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Losing battle against Macintosh Color Classic

GregorHouse

Well-known member
I'd need some help here with a Macintosh Color (ColoUr) Classic I bought a couple weeks ago. It was listed as not working, but when I got here a quick inspection at the logic board revealed a bad placed ROM chip, which had two pins out of the socket. Once placed properly it booted up, although without sound and a partially working screen, with artifacts and lines. I dishwashed both the analog and the logic board and that brung the sound back, but the screen was still affected. So I did a full recap of both boards and now it won't turn on. I did the analog first and, stupid me, I didn't test before recapping the logic board.

Currently, with logic board removed, the CRT makes noise and the hard drive spins. I get 11.85V and 5.00V on the logic board connector. But when I put the logic board in place it just does nothing. The 5V line drops at 0.18V. I tried isolating the pins connecting the logic board to the analog board, except for the power supply. Then I get 5.00V on the ADB port, but obviously it won't turn on.

I replaced every aluminium capacitor. In some cases I could find the exact same one and I used a higher voltage one, but same capacitance. As far as I know this shouldn't make any difference. I'm running out of ideas here, I can't even tell for sure which board is failing, any tips will be appreciated.

Thanks in advance!

 

GregorHouse

Well-known member
Ok, i found out it's the chip responsible for ADB management. It'll be helpful to know what voltage should I read from the 5V ADB pin when the computer is shutted down, but the switch is ON. Right now I'm reading 0.18V, that goes up to 5V if I isolate the logic board to analog board connection.

 

joshc

Well-known member
Any left-over electrolytic capacitor leakage on ICs, not just the Egret, will cause issues. But yes, the Egret is a critical component and you will not get a successful boot unless it works.

You can remove the Egret to completely clean underneath it and clean the pads and then solder it back on, just be careful with hot air as it's easy to cause damage to the board if not done correctly (as I did with one of my spare boards...).

There could be broken traces to repair on the logic board, take a good close look at all the traces to check for breaks, use a multimeter to test them.

Re-check your work, check all capacitors have continuity, double-check all the solder joints, on both the analog board and logic board.

If you could post some high-res photos of the boards we may be able to help further.

 

Arisotura

Active member
So I did a full recap of both boards and now it won't turn on. I did the analog first and, stupid me, I didn't test before recapping the logic board.
I had similar issues when I recapped my LC. In my case I hadn't cleaned the capacitor pads well enough. Better get them completely flat and shiny, if you haven't already.

Seeing as you're getting good voltages, your analog board is probably fine, did it have any cap leakage before the recap? I learnt the hard way that cap gunk is a real bastardy thing, gets in every nook and cranny and keeps causing trouble until it's entirely gone.

 

superjer2000

Well-known member
Ok, i found out it's the chip responsible for ADB management. It'll be helpful to know what voltage should I read from the 5V ADB pin when the computer is shutted down, but the switch is ON. Right now I'm reading 0.18V, that goes up to 5V if I isolate the logic board to analog board connection.
What do you mean by isolating the logic board to analog board connection?  Where are you reading 0.18v?

 

GregorHouse

Well-known member
Ok, it seems I panicked too early. I dishwashed the logic board again and now it works fine. Usually I put the board on the dishwasher after recapping, or after removing the caps, I don't know why this time I did it before. I guess some electrolyte may have spilled when removing the caps. It boots, the screen issue resulted to be a faulty VRAM module and also the floppy drive needed to realign heads. It's fully working now. By the way, I think it would be necessary to pin a thread on troubleshooting floppy drives.

Anyway, thanks to everyone who took time to reply.

 
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