Classic II Conundrums

[pocketscience]

I received a Classic II with pretty classic(!) checkerboard display. Reseated ROM and RAM, same result. Recapped logic board, same result. Recapped analog board, same result. It shows checkerboard with or without ROM chips (Rev B so two ROM chips) - not sure if that's a pointer to the ROMs being bad? Both logic and analog had minor cap leakage, with no trace damage. Continuity checks around the leaked caps showed nothing sinister. Voltage checks on the analog board before recapping showed screwy 5V and 12V lines - they are now OK after recap.

Thoughts?

 

[techav]

Checkerboard usually means the 5V supply is too low to power the system. In addition to recapping the analog board, there are a few other common failures. I had to replace a mosfet and an optocoupler on my Classic to get it running.

It's been about four years since I did it, but it looks like this thread discusses the right parts to look at:

Mac Classic: Swap analog board with Classic II

'Evening all, On the right, I have an analog board from a carefully restored Classic in excellent condition. All of the capacitors were leaking. It has been fully recapped but doesn't work, and has been a bit of work to troubleshoot for a beginner. On the right, an analog board from a booting...

68kmla.org

 

[pocketscience]

Thanks, I'll take a look. I'm getting 5V at the floppy port so I don't think it's the voltage.

 

[pocketscience]

I think I stand corrected... I had the floppy and HDD connected before - when I unplugged the two of them I got a chime and no more checkerboard. Looks like the voltage is a bit flakey, even though pretty consistent reading on floppy port. I'll replace the mosfet and the opto and see if that improves things.