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WPC95 coil not working
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Question
robm
I have done some power driver board swapping between MB and MM to isolate an issue, long story short, put the original MM board back in it, and the trough eject is not working - all other coils are.
There is 75V at both lugs of the suspect coil, if i ground the drive side lug, the coil fires.
If i disconnect J116 (pin 2 drives this one) and ground pin2 of J116 plug, the coil fires. If i plug J116 back in, and ground Q64 (TIP102), it does NOT fire. The coil is driven by Q68 (TIP36c), predriven by Q64 (TIP102), predriven by Q55 (5401).
I have replaced all 3 of the abovementioned transistors, with no change. When i measure voltage at the tab of Q64 (TIP102) is fluctuates and can't get a decent reading on the digital DMM - the other TIP102's around it all measure 75V.
SO, i am convinced it is a board issue (since the coil fires if i ground J116 plug, so can presume wiring to coil is fine), and the next step would be replace u7 (74LS374), which i understand to be the next step back from Q55 (5401) - is this the next best thing to try, or any other suggestions?
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