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Just in case it helps anyone else in the future, the ROM chip was in fact bad! I bought a for parts logic board from eBay, swapped the ROM, and I got the bong! Not out of the woods yet, though. I tried to boot to the ROM disk, and while I get past the Welcome to Macintosh screen, I never get to...

Made some progress. After deciding to reflow the caps, I noticed the C3 pads lifted immediately when heat was applied. Electrolyte corrosion was pretty nasty, apparently. Cleaned thoroughly, ran a bodge, and tried to boot the machine. Now, the machine makes sound for the first time ever! I...

I'm having a similar problem with the Classic I'm working on now, having no power on reset. Out of curiosity, if you're able to check, could you please tell me what voltage are you getting on pin 7 when you press the reset button? And what voltage across C3 on pin 8 when the reset button is...

Hey everyone -- it turns out that the reason the -12V was measuring so wrong at the floppy port was because of a rotted VIA -- perhaps it was just really high resistance and preventing the voltage from reaching there. With an ATX extension cable, I can properly verify the -12V on the J10 edge...

Hey, working to troubleshoot my simasimac Classic after doing a recap of the logic and analog boards and trying to repair damaged traces. It's coming to the point where I think I need to start measuring voltages on the board and trying to hook up a scope - it's become a nightmare of lifted pads...

I am waiting on a parts order for the opto and diodes, but I tried adjusting the analog board’s trim pot. Measuring from the analog board’s connector I’ve got 12.1, -12.1 and 5.1V. I took the 7905 voltage regulator completely off the logic board to remove the short, and connected the logic...

Okay, maybe a minor breakthrough: Haven't done too much, but noticed one thing -- not a dead short, but only 6 ohms of resistance between pin 1 (-5V out) and pin 2 (-12V in) on the 7905. That seems super low to me! I have around 0.3ohms of resistance between pin 1 of the 7905 and pin 10 (-5V...

Hi there, thanks for this! Just measured directly off the PSU's connector -- got a stable 10.57V on the 12V rail, -10.7 on -12V rail, 4.6V on the 5V rail. Seems like nearly everything is 10% off. I will check out that opto and diodes. I know there's also an analog board trimmer for the voltages...

Thanks for the replies, everyone! I ended up washing the board with soap and water because I did it before the vinegar tip. Cleaned up pretty nicely but I think my recap may have caused more problems, as I wrote in my other thread about it no longer booting :(

Hey there, definitely a newbie to this. I had a Mac classic with a good bit of electrolyte damage. No sound, couldn't boot, but came on with picture and blinking disk -- it threw a bus error when trying to boot to the rom disk. Looking at the board, it was clear that the electrolyte did some...

Hey there, doing my first Mac repair with a classic that had pretty bad electrolyte leakage, eating away the legs of capacitor C10 on the logic board, among other things. Bomarc schematics say 3.3uF/16V -- should this be a tantalum cap? It looks like there's a polarized marking on the...