HP25C repair, help needed

[teenix]

(01-15-2019 09:53 PM)albertofenini Wrote:  One last thing,
we have left the unit with the battery connected and turned on,
after a while we have discovered the the two transistors in the PSU and the two capacitors
where very hot.
Pictured on the right is a also an HP25 board from which I have already scraped some spare parts.
Question is : how confidently can we transplant the two transistors from the HP25 to the HP25C ?
Why is on the HP25 present only a large capacitor (gray) and on the HP25 there are two ?
Can we sort of replace them ?
Anyone knows values for the PSU components specifically for the HP25C ?
Thanks a lot !!

Not sure about transistors, if they have the same markings, maybe they are the same.

The link I presented earlier has transistor equivalents hand drawn in on the circuit.

Capacitor changes probably due to circuit modifications between early and later models.

If the transistors are hot, then the power supply may not be oscillating properly and the transistors are probably passing high current through the toroid coil.

If the capacitors are hot, they are probably short circuit, so a good idea to replace them before too much more use. Check any diodes as well. The big danger is that the malfunctioning power supply might be delivering too high a voltage to the rest of the circuit.

cheers

Tony