Color Classic Mystic VGA is missing the red from its display

[Flamingtoasters]

Hi

My Color Classic, which has been upgraded with a 575 mother board and the VGA resolution hack, frequently will stop displaying the red on its screen. Therefor, everything has an ugly blue-green tone. I already checked the video board on the CRT and replaced the VRAM on the mother board, but the problem still occurs. Anybody have any suggestions?

 

[tomlee59]

You say it "frequently" has this problem. Does it randomly come and go, or are there particular conditions that seem to provoke it? For example, does it work when cold, then get worse as it heats up? Or does banging on the unit have an effect? Things like that can provide clues as to cause.

In the absence of any information other than "it doesn't work sometimes," all one can say is that you have more investigation to do. First, perform a careful visual inspection of all relevant connectors and related circuitry. Then check things like the red video signal line. If you don't have the instrumentation to do so directly, swap red with another color (blue) and see if the problem moves.

That might do for a start. Others will soon chime in with their suggestions, if history is any guide.

 

[Flamingtoasters]

Do you mean the red wire leading from the CRT to the plug that inserts into the analog board? Or do you mean the red wire from the video board that is directly soldered to the analog board?

 

[TylerEss]

I'd guess you've got a problem in your wiring harness. I'd open up the CC and first just see if you've got crap in the connector inside the CC.

If you're lucky, there's some dirt or something in that motherboard connector causing a sometimes-open on the red video data line from the mobo.

 

[tomlee59]

Do you mean the red wire leading from the CRT to the plug that inserts into the analog board? Or do you mean the red wire from the video board that is directly soldered to the analog board?

Generally speaking, any wire that conveys the red signal is a logical candidate for investigation. However, I'd not recommend playing around with wires that go straight into the crt (aside from a careful visual inspection, and with the power cord unplugged) unless and until you've ruled out problems in the lower-voltage parts of the signal chain.

 

[Flamingtoasters]

OK

I cleaned the wiring harness that connects the motherboard, HD, floppy drive, and analog board together. I think the frequency of the red flickering has slowed down but it hasn't stopped altogether. Would the wiring harness from a 575 work with the color classic? Or should I try to clean the existing wiring harness again?

 

[Big Bird]

I don't know if you've already come across it, but there is a section in the Color Classic FAQ that answers this question. Clicky.

1.1.5 — My screen is missing one colour. How can I fix it?
You most likely have a cold solder joint on the printed circuit board (PCB) that sits on the end of the neck of the CRT. In order to fix it, you'll need basic soldering skills and tools, so if you don't have these, find a friend who does.

Pop the back shield off of the board (it lifts right up) and inspect the board closely. If you see any solder points that are dull grey instead of silver, or are discoloured, or look physically cracked, re-solder them. To be completely thorough, you should remove the old solder, apply flux to the two areas to be joined, and apply new solder, but in most cases, you won't have to do that. In most cases, simply heating and re-melting the solder is sufficient.

If the above doesn't fix it, double-check all the connections in your wiring harness, paying particular attention to the video section. If one of those connections is intermittent or otherwise flaky, it can cause weird video issues. If nothing is wrong with the wiring harness, start checking for cold solder joints on the analogue board itself. If that doesn't yield results either, try another motherboard, or different VRAM. Bad VRAM chips or bad video circuitry on the motherboard have both been known to cause video problems as well.

 

[Flamingtoasters]

Yeah, I looked at the FAQ and tried the video board repairs. I resoldered the only dull joint and it changed nothing. Also, I replaced the VRAM chips on the MOBO but that didn't help either.

 

[tmtomh]

This is a long shot, but...

I had a Mystic CC once where the red would vary from time to time. It turned out that the red adjustment pot - the red adjustment that's one of the series of little holes at the back of the analog board - was really loose from age or wear. Its adjustment was very hair-trigger, and it seemed that the slightest movement of the machine, or perhaps heating and cooling inside the machine with normal use, would make it shift ever so slight and change the red balance significantly.

Best,

Matt

 

[tomlee59]

Not such a long shot, perhaps -- good thinking tmtoh! Pots regularly develop intermittent behavior (if you've experienced a noisy volume control pot, you know what I mean). And it's easy to test for, so Flamingtoasters should do so before tearing into the guts of the thing.

First note the position of the adjustment (so that you can get back to it later). Then jiggle it, rotate it a bit, whatever and see if that has an effect. If it does, then verify that it's not a bad solder connection to the board. If it is a noisy pot, post back.

 

[Big Bird]

I just acquired a Mystic Color Classic that had a display that was entirely red. At least the green gun was not working, and perhaps the blue too (I couldn't really tell). After pulling, cleaning the contacts on, and reseating the motherboard, the problem cleared up and full, accurate color restored to the screen. It's quite a simple fix, but it might be something you've overlooked, thinking it was a monitor/analog board problem.

Also, having never attempted the Mystic upgrade myself or owning an already upgraded unit until now, is it normal for the screen to be squashed with a large-ish >1" border on the left and right edges of the screen? I haven't taken the time to open the machine up and look for adjustment pots like are on the B&W compacts.

 

[Flamingtoasters]

I did clean the mobo and wiring harness contacts with windex. Do you think windex is not powerful enough? Should I use rubbing alcohol?

 

[Quadraman]

If you have another motherboard (doesn't have to be a Mystic, it could be the original) try plugging that in and see if you still have a problem. That way you can eliminate or confirm something on the motherboard as the source of the trouble.

 

[Flamingtoasters]

I tried that but because I did the VGA upgrade, I get no video with the original color classic mobo.

 

[Big Bird]

I've never thought to use Windex. I always assumed it would leave a sticky residue. I use ~90% rubbing alcohol, and I've found it works well. Most of the luck I had, I think, involved simply the reinsertion of the board multiple times, producing sufficient friction to clean the contacts. It's one of those things that mileage will vary on, and it seems unfortunately yours may not be fixable the same way.

Another 57x series motherboard would be an easy way to try things out, but I assume you would already have tried it if you had one.