Ok here is the problem: I get a ground short issue on the whole row 7 switch matrix. The only time it goes away is if I remove the U19 ( it has been socketed by someone else) I did not find any grounding of the wire that goes to the opto board. ( and yes , I have several LM339s that are bad on the opto board but it still displayed the ground short issue with the whole opto board removed)
I tried 3 different LM339 chips (two were brand spanking new) and also put in a brand new U20..
I cant find any shorts around the socket with my DMM.
All the tests I have done say my LM339 is fine ( the U20 tested bad and was replaced)
I must be missing something, but I cant figure out what.
anyone have any insight? Replace more chips? Could it be a problem in the U13, or even further up the line?
I tried 3 different LM339 chips (two were brand spanking new) and also put in a brand new U20..
I cant find any shorts around the socket with my DMM.
All the tests I have done say my LM339 is fine ( the U20 tested bad and was replaced)
I must be missing something, but I cant figure out what.
anyone have any insight? Replace more chips? Could it be a problem in the U13, or even further up the line?
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