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Tuesday 5 December 2017 at 07:26
I was getting a check opto 1-4 problem during test as well as ground short row 3-7. I replaced U1 and U2 (LM339) on the opto board, no change. Checking with an oscope, I have hi with pulses coming in on the green. Each of the outputs for U1 and U2 go hi when the opto is blocked. Replaced the opto ...
Source: http://pinside.com/pinball/forum/topic/taf-opto-problem#post-4107945