primary and secondary coils
very
closely and, more important b) to "contain" and keep the electromagnetic
field
closely within the transformer. Well, ok, that's a bit simplistic, but
you'll get
the idea. The core is not made out of a compact piece of steel since
stray currents
would be induced within the steel, heating up the core and wasting
energy. This stray
currents ("eddies" they're called in english, i think...) would be
induced perpendicular
to the orientation of the sheets the transformer core is made of.
Thus, these sheets must be insulated by very thin layers of plastic or
resin or something
similar.
Now, this is the point: With old transformers, this insulation starts to
literally crumble
away, which leads to a significantly larger stray magnetic field around
the transformer.
Later, you can usually **HEAR** this effect: the steel sheets start to
humm with the
line frequency. The transformer is close to dead now...
To make this log story short: Yes, a new transformer should help. New,
like in
"factory fresh"...
Even better would be one of these fancy and expensive torroid
trasformers, since
they have literally no measurable magnetic field outside the core.
Shielding of the old transformer is no real option. You would need what
we Germans
call "mu-Metal", which is a special alloy of steel and other things i
have long
forgotten but that make it EXPENSIVE.
It is magnetic, but not a good conductor, which make it ideal for
shielding magnetic
fields.
You could try a shielding out of steel sheets, but they might get hot if
the stray
currents induced by the transformers magnetic field are too large. And
the shielding
effect is not too good...
Oh, and by the way: I'm new to this list... 8-)
Hi, i'm Michael and i am collecting old VAXen.
I live somewhere in southern Germany, which is not that bad. No,
really.... 8-)
Cheers
ms
P.S.: sorry for the long post...
Richard Erlacher wrote:
>
> I doubt a new transformer will help this very much. If this box ever worked
> right, then something's changed, and the filter CAPs are a prime suspect
after
> all these years. I'd look for a failed
diode in a 4-diode bridge too, if
that's
> what they used. However, what's more
likely is a problem in the wiring,
since
> the wiring path changes as you open/close
the lid. Since increased
shielding
> didn't do much, perhaps you should look
at the power connections, as the
cabling
> is perturbed whenever the box is opened. If
you check underneath (on the
solder
> side) the supply connections on the main
board and, more likely, on the CRT
> board, perhaps you'll see a deteriorated connection or possible damaged
trace
> that moves around when you wiggle the power
wiring. It could even be a
badly
> seated/latched contact in a MOLEX shell if
that's what they used. I don't
think
> Commodore made the CRT board, and they may
have used a pretty shoddy
monitor.
>
> You've apparently got to find something that's different between when the
box is
> open versus when it's closed.
>
> Dick
>
> ----- Original Message -----
> From: "Adrian Vickers" <avickers(a)solutionengineers.com>
> To: <classiccmp(a)classiccmp.org>
> Sent: Saturday, October 06, 2001 1:06 PM
> Subject: Re: CBM8032 - wobbly screen (The saga continues)
>
> > Curiouser and curiouser...
> >
> > Today, I happened to have the machine opened up to effect some keyboard
> > repairs (i.e. a jolly good clean up). Having successfuly removed all
traces
> > of key bounce, non-working keys, etc.,
and feeling justifiably please with
> > myself, it occurred to me to try a couple of things WRT the wobbly screen.
> >
> > 1st attempt: "build" some shielding out of aluminium foil to go
around the
> > transformer. Which I did - all rough & ready stuff, with just a bit of
> > insulating tape over the transformer connections to make sure they didn't
> > short out. No effect - the screen wobbled its way along as ususal.
> >
> > 2nd attempt: Same as above, but this time I made absolutely sure the tin
> > foil was earthed, by screwing it onto the chassis via one of the
> > transformer screws. Same effect as 1st attempt: FA.
> >
> > 3rd attempt: Getting desparate now, I wrapped a load of tin foil around
the
> > signal cables (having removed it from
the transformer). Decided to leave
> > the lid up when I switched on and bingo! Steady as a rock (literally no
> > movement whatsoever. Refusing to get too excited, I carefully brought the
> > lid down (holding the signal cables so as not to let the tin foil touch
the
circuit board - bah! The wobble returned.
4th attempt: Removed all tinfoil, started up with the lid open, no wobble.
The wobble appears progressively as the monitor approaches the transformer
(the lid down position).
5th attempt: Put a sheet of tinfoil over the whole of the bottom of the
monitor section. No effect - wobble remained.
Clearly, therefore, the wobble is induced by the monitor. There must be a
fairly monster field coming off the transformer interfering with the
electron gun aiming circuit(s), or something like that.
The question is: What *would* shield it? Do I need some thin steel or
copper, for example? Presumably, the shielding needs to be earthed (not
difficult, there's plenty of earth points around there. Or, would it be
easier to simply replace the big transformer with a smaller modern one?
TIA!
--
Cheers, Ade.
Be where it's at, B-Racing!
http://b-racing.co.uk
11:30 p.m.
New subject: CBM8032 - wobbly screen (The saga continues)
At 10:43 07/10/2001, Michael Schneider wrote:
Well, it's not that the transformer HAS to die....
Adrian should try to listen to the thing: If he clearly hears the
transformer
humming under load, throw it away.
No, there is no significant noise from it. There's quite a powerful hum
just as it starts up, but that only lasts 1/2 a second or so before it goes
as good as silent.
Or: place small magnetic objects very
close
to the transformers core. You need a considerably large magnetic field
on the
surface of the core to influence the electrons in the CRT's beam, which
are,
after all, still a few inches away. So, the "small objects" might
move...
OK, I did two tests. Firstly with a telescopic magnet-on-a-stick thing
(used for picking up screws & the like from dark corners where they
inevitably fall) - the transformer induces a noticable vibration in that.
Secondly, I put a small screwdriver bit on top of the transformer. When
switching on, it tried to twist around (it actually did twist, but was
thwarted by the plastic ridges on the transformer).
Conclusion: This transformer IS putting out a very strong magnetic field...
Oh, another idea: Adrian, have you tried to place the
transformer on the
table,
outside of the casing? I mean: leave as much as possible of the original
cabling
in place, just put the transformer out of the way? If this helps, you
know
what to do 8-)
This is actually something I was thinking about last night. I could easily
fabricate a connector in the back of the computer, then move the
transformer out into its own box. OK, it wouldn't be "authentic PET" any
more, but it would completely cure the wobble. This may end up being the
only solution for my 8032-SK, since the transformer is so close to the
monitor that there's nowhere to put any shielding. I can't put the
transformer outside as it is, since the internal wiring is not long enough.
The other possible problem I'll have with shielding is: It's going to be
trying to move about in the magnetic field, isn't it? Meaning I'll have to
bolt it down pretty firmly to prevent it making too much noise...
Another possibility is to build a very simple step-down box (2-1) so I can
use the American transformer (which originally came with the machine); I
may pursue this option anyway since I now have two US-sourced CBM disk
drives, both of which require 115vac.
Yet another option - I could try re-orientating the transformer so the
magnetic pollution is pointing towards the front & rear of the machine,
instead of up & down like it is now. To do that, however, I'll need to
fabricate some kind of mounting bracket, and I don't have the material or
tools to do that right now. Also, I'm not sure how effective that'll be...
--
Cheers, Ade.
Be where it's at, B-Racing!
http://b-racing.co.uk
1:14 p.m.
New subject: CBM8032 - wobbly screen (The saga continues)
Hi Michael, welcome to the list! I hope it proves as useful to you as it
has to me (so far) - I only hope I can be as useful myself someday...
At 23:15 06/10/2001, you wrote:
Tha most probable cause is indeed the transformer, more
precisely: the
aging core
of the transformer. This core usually is made of a lot of thin sheets of
steel.
[snip excellent description - and yes, eddies is correct]
Now, this is the point: With old transformers, this
insulation starts to
literally crumble
away, which leads to a significantly larger stray magnetic field around
the transformer.
I can see how this could be the case. for instance, I can't believe that
Commodore would have let the units out of the door 20 years ago with as
much screen wobble as is present in mine. In fact - I know they didn't, as
about 10 years ago I used an 8032-SK for quite some time, and that
definitely didn't wobble.
Shielding of the old transformer is no real option. You
would need what
we Germans
call "mu-Metal", which is a special alloy of steel and other things i
have long
forgotten but that make it EXPENSIVE.
It is magnetic, but not a good conductor, which make it ideal for
shielding magnetic
fields.
Oh, I don't know. I can probably get hold of some for relatively little
money (beer tokens, if that).
You could try a shielding out of steel sheets, but they
might get hot if
the stray
currents induced by the transformers magnetic field are too large. And
the shielding
effect is not too good...
I may give something like that a whirl, just to check it is the problem.
I'll also be having a poke around to make sure it's not being unnecessarily
amplified by a component failure. And the caps are still on the list... :)
When I've finished this one, I've got two more to do.... AND there's
another 8032 to breath life back into (that one is more seriously broken).
I can see I'm not going to have much time left over to do my motor
racing.... :)
I live somewhere in southern Germany, which is not that
bad. No,
really.... 8-)
Well, it's got to be warmer and drier than the UK....
--
Cheers, Ade.
Be where it's at, B-Racing!
http://b-racing.co.uk
10 p.m.
New subject: CBM8032 - wobbly screen (The saga continues)
Adrian Vickers wrote:
Hmmm, the Romans did'nt want to settle here in Reutlingen, because
it has been a swamp area, whith lot's of rain!
But it is warm sometimes, that's true...
ms
Hi Michael, welcome to the list! I hope it proves as useful to you as it
has to me (so far) - I only hope I can be as useful myself someday...
Thank you for the warm welcome!
At 23:15 06/10/2001, you wrote:
>Tha most probable cause is indeed the transformer, more precisely: the
...
I can see how this could be the case. for instance, I can't believe that
Commodore would have let the units out of the door 20 years ago with as
much screen wobble as is present in mine. In fact - I know they didn't, as
about 10 years ago I used an 8032-SK for quite some time, and that
definitely didn't wobble.
That's true. But they let out units with rather cheap transformers. It
has
always been a significant cost factor to use a good, high quality
transformer
core. I mean, the best ones come from Germay, right ? 8-)
>Shielding of the old transformer is no real option. You would need what
>we Germans
...
>call "mu-Metal", which is a special
alloy of steel and other things i
...
I live somewhere in southern Germany, which is not
that bad. No,
really.... 8-)
Well, it's got to be warmer and drier than the UK....
--
Cheers, Ade.
Be where it's at, B-Racing!
http://b-racing.co.uk
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--
Michael Schneider email (home): ms(a)silke.rt.schwaben.de
Schleestr.8 http://www.vaxcluster.de
72766 Reutlingen Phone: +49 7121 492781
Germany FAX: +49 7121 479331
People disagree with me. I just ignore them.
(Linus Torvalds)
7 Oct
7 Oct
12:08 a.m.
New subject: CBM8032 - wobbly screen (The saga continues)
At 02:14 AM 07/10/2001 +0100, you wrote:
Cheers, Ade.
Be where it's at, B-Racing!
http://b-racing.co.uk
Just by chance, do you have space to rotate the transformer? Back
in 1950, when I was getting into TV repair, Ontario power grid was on 25
Hz! We had people bringing in 60 Hz TV sets from the US and asking us to
convert them to operate here. Also 25 Hz transformers were longer, which
raised them closer to the crt neck. Solutions included making an external
power supply, raising the chassis on stilts and putting the transformer
below, or sometimes if we were lucky, we could rotate the transformer
about 45 degrees and get away with it.
Good luck
Charlie Fox
Chas E. Fox Video Productions
793 Argyle Rd. Windsor ON N8Y 3J8
foxvideo(a)wincom.net
Check out:
Camcorder Kindergarten at http://chasfoxvideo.com
8435
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27 comments
11 participants
participants (11)
-
ard＠p850ug1.demon.co.uk -
avickers＠solutionengineers.com -
cmurillo＠emtelsa.multi.net.co -
donm＠cts.com -
edick＠idcomm.com -
foxvideo＠wincom.net -
jhellige＠earthlink.net -
ms＠silke.rt.schwaben.de -
vaxcat＠retrocomputing.com -
vze2mnvr＠verizon.net -
whdawson＠mlynk.com