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Recent content by Aaron Newcomb

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    Macintosh Plus Flupping Logic Board

    SOLVED! It was the LAG chip after all. Upon swapping the LAG chip between the known good LB and the bad one, the problem followed the LAG. Interestingly before I figured this out, swapping the 4M RAM out for 1M RAM and leaving the Mac powered on for a minute or so, the high voltage would just...
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    Macintosh Plus Flupping Logic Board

    Yes. I am using the same cable with the known good logic board and it works fine.
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    Macintosh Plus Flupping Logic Board

    I think I might try swapping the LAG and the SND chips, but that is more of a guess based on other things I have read rather than any direct evidence for.
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    Macintosh Plus Flupping Logic Board

    Yeah. That's one of the first things I tried when I suspected the AB. I also tested all the caps and all the diodes and transistors. However, then I discovered that the AB works fine with a known good logic board.
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    Macintosh Plus Flupping Logic Board

    Another clue perhaps. With the 1M RAM in there and the resistor set correctly, I am getting the crowbar not to trip, but the voltage levels on all the rails are fluctuating about 1 - 2% back and forth instead of being nice and steady. In this state, there is no high voltage and the clock on the...
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    Macintosh Plus Flupping Logic Board

    Hello! I am trying to repair a stubborn Mac Plus with an issue on the logic board that seems to be causing the flup, flup, flup. At first, I thought it was the usual problems on the AB, but swapping just the logic board brought the system back to life. So far I have: 1. Verified there are no...
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