Re: 7603 working .... then blank

Roger Evans


The measured +5V is sufficiently low that it would cause both +50V and +15V regulators to stop working (Q863 and Q919A have very small Vce) so a single failure in the +5V regulator can explain the other voltages being too low. Check the voltages on base and emitter of Q973C, Q985 and Q988 to see if there is an open circuit. If you don't find anything amiss in the +5V regulator then check base and emiter voltages on Q926, Q931, Q933 in the +15V regulator. Also measure the voltages across R989 and R935 since this will show how much load current is being drawn.



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