Greetings.

I recently acquired a nonworking Tek 465M to serve as a source of
spare parts for my main scope (also a 465M). After receiving the dead
scope, I thought it would be fun and educational and maybe even
worthwhile to try to fix it, so I would have a spare scope instead of
just spare parts. Fortunately, I have a full set of schematics, which
partially make up for my complete lack of formal electronic
education...

The scope has no trace or HV. After removing the horizontal and
vertical modules and the CRT, I discovered a blown 0.25A fuse on the
mainboard. This fuse supplies the HV oscillator with +32v (unreg),
and I verified that, yep, it blows instantly on powerup. All other
supply voltages are right on the money.

I have checked the transistors, diodes, and electrolytics in the HV
oscillator and nearby HV regulator circuitry, and there are no obvious
shorted (or open) junctions. I did discover that applying the nominal
+3.9v to the base of Q548, which is part of the HV regulator, prevents
the fuse from blowing and allows the HV oscillator to be powered.
However, it still refuses to oscillate, meaning no drive for the
transformer and HV module.

At this point, I'm kinda stuck. I think I've done my Google homework
and found lots of interesting things, such as the fact that there are
a number of Tek experts on this forum, but I was unable to find the
solution to my problem. I'd be most appreciative of any pointers.

I'll try to post the relevant schematic to
alt.binaries.schematics.electronic.

Thanks.

Steve Turner