7603 15+ rail dead. Options?

Dave Voorhis

I’m bringing a 7603 back from having released its magic smoke. The +15 volt rail is dead, the 0.1 ohm current sense resistor R935 having gotten hot enough to have unsoldered itself and fallen out. Q926, Q931, and Q936 are defective. Q933 and relevant surrounding components appear to have survived.

A replacement Q931 (2N5189) is easily and cheaply found, but a new replacement for Q936 (2N2919) costs about twice what I paid for the oscilloscope and Q926 doesn’t appear to have a specified substitute — though I presume any small NPN transistor capable of handling 60 volts or so would be fine.

Is there any good reason why I can't simply obtain +15 v from a 2 amp 15 volt regulator chip — like an L78S15CS — and ignore the +15v sense line?

I’ve verified that the ‘scope essentially works with +15v provided by my bench power supply and draws a little over 1 amp.

For reference, I’ve linked an image of the relevant page from the power supply schematic here: http://www.armchair.mb.ca/~dave/tmp/Tek7603_plus15v.png

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