Kustom K100C-6 schem?

[Enzo]

Well, fix the +8 side first. I think the -8 tracks off it.

[Garydean]

I've been at this sucker way too long. I've had almost every component off and tested.

Almost all the readings are off....way off. For example the only place I have normal readings are at the collectors of Q910 and Q911 that's the positive rail for the preamp. All the other readings are in the negative mV range on that rail.

It's about the same with the neg rail. -38.5 on the emitter of Q915 and -37.6 on the collector of Q914. everything else reads in the negative mV range. I've replaced almost all the transistors on the main board 10 to be exact. Two resistors that were 20% over the limit and one busted up diode. Reworked 80% of the main board including all wires to and from the main board. I've played he continuity game on all the traces several times. I also tested all the transistors on both preamp boards.

I have yet to try removing the preamp boards and it's wires, apply an external power supply and load.

I figured by now the faulty component would have exposed itself thru my primitive shotgun method, which is all I know at this point with solid state circuits.

I am welcoming new suggestions or even old ones. I've put the project aside and fixed a few amps since I started this problem child..... nothing has jumped out at me.

Thank you,
Gary

[Enzo]

This is not a large circuit. On somehting like this I often just set the meter to diode test adn run down the length of the board. I check every diode and transistor. Once I have weeded out any shorted ones or obvious stinkers, then I shift my focus to resistors - specifically looking for open ones. Don't focus only on transistors, they are not the only parts that can fail.

In that power supply circuit, I see five small electrolytics. They are immediately suspicious for their age if nothing else, especially if they are tantalums. A shorted C912 could shut them down. The values are not critical, a 10uf will replace those 6.8 just fine if need be.

There should be +/-40v on R929/938, so what is on caps C909/913?

And there is a few grounded points in that circuit, is there continuity from that ground back to the main filter ground?

[Garydean]

I lifted every resistor and replaced 2. I'm after those electrolytics now, even though the ESR readings were good. All diodes tested fine as well.

Thanks for sticking with me on this one Enzo.

Gary

[Garydean]

bingo!!!! there were 2 bad tantalums on the main board totally shutting everything down. After that, one of the preamp boards was totally dead. Keeping in step with what happened, I replaced 2 tantalums and that channel is now up and working.

thank you Enzo and everyone else who stuck with me,

Gary