5403/D40 Scope with defective power supply



I joined this group after purchasing one of these scopes which arrived defective. Originally, the low voltage power supply was ok but the high voltage supply had a problem where the fuse was blowing.
When I fixed that, by replacing a defective capacitor, the transformer started smoking.
I then proceeded to invest quite a bit more money into buying the correct electrolytic capacitors and replacing all of those. When I was working on that, I noticed that most of the insulators behind the power supply transistors
were broken. Some just disintegrated immediately.
Of course when I tried to turn on the unit, the lower voltage supplies are no longer in spec and the regulators no longer work.
I am wondering if at this point it even makes sense to continue... How difficult is it to find replacements for the transistors? Many of the ones that seem to be a problem just say "Tekspec" in the manual.
Does anyone have an idea of what material was used for the insulators?

Thanks for any help!

Mark Vincent

The insulators are needed to isolate the collectors from ground. That is likely your problem. Replace the insulators.


Dave Hills

The metal can tabs on the electrolytic capacitors are used to complete parts of the power supply circuitry.
If the replacement capacitors do not have the same tab configuration, the circuits will not be connected
and the regulators will not function.
The fix is to add jumper wires to the PC board restoring the can tab circuits.