68kMLA Classic Interface

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analog board fail

Posted by: mloret on 2022-05-19 16:15:38 Hey guys, I need your help. I just received an analog board that didn't work right. While the computer would beep on startup, no display on screen. I reasoned that the connections needed to be reflowed. Great, did that. Went to plug it back in and test my handy work and when I turned the power on, I saw a spark, someone popped and now it's dead and won't work anymore. There's a fuse on the board and it looks to be in tact. So two questions--any idea what I did? And how do I fix it? Any support is appreciated. 😢

Posted by: fragmax on 2022-05-19 18:37:46 Which analog board do you have?

Posted by: mloret on 2022-05-19 18:42:25 Which analog board do you have? It came out of a Mac 512k. Do you need the revision?

Posted by: Byrd on 2022-05-19 19:30:36 Time for the visual and smell test - pass your eye and nose over the board to see if you can find the damaged component. Trawl through The Dead Mac Scrolls, you might be able to get a better idea of where to look: The Dead Mac Scrolls 1992 : Free Download, Borrow, and Streaming : Internet Archive The Dead Mac Scrolls 1992 archive.org JB

Posted by: fragmax on 2022-05-20 05:27:49 I would start here (see picture). Look to see if you bridged any of your solder points you reflowed.

Posted by: mloret on 2022-05-20 10:40:57 Thank you for the tip! I did not recap and only reworked the solder joins on the connectors. But I will definitely investigate those caps and the resistor you circled. What would you recommend I look for? Clear, visible indications of burning/popping?

Posted by: fragmax on 2022-05-20 10:57:38 Like Byrd said. You can smell and see some obvious things. Those caps will burn or explode. I had the thermal resister at r39 explode apart. Recap and look around. Also check your connections from the analog board to the display and logic board. If the white plastics look burned that’s an issue. The dead scrolls are a great reference. I once didn’t get the connection right to the display and it sparked like a lightning bolt. As always be careful.

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