Peavey Mark Viii AC Wiring question

[patrick007]

Hey guys I am working on a Mark Viii Bass head that was opened by another individual. I am having no issues going through the 602 module but the schematics I have don't seem to be showing me where the two long yellow wires, wrapped in clear plastic sleeve coming off of the chassis mounted triac and main fuse holder are supposed to go. When I received the amp they were both plugged into TB1. This arrangement promptly blows the mains fuse. I am guessing this is not the required wiring as TB1 is normally closed. Any help sorting this out will be greatly appreciated! Whoever offers a solution I will paypal you a pint

[Jazz P Bass]

Here is the schematic & board layout.

[patrick007]

Here is the schematic & board layout.

Thank you for posting those schematics, unfortunately they do not show the mains wiring, or im stupid and missing it. much appreciated though

[Enzo]

Think you have a revision difference.


There is one TB NO 60 degrees, I think the one with the blue wires. TB = thermal breaker. That is the fan speed. It closes when the heat sink hits 60 degrees, and shorts across the 400 ohm fan slowing resistor, thus bringing the fan up to full speed.

The other one is NC 100 degrees. That kills power to the amp by opening if the heat sink gets up to 100 degrees. On this amp there is a large triac the power switch controls to turn the amp off and on. I believe the yellow wires place that breaker in series with the incoming mains between the triac and the next part.

Your pictures are a bit too close to see the whole wiring scheme from here.

[Enzo]

The mains wiring is on the schematic, the thermal breaker is not, that is what I mean by a revision. As production moves along on any product, then make changes to it, and those changes are not always on the drawings until their next revision. You are not stupid, the breaker in question is not on the schematic. If i were looking at it, it would be simple, but describing is harder.


And you might contact customer service at Peavey and ask for the AC Mains wiring diagram for the model.

[patrick007]

Thanks guys for the replies! I think I figured out the mains wiring. I emailed peavey but haven't heard back as of yet, roger referred me to the guys in repair for the mains wiring. It is no longer blowing the mains fuse with the main filter caps removed. I don't have a cap tester that goes to 10k uf but one of the caps was getting quite hot. No biggie, on to the 602 module again, thanks for the help, if I have any more questions I will post them here.

[patrick007]

well im stumped again. my low voltage section isnt blowing fuses, but something is clamping, the xfrmr makes an inductive bumm when im guessing the boardmounted traiac opens. i am suspecting the bidirectional trigger diode but im stumped. any ideas guys?

[Enzo]

what exactly are we fixing now? You have the orange wires and the red wires from th transformer to the board. Unplug them. Now all we have is the primary wiring to the transformer. Power it up. Measure AC voltage at those wires. I expect to see something like 100vAC center tapped between the red wires, and maybe 30vAC or so center tapped on the orange wires. If you get that, then the whole transformer/triac/etc part is working. And move on.


And you know what? If you still have yellow wire mysteries, just wire the thing up like the schematic says, and move the wires aside somewhere. Get the amp working and we can worry about yellow wires later.


DO NOT connect a speaker or load to the amp until we are sure it is stable.


With nothing plugged into the speaker out jacks, measure resistance across the speaker jack. Is it shorted?

You have a couple rows of output transistors, and any of them shorted?