> > Since "they never did provide BASIC" then there was *always* "no ROM
> > BASIC." That's like stopping the machine with a message stating "no
> > printer." Why not display something understandable to a common user,
such
> > as "no bootable device?"
>
> Because INT 18h doesn't check for bootable devices. It is the entry to
> ROM BASIC. It may well be that the most common time that it is called is
> from the bootstrap after both floppy and hard disk boots have failed, but
> that doesn't mean it's the only time it can be called.
Tony, are you simply being obstinate here, or didn't you see the above
reference to "common user?" Do you think "common users" -- not to be
disrespectful to plain old computer users -- read BIOS listings???
What I mean to say is: Suzy Six-pack, who ekes out a living typing up MS
Word documents, doesn't know shit about the internals of the machine she
uses.
> Actually, one thing that really annoys me are error messages that don't
> describe the real problem, but only the most likely cause. I need to know
> waht's really going on so that I can fix it. Odd, that....
Yes, and even more odd is that you fail to see that "no bootable device" at
power-up actually does describe the problem, whereas "no ROM BASIC" does
not, since the system in question would never call INT 18h if a bootable
device were available (unless some insane programmer called it, and I
seriously doubt that you can show me a commercially available program which
does this).
Glen
0/0
From: Eric Dittman <dittman(a)dittman.net>
>The third-party controllers were most popular on the Model 1, since the
stock
>FDC was SD. There were a few third-party controllers for the Model III
and
>the early Model 4, but they weren't as popular as the 1793 was more
capable.
>The stock Model 1 FDC also had reliability problems that lead to
third-party
>data separator plug-in circuits.
Yep, the M1 data sep was the 1771 internal and that was at best terrible
and WD would tell you that. That lead to the Piggyback card to at least
add a decent data sep. The 1793 came later but was very desirable
as the 35/40track Single sided FD100 or SA400 drives were tiny storage
wise.
Allison
I realise this may not be the best forum to ask this question, but the
emulator newsgroups seem to be pretty much dead.
I'm updating an Apple ][+ emulator that I wrote back in 1994. I would
very much like to emulate a printer interface card, such as the Grappler+,
but I never owned a printer for the Apple ][+ I still have at home, so I
don't have a printer interface card that I can study.
So...I was wondering if anyone on this mailing list happens to own an
Apple ][ with a printer interface card like the Grappler+, who would be
willing to dump the ROM(s) and provide me with details of the I/O locations
used.
I realise some of you may be against distributing ROM code on the basis of
copyright (I personally feel that discontinued products don't deserve
copyright protection, though I realise the law says otherwise). If nobody
is willing to provide me with ROM code for a printer interface card, I'll
settle for a description of the I/O locations and any other information you
can give me on the operation of the printer interface card, and I'll write
my own "clean room" version of the ROM instead.
Regards,
Philip
On Oct 7, 16:50, ajp166 wrote:
> Beats me what that drive is. This is a group for hardware over 10 years
> old.
> If it is that old you likely going to be fixing it yourself.
> -----Original Message-----
> From: CByrd87043(a)aol.com <CByrd87043(a)aol.com>
> To: classiccmp(a)classiccmp.org <classiccmp(a)classiccmp.org>
> Date: Sunday, October 07, 2001 3:48 PM
> Subject: Hard Drives
>
>
> >I have a Hard Drive model P1200-2af. I need to know where can I send it
> to
> >get it fix or replace. It just stop working.
It's a nothing-special 1.2GB IDE drive with a bad reputation, made by JTS.
JTS are no more, so the only likely option is to replace it with a
Seagate, WD, or whatever.
JTS were famous for, amongst other things, buying part of Atari from the
Tramiel family, laying off a lot of staff, and then selling it to Hasbro
shortly after being de-listed by the stock exchange and shortly before
going bust in 1998.
--
Pete Peter Turnbull
Network Manager
University of York
Beats me what that drive is. This is a group for hardware over 10 years
old.
If it is that old you likely going to be fixing it yourself.
Allison
-----Original Message-----
From: CByrd87043(a)aol.com <CByrd87043(a)aol.com>
To: classiccmp(a)classiccmp.org <classiccmp(a)classiccmp.org>
Date: Sunday, October 07, 2001 3:48 PM
Subject: Hard Drives
>I have a Hard Drive model P1200-2af. I need to know where can I send it
to
>get it fix or replace. It just stop working.
>
> Now, it occurred to me that you may have thought "ohhh, DLT drive, 10 to 20
> GB per tape." and if that was the case I hate to disappoint you. You'd
> would need to find a TZ89 rather than a TZ85.
The 20GB uncompressed drive is the TZ88/DLT4000.
--
Eric Dittman
dittman(a)dittman.net
Check out the DEC Enthusiasts Club at http://www.dittman.net/
> > So now I'm left with two questions:
> > 1) Has anyone got any source code for the WD1770? 6502 ASM, C, anything.
>
> The 1770 is pretty much compatible with the other Western Digital FDCs.
> The TRS-80 model 4 uses the 1793 (very similar in software), and the
> sources of LS-DOS 6.3.1 are on the web somewhere (Tim Mann's page?).
> That's Z80 assembly language.
The later (gate array) TRS-80 Model 4 systems used a 1773 FDC, which was
compatible with the 1793. The 1770 and 1773 were compatible, differing
only in the logic states of some of the lines, but it's been so long
since I've used either I can't remember which pins were different.
The 1770/1772/1773 had both the data separator and write precompensation
built-in. They are 28 pin devices (the 1793 is a 40 pin device).
--
Eric Dittman
dittman(a)dittman.net
Check out the DEC Enthusiasts Club at http://www.dittman.net/
> > The later (gate array) TRS-80 Model 4 systems used a 1773 FDC, which was
>
> Interesting. The older model 4s (like mine) have a 1793 -- the floppy
> controller board is indentical to that in a model 3. I'd assumed they
> used that board in the gate array versions as well.
>
> Maybe they did (in the early gate array machines), and then changed to
> the 1773 for the last ones. I don't see any reason why that couldn't have
> been done -- as you said the 1773 and 1793 are pretty much compatible.
The early systems weren't gate array systems. The gate array Model 4
and 4P systems had the FDC and RS232 integrated on the mainboard. If
you have a separate FDC and/or RS232 board then your mainboard is not
a gate array model.
--
Eric Dittman
dittman(a)dittman.net
Check out the DEC Enthusiasts Club at http://www.dittman.net/
> > The ULA does a lot more than handle the display ;>)
>
> CPU clock generation (which would be useful). Address decoding (which I'd
> want to modify if I was changing the amount of RAM).
Very interesting -- how much RAM are you talking about adding that you have
to modify the address decoding?
> > Of course not ;>) But a ZX81 kit is still faster than starting from
> > scratch.
>
> Is it? It's not going to take long to wire-wrap a clock circuit and
> address decoder, and stick in the Z80. It depends _very much_ on how much
> of the ZX81 you want to use...
Which in turn depends on what the intended use of the finished device is.
Since I want a "general purpose" computer the ROM BASIC functions are very
convenient, and fast if called directly. Other applications of the Z80
would not need this code so a quickie Z80 board would be fine.
> > Try desoldering the RF modulator from a ZX81 board ;>)
>
> Well, I had never tried to do it before, so I grabbed a ZX81,
What, do you have a pile of these?
> unscrewed
> the case and attacked it with soldering iron and sucker.
>
> What's the catch?
In the US versions which have 3 thin wires, they sometimes become brittle
and break.
Tony (and others), a question: in your opinion, which microprocessor was
the most well-designed (even if not implemented)?
Glen
0/0
On Oct 7, 17:14, Alex White wrote:
> Hey all UK people - do you know of a source for 6502s (and related
support
> chips, such as the 6522) within the UK?
Farnell still list the CMD version, G65SC02, catalogue number 562-750, and
the Rockwell R65C102, cat.no. 388-488, though the Rockwell parts is listed
as "available until stocks are exhausted". They also list several
varieties of 6520, 6521, and a 6545 (Rockwell version of 6845 CRT
controller), but I know of no suppliers for new 6522s.
--
Pete Peter Turnbull
Network Manager
University of York
I wanted to bang out a quick thing involving bussed lines (an LED display
for a Dragon's Lair game, if you're curious). I thought it might be
quick to do with veroboard as opposed to point-to-point wiring. I want
to make a prototype before considering burning a board (since that's a
weakness I have at the moment anyway - lack of knowledge about layout
tools). The problem is that I haven't seen veroboard for sale in the
States, only the U.K. and perhaps Western Europe. Here, we have
lots of modular prototyping board, but it's not easy to use when you
have a lot of parallel connections (like a data bus).
Are there any sources on this side of the pond? If not, how much does
a sheet of about 6"x9" cost? If it's too expensive to buy and ship, I
have several square feet of plain blue perfboard I got from the Micro
Center when they put all their hobbyist stuff on remainder, and I'll
build it from scratch.
I went to school in England in 1985 - New College, specifically, down the
street from Blackwell's Books. I spent many hours there absorbing
everything I could about hardware hacking (not having the budget to _buy_
the books - the Turf Tavern was closer to the gate ;-) I remember a
couple books with do-it-yourself projects using veroboard. Now I wish I'd
gotten more books and less beer (but it was _great_ beer) :-)
Any veroboard pointers?
Thanks,
-ethan
__________________________________________________
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Tony Duell wrote:
> Since they never did provide BASIC they had to make INT 18 do something
> (remember an application program could, in theory, call that interrupt).
> Since that interrupt should have entered ROM BASIC, the most sensible
> thing to do was to print that there was no ROM BASIC and then halt the
> CPU.
Since "they never did provide BASIC" then there was *always* "no ROM
BASIC." That's like stopping the machine with a message stating "no
printer." Why not display something understandable to a common user, such
as "no bootable device?"
Glen
0/0
On Sat, 6 Oct 2001 at 01:25:28 +0100 (BST), ard(a)p850ug1.demon.co.uk (Tony
Duell) said:
> > BTW, I also need some info on the Intel 8271 disk controller - I've got
two
>
> I would not do a new design using the 8271. The chip is fairly hard to
> find now, and there are machines that _need_ them (like the old Acorn
> Systems).
OK, then. One 8271, starting bid $100 - just kidding :-)
> In fact, I'd probably use one of the all-in-one PC floppy controller
> chips unless there was a very good reason not to. Add a crystal and
> perhaps some cable driver chips. That's all...
Is "I don't know any suppliers for PC FDCs" a good reason?
Farnell Electronics don't seem to sell them, nor do Maplins, Electrovalue,
ESR Electronics or any other supplier I know. Care to tell me where I can
get them?
> > of these little devils and Intel's datasheet makes absolutely no sense
at
> > all. I've also got a Western Digital WD1770-PH 00-02 that I might be
able to
> > use instead. First of all, which is the better controller? The 8271 or
the
> > 1770? Also, is it possible to overclock a 1770 or an 8271 like you can a
> > 1772?
>
> Oh, use the 1770. It does double density (MFM) for one thing (the 8271 is
> single-density only). It also require many fewer support circuits I
> think.
OK, then. The 1770 it is.
> The 1770 and 1772 are closely related (the difference being the step
> rates the chips can produce). I would guess that the 1770 can be
> overclocked, but I've never tried it.
I think I'll keep it running at the normal speed (8MHz). But the machine
will have a 16MHz oscillator and a divider, with a few jumper blocks for
clock speed selection (8 and 16MHz for the FDC, 1, 2 or 4MHz for the 6502
and support circuitry). I've got two Western Design Center W65SC02s (14MHz
6502s! Woohoo!) to play with, plus a Synertek SY6502A (the 2MHz one), two
W65SC22s (10MHz WDC 6502s) and two Synertek 6522s (1MHz).
So now I'm left with two questions:
1) Has anyone got any source code for the WD1770? 6502 ASM, C, anything.
2) Has anyone got a schematic for a fairly half-decent 16-colour (or
better) video card that can be modified to work on a 6502? I've had a look
at the NASCOM schematics but I've heard Bad Things(tm) about the NASCOM
video system. Aparrently Gemini and a few others produced colour video cards
for the NASCOM. Anyone got schematics for these? Graphics would also be nice
(the NASCOM video system is text only).
BTW, I'd like to avoid obsolete components if that's at all possible.
I've got a Hitachi HD6845 but if the 40-odd page datasheet is anything to go
by, it's a real dog to use... And it only works in monochrome. I have got a
MOS Tech 6568(?) VIC-II, the same one used in the UK Commodore 64. The PSU
for this C64 is fried, took out some of the support components with it.
TIA.
--
Phil.
philpem(a)bigfoot.com
http://www.philpem.f9.co.uk/
> The 1772 and 1770 were designed specifically for use with the 5-1/4" units,
> though that's not necessarily what their use today may be.
>
> I've never seen the 1773 in the flesh, though I've got a data sheet somewhere
> (though I've managed to hide it somewhere). The three chips are all similar,
> though not identical, in that they have the same data/clock separator circuitr
> and write precomp circuit. However, the 1773 lacks some signals that are on the
> 1770/72, thereby rendering it less "dedicated" to 5-1/4" drives. The datasheet
> did, IIRC, specifically indicate that they're all similar in commands, etc,
> though the timing parameters differ somewhat in that the 1770 is slower than the
> otherwise identical 1772 in terms of its step rate settings. If I could lay
> hands on the 1770/2/3 datasheet, I could tell you which pins differ and in what
> sense, but ...
The 1773 is also dedicated to 5.25" drives. Your email jogged my memory, and
indeed the difference between the 1770 and 1773 was a couple of different
signals. I've used the exact same code on both of them. From a programming
point of view they are the same. I don't think there was a version of the
1773 with the faster step rates like in the 1772.
> If somebody's got a 1773 and wants a 1770, I'll happily swap 'em, just so I have
> one in house.
If you find a gate array TRS-80 Model 4 then you'd have your 1773.
--
Eric Dittman
dittman(a)dittman.net
Check out the DEC Enthusiasts Club at http://www.dittman.net/
On Oct 7, 2:17, Iggy Drougge wrote:
> >> >If it's another 40 pin chip, then that's the custom ULA chip that
> >> >includes most of the glue logic.
> >>
> >> Is that like a lot of 74138s or something?
>
> >It's rather more than that (I assume that's the address decoder part,
> >which is in the ULA). It also handles the DRAM timing, most of the video
> >display, and so on.
>
> I thought one of the selling points of the Z80 was its built-in ability
to
> handle DRAM. But perhaps it's lacking the 6502's ability to easily share
> memory with other devices by only doing memory accessing every second or
> fourth cycle.
The Z80's special ability in handling DRAM is merely the presence of an
on-board counter which increments once in every instruction cycle, and
which is output onto the address bus once per instruction. This is only
part of the requirement, however (see below). The refresh counter means
the chip is guaranteed to cycle through the addresses (with no omissions)
in a given period. This is exactly what you need for DRAM refresh. Of
course, if you have a video circuit accessing the same DRAM, it too will
cycle through the address range (or part of it) and achieve the same end,
so the Z80 refresh is only a useful bonus if you don't have video accessing
your DRAM. Anyway, it's only a 7-bit counter, which is fine for 16Kbit
DRAM but not for most 64Kb devices.
The downside is that a Z80 uses the clock in a different way from a 6502.
A 6502 does some things on one half of the clock cycle (like accessing
memory to read instructions or read/write data) and other things (internal
operations) on the other half cycle. During the half-cycle when it doesn't
need memory access, it releases the bus, leaving it free for use by other
devices (eg video). A Z80 uses successive cycles (of a faster clock)
instead of alternate half-cycles for different purposes and there is no
clock state when it's guaranteed not to be using the bus. However, there
is one (whole) clock cycle when it doesn't need the bus, and that's the
refresh period; it's just more complicated to decode that than to just use
the phase of the clock (high or low) to enable your video access (or
whatever). It's also less suitable than the 6502 since Z80 instruction
cycles vary in length and therefore the interval between refresh cycles is
not constant. The interval between successive half cycles of a 6502 clock
is (usually!) constant.
I said the refresh was only part of the requirement. That's because DRAM
normally splits the address into two parts, row addresses and column
addresses, to address a given cell in the memory matrix. Usually these two
parts of the address are multiplexed onto the same pins of the IC.
Therefore, on the first part of the memory access cycle, you put the row
addresses on the pins and signal this to the DRAM with the /RAS (row
address select) signal. The IC latches these address bits internally, and
after some time period, you turn off /RAS, replace the row address bits
with the column address, and apply the /CAS signal. Neither the Z80 nor
the 6502 have any special feature to simplify this (unless you count the
fact that you have two clock phases per memory address on a Z80). So in a
Spectrum, ZX81, etc, the ULA takes care of the address multiplexing and
RAS/CAS timing.
> But what does glue logic really mean?
Just slang for the assorted logic that does address decoding, signal
buffering, RAS/CAS generation, etc. In a typical system with, let's say,
ROM, RAM, processor, some I/O ports, perhaps a DMA device, each section
that connects to the address/data bus (and perhaps the control bus too, if
DMA is involved) would have its own set of buffer ICs, each being enabled
only when the relevant section is accessing the bus. The glue logic
includes all the decoding/multiplexing of the address and control signals.
If you think of a system as CPU, RAM, ROM, I/O ports, then the glue logic
is all the extra circuitry you need to "glue" them together into a working
system.
> Couldn't Sinclair have socketed the BASIC? It must have been a lot of
work to
> piggy-back it onto each imported Spectrum, unless the customers had to do
it
> by themselves.
Sinclair never used sockets if they didn't have to, for reasons of both
cost and reliability. If there was a special Sinclair-original ROM for
Scandinavian countries, I would have expected that to be factory-fitted
instead of the standard ROM. It's possible they retrofitted something like
that -- it might be cheaper to piggyback a new ROM instead of removing the
old one -- but I would guess that what you have is something done by the
original owner, in order to have both systems. Sinclair would be most
unlikely to fit something as extravegant as a switch.
--
Pete Peter Turnbull
Network Manager
University of York
Hey folks. I've got four or five SGI Personal Iris machines
here...4D20, 4D25, and 4D35, in various configurations and in various
states of operability. I also have three Macintosh Quadra 950s. I
offer them for free to any interested party for pickup in Laurel, MD
within the next two weeks or so. I am moving, and they need to go.
In addition, there's a list of [non-free] stuff that I have available
at http://www.neurotica.com/available.html.
-Dave
--
Dave McGuire
Laurel, MD
While visiting my electronics shop, I found a collection of largish cards
(circa 15?25 cm?) made by WANG. There were at least two video cards - one IBM
mono emulator card and one low-res cards. There was another card with two BNCs
and a switch, could be a grpaihcs card, too. There was a winchester
controller as well, and some card which I couldn't identify.
If anyone's really interested, I'll see how much he wants (probably very
little, they're sold as scrap).
--
En ligne avec Thor 2.6a.
G? med i SUGA, Swedish Usergroup of Amiga!
WWW: http://swedish.usergroup.amiga.tm/
BBS: 08-6582572, telnet sua.ath.cx, port 42512.
In a message dated 10/6/01 3:35:56 PM Pacific Daylight Time,
ms(a)silke.rt.schwaben.de writes:
> 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
Mu metal should be easily scroungable. It is the shielding on old large
graphic monitors, Convergent "N"gens and many other pieces of electronic
gear. Often found around CRTs and CPUs. Tektronix used a lot of it.
It is soft and usually a dull gray although sometimes silvery. Occasionally
it shows a crystal type surface. It is magnetic and not a good conductor.
It is expensive new. We got up to $5 per pound for it, scrap, at one time.
Paxton
Astoria, OR
On another list someone mentioned that a PDP11 ran at about the same
speed as a 486-66.
I don't have a 486-66 but do have a PDP11/34 in the garage so I
suggested that if a 486-66 could be found we could have a race.
I tested the capacitors on the weekend and they were OK, still need
to test the RL01 drives and get them hooked up.
>From the cables in the cabinet and the terminator on one of the drives
I'm guessing that they are daisy chained.
A few questions remain.
What would be the best way to test the Power supply it is currently
off the chassis, does it need to be connected for testing?
Any suggestions for a fair race?
Recent additions: Unisys PW2 (Unisys ICON NETWORK), Microcom (apple
clone), SHARP PC4500
Collector of Vintage Computers (www.ncf.ca/~ba600)
Hi,
I'm building myself a 6502-based single-board computer, with the aim of
running it off a 4.8V NiMH or NiCad battery pack. But I've got a problem. I
need a programming language for it. Aparrently there were many BASIC
interpreters sold for the Synertek SYM-1 (aka SY-VIM-1), MOS KIM-1 and
Rockwell AIM-65. Anyone know what happened to the companies that produced
these? Ideally I'd like the source code for a 6502 BASIC interpreter, but
binary code would be OK too. The SBC will communicate via a small LCD panel,
RS232 (so I can hook it up to a "dumb terminal") and will have a hexadecimal
keypad and an optional hard drive, too. Anyone care to make any suggestions
(or submit some code)?
BTW, I also need some info on the Intel 8271 disk controller - I've got two
of these little devils and Intel's datasheet makes absolutely no sense at
all. I've also got a Western Digital WD1770-PH 00-02 that I might be able to
use instead. First of all, which is the better controller? The 8271 or the
1770? Also, is it possible to overclock a 1770 or an 8271 like you can a
1772?
I'd love some schematics and/or some source code. I really don't fancy
disassembling Acorn's 8271 DFS and Watford Electronics' 1770 DFS...
Thanks.
--
Phil.
philpem(a)bigfoot.com
http://www.philpem.f9.co.uk/
We've had the ongoing debate of "build a ZX-81 kit or leave it in the box",
but one aspect of classic kit building I have a question for the group
about is, what about stuff that we built ourselves 10+ years ago that
still works, but might need some touch-up. Specifically, I have several
things (a TVT-6, a Cosmac Elf, a homemade arcade button panel for playing
Space Invaders on a PET, a 2-char LED display for the PET, etc.) that
I made when I was a teenager. They still work, so it's not a question of
repair. It's an aesthetic thing - my soldering skills were much poorer
when I was 13. I'm debating re-soldering these items (and risking breaking
them) or leaving them the way they are a) because if it works, don't
screw with it, and b) it's a snapshot of my own context in the greater
historical framework.
I took history and archaeology in school; I have a strong aversion to
modernizing artifacts. When restoring pots, statues, mosaics, etc.,
an archaeologist tries to never restore an antiquity in a way that can't
be reversed (they use water-soluable glue made from fish scales to move
mosaic fragments, for example). Also, when modern materials are used, no
attempt to make it resemble the ancient material is made - quite the
opposite - it's plainly and intentionally modern looking so ever a
casual observer can't mistake it for the missing original. When my
advisor restored the bed of a large monochrome mosaic near Isthmia, he
threw several modern coins into the concrete bed so that future
excavators would know that it wasn't ancient concrete.
So re-soldering my TVT-6 makes it look nice, but dilutes the fact that
it was originally built in the 1970s, just as much as using modern
ICs does. Do people have an opinion about this? Am I just stuck on
the horns of a false dilemma?
-ethan
__________________________________________________
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NEW from Yahoo! GeoCities - quick and easy web site hosting, just $8.95/month.
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>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).
Knowing NOTHING about the unit you are working on... two things pop in my
mind from my TV/VCR repair days.
1: Is it possible the controller on the back of the tube is loose? When
you tilt the lid (and from what I gather, the tube with it) back into
place, maybe the board is shifting from the change in weight position.
2: Is there a cable or wire that is getting pulled on when you close the
lid? Maybe one of them has a bad solder joint, and the joint stays
properly closed when the lid is open, but when closed, gets pulled (or
pushed), and breaks the connection. Have you tried, while the unit is
open, to jiggle any wires that might be effected (obviously, don't do
them with your hands, use a non conductive spudger or similar tool...
wouldn't want you to kill yourself by grabbing the wrong wire)
Again, I know NOTHING about the unit you are working on, so these were
just shots in the dark thinking maybe something will help.
-chris
<http://www.mythtech.net>
On October 6, LFessen106(a)aol.com wrote:
> Hey Dave, can you hold onto a Quadra for me?
Sure, if you can grab it before I move...end of October...
-Dave
--
Dave McGuire
Laurel, MD
What you need is Mumetal which is a MAGNETIC alloy.
Lacking that distance helps.
Having built numrous O'scopes over the years the problem of
transformers radiating magnetic fields are well known to me.
Allison
-----Original Message-----
From: Adrian Vickers <avickers(a)solutionengineers.com>
To: classiccmp(a)classiccmp.org <classiccmp(a)classiccmp.org>
Date: Saturday, October 06, 2001 3:39 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
>
