Breadboard resistance

[Billathome65]

Hi I'm currently trying to repair a Kenwood KA-76 Amp I stupodly damaged and need to check a risser board to see If there is a problem with that.

This is a schematic of the board showing 50V but also 20V

If I put it into a breadboard to test what rate resistors would I need to use 10KOhm?

Cheers Bill

[Billathome65]

[eccerr0r]

Not clear what you're trying to accomplish here... normally I don't use a breadboard and just test while the device is installed, or is it because it's in an inaccessible location?

[Billathome65]

No i'm trying to track down a short that only shows when the board is soldered onto the main PCB trying to work out if its an issue on the main board that shows up once connection is made to the riser or if its the riser itself that has the problem. The riser is a pain to solder in and out again so want to try to check it off the board as if thats possible?

2 resistors burnt out on the rise on the 50V trace.

[eccerr0r]

usually resistors go open when they fry so it should be fairly quick to just see if any semiconductors shorted...running these custom boards out of the original device is quite a challenge...

[Billathome65]

Cheers eccerr0r

[Billathome65]

Cheers. I tracked down the short to one of the transistors.

The strange thing is it was reading fine in circuit but I noticed that when measured in the TC1 tester it read as a diode? However the other transistors read as transistors, so this was strange.

As it measured fine I reinserted and when I checked resistance it was showing a short between legs but not off board?

I ensured there was no solder bridge then replaced with another and the short disapeared.

Not had chance to reinstall the board yet due to a couple of fractured ribs but I hope when its reinstaled on the main board there is no constant bright light on the dim bulb tester.

[eccerr0r]

I suspect bipolar junction transistors can short out one of the two junctions and have the other one still work like a diode, so it's possible universal testers may identify it as a diode.

Still suspicious, usually these tiny to92 transistors even when shorted won't cause power fuses to burn...thing would have to pass quite a bit of current to do so and they weren't designed to do so...