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Mac Plus checkerboard screen, no audio after analog and logic board recap

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I've been having A/V problems for some time now, I asked people on r/VintageApple and they said I should recap logic board. I already replaced all cylindrical capacitors on the analog board and a professional replaced the capacitors on the logic board, but alas, there wasn't any change, I still get this checkerboard on startup and there's no sound at all (except some occasional faint screeches). I am getting really desperate for solutions because this is a very specific problem that has not been (probably) documented yet. I really want to make my Mac Plus work again, but anything I've tried did not help at all (I guess I don't have to worry about caps anymore...). I have little experience with electrical circuits but from what I understand, picture is relayed through RAM, so maybe the RAM is broken? Although it shows 2,560K installed which is in fact the amount of RAM installed... Maybe there's a bad contact on J4, I really don't know. So, people of M68kmla please help me!



P.s. along the things I already did is checking the voltage, it was a bit off and I did set it to 5V, but alas, no difference.

Edited by Shymon184
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15 hours ago, dochilli said:

Could be a problem with the ROM, especially if you hear no chime. Take the ROM chips out, clean the contacts and reseat them.

Some connectors on the Analog Board can be broken. Resoldering may help.


I cleaned the ROM chips and I already resoldered J4 pins on the analog board some time ago, but I got these results: I still got the same checkerboard screen, but the speaker did a little “thud” sound when it switched from checkerboard to the gray screen and the speaker screeched a bit when the diskette icon appeared. I have very little experience with electronics but this makes me think that certain parts of the circuit are not getting enough voltage to operate which results into checkerboard and silent speaker.

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