8 Dec
2009
8 Dec
'09
4:23 a.m.
Picked up an old terminal in very nice cosmetic condition; it works fine
barring a bit of visual "jitter" on the display -- not sure how best to
describe it. The picture is clear and sharp but occasionally a few
scanlines will spike off to the right a bit. Coinciding with this
spiking are tiny crackling noises from inside the monitor. (Or at least
it seems like they coincide, obviously I can't verify this.)
I thought it might be HV leakage based on discussions I've seen on this
list. I've run it with the cover off and the lights off and I can see
no evidence of sparking or other visible discharge.
Any thoughts?
I hate working on CRTs. I'm not great with electronics (getting slowly
better) but I can handle debugging low voltage stuff. Fixing monitors
scares the heck out of me...
- Josh
8 Dec
8 Dec
4:37 a.m.
On 7 Dec 2009 at 19:23, Josh Dersch wrote:
I thought it might be HV leakage based on discussions
I've seen on
this list. I've run it with the cover off and the lights off and I
can see no evidence of sparking or other visible discharge.
Any thoughts?
My first instinct says "flyback transformer". An arc between
windings or the core/frame can produce the effect you describe
without anything visible showing.
--Chuck
4:46 a.m.
On Mon, Dec 7, 2009 at 9:23 PM, Josh Dersch <derschjo at mail.msu.edu> wrote:
Picked up an old terminal in very nice cosmetic
condition;
Funny you should post this. I was about to post about my Sony Multiscan
400PS monitor. It flashes on and off about once a second every second. I
don't know much about how to fix monitors. I know the theory, but wouldn't
begin to know how to fix one.
I remember from years ago that you could buy a sort of kit containing maybe
half a dozen parts, caps, large resistors, etc. If you replace all of the
parts in the bag, it fixes something like 99% of the problems that model
usually gets and prevents more problems in the future. I'm not sure if
these sorts of kits are still available though, or where to get them.
brian
8:44 p.m.
On Mon, Dec 7, 2009 at 9:23 PM, Josh Dersch <derschjo at mail.msu.edu> wrote:
_What_ flashes on/off? The screen (If so, it sounds like a beam limiter
problem, the circuitry is detecting excessive CRT beam current and
cutting the CRT off to protect it). THe power-on LED (sounds like the
SMPSU Is tripping and restarting, maybe a short somewhere in the
horizontal output stage).
Picked up an old terminal in very nice cosmetic
condition;
Funny you should post this. I was about to post about my Sony Multiscan
400PS monitor. It flashes on and off about once a second every second. I don't know much about how to fix monitors. I know
the theory, but wouldn't
begin to know how to fix one.
I remember from years ago that you could buy a sort of kit containing maybe
half a dozen parts, caps, large resistors, etc. If you replace all of the
Ah, lucky-dip servicing. Second only to board-swapping in my reckoning
:-).
More seriously, if shotgunning all those parts doesn't help, or changes
the symptoms (but doesn't fix the problem), what then? You are much
better off IMHO (as always) looking for the fault in a logical manner and
curing it. Not changing things effectively at random until somethign
seems to work again.
-tony
9:13 p.m.
On Tue, Dec 8, 2009 at 1:44 PM, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
I agree. Now what? :-)
I guess I could (should) learn monitor repair. I'll put that on the list
right after finishing up the wood shop, making a dozen pieces of furniture,
finishing the setup of my computer room, finishing the amiga 1200, amiga
2000, amiga 600, IIfx, quadra 700, 2e, 2gs, internet proxy server, laserjet
3, laserget 4100, finishing the deck, and finishing the basement.
I really need fewer hobbies.
brian
_What_ flashes on/off? The screen (If so, it sounds
like a beam limiter
problem, the circuitry is detecting excessive CRT beam current and
cutting the CRT off to protect it). THe power-on LED (sounds like the
SMPSU Is tripping and restarting, maybe a short somewhere in the
horizontal output stage).
The display flashes on and off. It turns on and wiggles for a split second
like normal, lasts half a second, then goes out. Next second repeats. It's
a trinitron tube if that matters.
I remember
from years ago that you could buy a sort of kit containing
maybe
half a dozen parts, caps, large resistors, etc.
If you replace all of
the
Ah, lucky-dip servicing. Second only to board-swapping in my reckoning
:-).
More seriously, if shotgunning all those parts doesn't help, or changes
the symptoms (but doesn't fix the problem), what then? You are much
better off IMHO (as always) looking for the fault in a logical manner and
curing it. Not changing things effectively at random until somethign
seems to work again.
9:25 p.m.
On 8 Dec 2009 at 14:13, Brian Lanning wrote:
The display flashes on and off. It turns on and
wiggles for a split
second like normal, lasts half a second, then goes out. Next second
repeats. It's a trinitron tube if that matters.
While it's doing this, check the DC output of the power supply. If
it collapses along with the image, then it's most likely a power
supply issue. This sort of behavior isn't atypical of a bad capacitor
or ten in the SMPSU.
A lot of consumer displays get tossed in the trash for exactly this
behavior.
--Chuck
9 Dec
9 Dec
7:34 p.m.
On Tue, Dec 8, 2009 at 1:44 PM, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
Does this monitor have a power-on LED? If so, what is it doing?
What are the CRT heaters doing? Do they go on and off too?
With something like this my first reaction would be to stick an analogue
votlmeter on some of the supply rails (they're often marked on the PCB [1],
anywy you might well get a service manual for a Sony monitor) and on the
CRT pins. See what, if any, supplies are pulsing on and off, see what CRT
pins are changing in voltage.
[1] I have a little Torch-badged Trinitron monitor on my XXX which has an
amazing amount of useful information marked on the PCBs. Voltages,
signals, CRT pinout, etc.
-tony
_What_ flashes on/off? The screen (If so, it
sounds like a beam limiter
problem, the circuitry is detecting excessive CRT beam current and
cutting the CRT off to protect it). THe power-on LED (sounds like the
SMPSU Is tripping and restarting, maybe a short somewhere in the
horizontal output stage).
The display flashes on and off. It turns on and wiggles for a split second
like normal, lasts half a second, then goes out. Next second repeats. It's
a trinitron tube if that matters. 
8 Dec
8 Dec
12:21 p.m.
Josh Dersch wrote:
I thought it might be HV leakage based on discussions I've seen on
this list. I've run it with the cover off and the lights off and I
can see no evidence of sparking or other visible discharge.
It still can be HV leakage in some obscure location. I've seen leakage
as small as a centimeter arcing around the FB Xmfr. If there's enough
arcing to create the crackling sound --created by the lightening speed
of electrons rushing thru the air-- you can be rest assured it's HV leakage.
=Dan
--
http://home.comcast.net/~ragooman/
http://www.midatlanticretro.org/
2:36 p.m.
--- On Mon, 12/7/09, Josh Dersch <derschjo at mail.msu.edu> wrote:
Picked up an old terminal in very
nice cosmetic condition; it works fine barring a bit of
visual "jitter" on the display -- not sure how best to
describe it. The picture is clear and sharp but
occasionally a few scanlines will spike off to the right a
bit. Coinciding with this spiking are tiny crackling
noises from inside the monitor. (Or at least it seems like
they coincide, obviously I can't verify this.)
I thought it might be HV leakage based on discussions I've
seen on this list. I've run it with the cover off and
the lights off and I can see no evidence of sparking or
other visible discharge.
Are you sure it's a "crackle" and not a high pitch chirp/squeak? Your
description of some of the scanlines jumping (but not all) seems to suggest a problem in
the horizontal circuits. Probably limping electrolytic capacitors.
Also, HV leakage is pretty common to happen right under/around the anode connection
(suction cup) on dirty monitors. Dust and dirt form a conductive path. Discharge the
monitor[1], remove the suction cup, and clean the glass around the connnection. There
should be an area of clean (non-coated) glass around the suction cup, the rest of the tube
is covered with aquadag (gray coating). Careful not to clean the aquadag off - on some
tubes it seems to be water soluble... test your cleaner (Windex, etc) gently to ensure
that it won't remove it.
-Ian
[1] To discharge a monitor, connect one end of an aligator cliplead to a flatblade
screwdriver, and the other end to the metal mounting ears of the picture tube. Slide the
blade of the screwdriver under the suction cup until you feel it hit the metal contact.
Should be accompanied by a ZAP!
8:35 p.m.
Picked up an old terminal in very nice cosmetic condition; it works fine
Make/model? Just in case one of us has heard of it and knows any stock
faults.
barring a bit of visual "jitter" on the
display -- not sure how best to
describe it. The picture is clear and sharp but occasionally a few
scanlines will spike off to the right a bit. Coinciding with this
spiking are tiny crackling noises from inside the monitor. (Or at least
it seems like they coincide, obviously I can't verify this.)
I thought it might be HV leakage based on discussions I've seen on this
THis does intiially sound like HV leakage. The spike produced when
something breaks down could well upset the horizontal scan cirucitry too.
Where have you been looking for signs of this? I'd certainly look at the
flyback transfortmer, the CRT anode capp, the CRT earthing contacts (to
the outside aquadag coating on the flare), on the CRT base PCB (the EHT
is not he only voltage that can flash over, there could well be a few
hundred volts on a CRT base pin) and so on.
Have you examined the solder side of the monitor PCB with the power on? A
cracked solder joint can produce some intereting sparks.
Could it be internal breakdown of a capactior (e.g. the 3rd harmonic
tuninc capacitor on the flyback)?
-tony
9:16 p.m.
On Dec 8, 2009, at 11:35 AM, ard at p850ug1.demon.co.uk (Tony Duell) wrote:
Ah, sorry. Don't know what I was thinking not including that :).
It's a CDC 721 (with PLATO mods). So obviously I'd like to get it
working smoothly...
With the top cover off I can get a pretty good view of all of that,
though the flyback itself is a little hard to see. In a pitch black
room I wasn't able to see anything unusual.
Picked up an old terminal in very nice cosmetic condition; it works
fine
Make/model? Just in case one of us has heard of it and knows any stock
faults. barring a bit of visual "jitter" on the
display -- not sure how
best to
describe it. The picture is clear and sharp but occasionally a few
scanlines will spike off to the right a bit. Coinciding with this
spiking are tiny crackling noises from inside the monitor. (Or at
least
it seems like they coincide, obviously I can't verify this.)
I thought it might be HV leakage based on discussions I've seen on
this
THis does intiially sound like HV leakage. The spike produced when
something breaks down could well upset the horizontal scan cirucitry
too.
Where have you been looking for signs of this? I'd certainly look at
the
flyback transfortmer, the CRT anode capp, the CRT earthing contacts
(to
the outside aquadag coating on the flare), on the CRT base PCB (the
EHT
is not he only voltage that can flash over, there could well be a few
hundred volts on a CRT base pin) and so on.
Have you examined the solder side of the monitor PCB with the power
on? A
cracked solder joint can produce some intereting sparks.
I'll check that tonight.
Could it be internal breakdown of a capactior (e.g. the 3rd harmonic
tuninc capacitor on the flyback)?
You would know far better than I :)
Thanks (and thanks for all the other responses as well)
Josh
-tony
9 Dec
9 Dec
12:01 a.m.
Ah, sorry. ?Don't know what I was thinking not
including that :). ?It's a
CDC 721 (with PLATO mods). ?So obviously I'd like to get it working
smoothly...
I have at least one pretty awful looking 721 that could yield parts,
and perhaps NOS spares.
Al should have the docs for these terminals.
--
Will
3:59 a.m.
Josh Dersch wrote:
On Dec 8, 2009, at 11:35 AM, ard at
p850ug1.demon.co.uk (Tony Duell) wrote:
Ah, sorry. Don't know what I was thinking not including that :).
It's a CDC 721 (with PLATO mods). So obviously I'd like to get it
working smoothly...
Just checked; I can't get a good view of it because the solder side of
the PCB faces an aluminum mounting plate. Couldn't see any sparks
through the 1/4" gap between the two. I took the monitor PCB out (this
thing slides right apart, very easy to service) and made a careful
examination of the soldering. No obvious cracks, it looks very good.
The flyback looks good (externally, anyway) as well. No obviously bad
electrolytics. Checked the tube around the anode "suction cup" and it's
clean as a whistle.
Thanks,
Josh
Picked up an old terminal in very nice cosmetic condition; it works
fine
Make/model? Just in case one of us has heard of it and knows any stock
faults.
Have you examined the solder side of the monitor PCB with the power
on? A
cracked solder joint can produce some intereting sparks.
I'll check that tonight.
4:01 p.m.
Hi
Get a nice new, clean and dry, piece of tygon
tubing from the hardware store.
Put one end to your ear and the other
probe around. when close the sound should
increase.
Dwight
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9:21 p.m.
On Tue, Dec 8, 2009 at 3:15 PM, Alexandre Souza - Listas <
pu1bzz.listas at gmail.com> wrote:
I thought it might be HV leakage based on discussions
I've seen on this
Best tip ever: Power it on in the dark, you'll see the blue flame :oD
That's good advice for diagnosing ignition problems cars too by the way.
brian
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