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Color Classic boot troubleshooting

liamoc

Member
I have a Color classic that doesn't boot that I recently acquired. The analog board seems to be working, because if I remove the logic board it powers on. Also, the logic board itself also looks to be in very good shape. Nonetheless, when I try to power it on with the logic board inserted, nothing happens.

This logic board has no CUDA switch and the power button on the keyboard appears to do nothing. Also, holding command+option+P+R and power does not cause anything to happen (no chime to indicate PRAM reset).

Despite the fact that I can see no leaking capacitors, is the next step to recap the logic board? I can't see what else could be causing this problem. I have also read that sometimes the mac needs to "soak" for 24 hours connected to mains? Can someone explain the electronics behind this because this seems bizarre to me.
 

Nixontheknight

Well-known member
By “power it on” do you mean the switch on the analog board, or press the power button on the keyboard? The color classic has “soft power” which means you must press the power button on the keyboard for it to turn on
 

joshc

Well-known member
I had a Color Classic II which did the same thing.

These have a few common issues. First of all, the logic board will need to be recapped if it hasn't been already.

Secondly, the startup circuit relies on a chip called the Egret which can be troublesome. Make sure that chip is really clean.

Make sure the edge connector on the logic board has been cleaned with contact cleaner.

I'd start with those things and see if that makes any difference before doing any more advanced troubleshooting.
 

liamoc

Member
Alright, some progress. I recapped the logic board and now it starts up successfully. The screen was entirely multiple shades of purple, though! After a few moments, the display corrected itself, but then a few moments later it became pale and washed out, with faint white diagonal lines going across it. The display is still usable but I suspected that an analog board recap might fix it.
I recapped the analog board and got exactly the same. It's hard to capture the output of a CRT in a photo, so please ignore the weird dark parts, most of the display looks like the part that looks correct. The white lines pattern is clearly in the dark part of the photo though.

Any ideas how to correct this?
 

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8tto

Active member
Hi! When the color changes during use it hints at a bad connection somewhere. If the picture is purple you are probably missing the green channel and it might be fixed by checking for cracked solders on the analogboard. So a reflowing off the analogboard and espesially the connetion to the crt-board (again) might be a solution.
Did you try to adjust the screen according to the service manual? The cut-off/voltage might be too high after the recap.
 

Big Ben

Well-known member
I can confirm, I used to have same problems.

Also, despite being glued, mine had the green signal damaged between the connector pin and wire. It’s worth checking.

For the rest as 8tto said, you need to follow the service manual on the screen calibration, but just remember to only use plastic tools when doing this.
 

liamoc

Member
I can't seem to find a hex-head plastic tool to use to adjust the display. Does anyone have any recommendations?
 

dochilli

Well-known member
Can be printed with a 3D-printer:
 

liamoc

Member
I tried doing the adjustment yesterday, but strangely, I fiddled with the contrast a bit and the display immediately corrected itself, so i guess I don't need to do the adjustments after all. Now works! Thanks everyone
 

8tto

Active member
Good to hear!
Did it change while you fiddled with the adjusment-pots or the software-controlled contrast?
([f it suddenly appeared and then suddenly disappeared, it might come back one day: it could also be worn or dirty adjustment-pots on the analogboard. But that’s for another day :-]
 
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