Hello,
I am working from the attached schematic (this is the power supply unit for a pinball machine).
All of my low voltage supplies (5V, -12V, 4V, 8V) are working as expected... it is the lower portion, high voltage area, that is not functioning correctly.
I have tested all transistors (Q2, Q3, Q4), and all are good. All zener's (CR10, CR11, CR12) also tested good. All diodes of the bridge rectifier (CR6, CR7, CR8, CR9) have also all been tested good. All of these components have been removed from the board and tested with the diode setting of the DMM. I have even checked most resistors and they all seem to be the correct resistance.
I have ~74VAC at the inputs as expected coming from a transformer. However, at the output (pin1) wrt GND (pin5) I have only ~13.2V. Pin3 wrt GND is 0V. The collector of Q2 (marked as 90.4V) I read ~13.8V.
I'm really stuck as to what could be causing the issue so any and all help is welcome. Could the large electrolytic C6 being bad cause this, or C8? The fuse for the 69VAC is 1/4 amp slow blow and is not blowing.
Thanks.
edit: CR10 was replaced with 1N4753A not 1N4753 but I could not find any differences between these. It is also tested good after seeing the problem.
I am working from the attached schematic (this is the power supply unit for a pinball machine).
All of my low voltage supplies (5V, -12V, 4V, 8V) are working as expected... it is the lower portion, high voltage area, that is not functioning correctly.
I have tested all transistors (Q2, Q3, Q4), and all are good. All zener's (CR10, CR11, CR12) also tested good. All diodes of the bridge rectifier (CR6, CR7, CR8, CR9) have also all been tested good. All of these components have been removed from the board and tested with the diode setting of the DMM. I have even checked most resistors and they all seem to be the correct resistance.
I have ~74VAC at the inputs as expected coming from a transformer. However, at the output (pin1) wrt GND (pin5) I have only ~13.2V. Pin3 wrt GND is 0V. The collector of Q2 (marked as 90.4V) I read ~13.8V.
I'm really stuck as to what could be causing the issue so any and all help is welcome. Could the large electrolytic C6 being bad cause this, or C8? The fuse for the 69VAC is 1/4 amp slow blow and is not blowing.
Thanks.
edit: CR10 was replaced with 1N4753A not 1N4753 but I could not find any differences between these. It is also tested good after seeing the problem.
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