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(Topic ID: 251156)
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Quoted from patrickvc:Which lm339 chip controls column 7 on a WPC mpu. I’m not seeing it in my manual
none; the LM339s read the rows, your column pulses are generated by U20 (ULN2803A) this chip can be damaged by working on your machine with the power on. Just use the same matrix test procedure from pinwiki...and substitute column 7 (J206/207 pin 7) instead of the column 1 pulse at pin 1, if you have a logic probe (everyone should) then use that to determine if the column pulses are being generated.
pasted_image (resized).pngQuoted from patrickvc:I did and the entire row would activate when I would test. I changed the 2803 chip and got the ground short problems to go away but now I lost any registering on column 7.
Quoted from patrickvc:Up the chain should be u14 as a possible culprit
Please dont take this the wrong way as I don't know your board repair abilities, but it's more likely you damaged the thru hole at U20-13 than a failure of U14.
You can easily prove me wrong by measuring the resistance from U20-13 to J206-7. A reading <1 ohm is good, anything above that is not a good sign.
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