[chbot] Transistor for Audio Amplifier Repair

[Spencer Travers]

I am repairing someone's much loved audio amp/receiver from the 1990s and
need to find a replacement transistor. It is a 2SD1762DEF TO-220 NPN
bipolar power transistor. Some datasheets say it's 50V, 3A rated. There are
some ebay listings for this part.

Does anyone have something local and suitable or some pointers? I do have a
service manual with schematics. If anyone's interested, here is a  link:
https://drive.google.com/file/d/1DhsyuLpafuNbXBOhnIgTRilbyw64tCRr

Q701 is the dead transistor, located at grid 32B in the schematics.

This transistor is used to create +15 V from the +40 V rail. It looks like
the audio input selector IC401 shorted +15 V to -15 V and took out the
transistor along with a couple of traces on the PCB. R405 & R406 and
surrounding traces were destroyed. The good news is that injecting +15
volts from a lab PSU to where Q701's emitter was connected seems to make
the amp work OK.

I had thought of using a 7815 voltage regulator but I think the input
voltage would be too high. I do see some devices on ebay and may have to
resort to that.

I guess another option would be to add a separate transformer, rectifier,
and voltage regulator to get 15 V, but I would rather avoid that.
Unfortunately there are no suitable lower voltage taps on the transformer.

Spencer
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.ourshack.com/pipermail/chchrobotics/attachments/20230219/9354ad2e/attachment.html>