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Old 11-01-2007, 07:05 AM
Architect Architect is offline
Junior Member
Join Date: Oct 2007
Location: Netherlands
Posts: 14
Default Finding the error

I suspected the IC52 and I replaced it with the one in IC77. Then the problem of all the LEDs being lit constantly was gone, and I wrongly concluded I found the answer. But it just accidentally worked because I took out IC77. When I put in a new 7420 at IC77 it was back.

Since I swapped IC25 and IC41 before (with the 7400 from IC99 remember), the only thing I could think of is that IC25 was upside down which can easily be detected by checking the voltage at 7 and 14. Only then I saw 1.5 V at pin 14 of IC25 and started disassembling the machine.

Warned by Geoff, I carefully checked the board after soldering and back then I found two similar incidents. But apparently overlooking a third.
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