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Macintosh All-In-One Disaster

mikerofone

Member
I replaced the capacitor at C1, no change. Felt like giving up at that point. Then I replaced the 4N35 at U3...and it came to life! I'm also getting the proper voltages on both the 5v and 12v lines, and the floppy drive is back to normal. I want to thank all of you for your help during this stressful ordeal. I hear the floppy drives tend to go bad with age (eject seize up, broken gears), so I don't even plan on using it. I just ordered a Floppy Emu Model C Bundle from BMOW and a keyboard cable for the M0110 keyboard which I need.
Hi Davey and others,

thank you for posting this! I got a Mac Plus recently which booted once or twice with a very wobbly screen, but then failed to generate anywhere close to 12/5V. The voltage was kind of randomly stuck between 8-10V on 12V, and adjusting the regulating resistor no longer had any effect. Replacing the optoisolator with a 4N35 I found in an Arduino starter kit fixed it as well! No more wobbling, and I was able to dial in roughly 12.2V and 4.9V. Not perfect, but still within spec (Apple repair manual says up to 12.7V is OK for the 12V rail). I have touched up all solder joints on the analog board, but if I wanted it to be any better I probably need to do a full recap.

I wasn't able to find much information on the optoisolator in all the various repair manuals, and the "voltage adjustment not working" behavior was not mentioned in any of the PDFs floating around posts like these. So your post was the missing hint I needed!

Cheers
mikerofone
 
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