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Macintosh 128k issue

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It could be any number of issues, but one thing that MUST be done to any 128k/512k/Plus is a reflow (with a touch of fresh solder) to the the areas with connections on the analog/sweep board as well at the logic board. This is a pic I made to help. Its for a Plus, but its nearly the same.


Typically though a line top to bottom is a deflection issue. This can be the result of a bad solder joint to the deflector at the red or green wire (I forget which). So I would say to start with solder joints while looking for any damage. If you can pull voltage readings, I would do that as well. If it still fails, then individual components need to be looked at.

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I agree, remove the white protection of the Analog board and look at the four pins where the white connector is plugged in.


usually, the top one is the first to go (the connector is usually burned also)


I will recommend to remove old solder first, then put new one.

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Going based on your image, I'd check out these red highlighted joints and check for any cracks and\or resolder them. They're looking a bit iffy to me in the pic, often times a straight up pin in a shallow pool of solder like the 2nd from the bottom left will be one of the first joints to crack. Using a bit of flux can help with that. http://i.imgur.com/mH2TE6l.jpg

Edited by Compgeke
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I usually reflow all of the solder joints on these 128k/512k/SE analog boards with fresh solder. Takes about half an hour, and then you can be sure it will not happen again. I began shotgunning them after I spent few hours on a 512k board that worked for half an hour then the CRT started acting up and cleared up when twisted the analog board.

There is usually no need to remove old solder, just add new. Use some flux if the solder is not flowing like it should.

I would resolder and check the J1/L2 area first.


Also check the R1 (220 ohm).

I would also replace the C1, as it is the old 25/35V electrolytic type and these go bad and cause similar problems. The proper replacement is 3.9uF 100V Non Polarised HF Film capacitor.

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