5150 combo problem

[Anti-Hero]

Hello

I was working on a friends 5150 combo, I have never worked on a lay out like this, and after i put it back in the box, 4 of the pre amp tubes and the channel select lights arn't turning on, the phase inverter and power tubes are lighting up, but thats it, and no sound is coming out. I'm at my wits end here, i tested every single resistor and capacitor on the board, and nothing was showing an open circuit.

If someone has any ideas I'm all ears

Thank you

[Ronsonic]

Probably a low volts DC supply for the tube heaters and switching. Do check the stupid fuses and the solders. Peavey used to never have bad solders.

Oh, and I hate working on those, too.

[Enzo]

Look at the schematic, the preamp tube heaters are in series. Two across the -23v and the other two across the +23v. ANy one open tube will darke3n its mate.

But you have them all dark, plus no indicator lights. That indicates to me you have lost your +/-25v rails. I'd be checking those two fuses, F3, F4, 1A fast blow. And there ought to be about 18VAC on BOTH ends of each fuse.

ALWAYS pull a fuse from its clip and measure it with an ohm meter. DO not rely on visual inspection, and if you ohm them out while still in their clips, you risk false circuit paths confusing your meter.

And to be sure, there are four 22 ohm resistors, R110,111,116,117, all in a group, right next to the Resonance control. Make sure none of them have gone open.

"After I put it back in the box..." OK, whatever you were trying to fix, did those tubes USED to light up before you tore into it? if that was always the problem, well we ned to just keep after it. But if it is a NEW problem that just appeared, then you broke a connection. Not saying you did something wrong, I certainly have done it. But flexing the boards and connections can break them.

The +/-25/23v supplies start on the power supply board, then move through a ribbon cable to the controls board. Down the length of that then cross over to the center board through some bare wire jumpers, then from there to the preamp tube socket board by way of MORE bare wire jumpers. One of those could have easily broken away from the board.