Peavey CS-800 no power

[The Dude]

IMO, that means the transformer is most likely good. Here's some documentation on the power switch including switch schematic. One side of the rocker switch (if that's what you have) is for the internal neon indicator lamp.

https://peavey.com/manuals/80300037.pdf

With switch on, I'd check to see that AC is getting to the transformer primary measured right at primary leads.

[nosaj]

Any chance you have the diagram for the transformer wiring for the cs-800s?
nosaj

[The Dude]

The transformer wiring is in that .pdf in post #31.

[Axtman]

What is the purpose of the triac in the power circuit? Thanks.

[nosaj]

What is the purpose of the triac in the power circuit? Thanks.

To reduce the voltage/current the switch sees I believe.
nosaj

[nosaj]

The transformer wiring is in that .pdf in post #31.

I knew that :facepalm:
nosaj

[Axtman]

After thinking about my question, I thought maybe the triac acted as some sort of relay. I thought maybe the amp had a teeny tiny micro button switch with hair thin wires going to it. That would make sense to have a triac. But then I looked up the amp and see that the power switch is a big hulking rocker switch.

[nosaj]

Either G1 or The Dude said they replaced lots of the rocker switches in the past so the triac may have been in response to that. These things are pretty stout and heavy thats for sure.
nosaj

[Helmholtz]

As g1 pointed out in post #2 the rocker switch just triggers the triac being the actual power switch.
Current through the rocker switch is low (mA).

But without the triac the switch would have to handle the huge turn-on surge currents of the PT which might approach 50A peak, often tripping the house circuit breaker.
Such high peak currents tend to quickly wear- out/scale mechanical contacts.

This would explain frequent switch failures with earlier versions and why PV added the triac.

[Helmholtz]

What still makes me wonder is the shorting triac at the output.
It's wired like a typical phase control dimmer having a long time constant, thus won't trigger with signal.
It does protect the speaker from excessice DCV (>33V) at the output.

But won't shorting the output cause even more damage to the amp?

[g1]

But won't shorting the output cause even more damage to the amp?

It's just very basic 'crowbar' protection circuit that is supposed to blow the fuse. I guess they are hopeful the fuse blows fast enough to save from further damage, but also placing a higher value on speakers than amplifier (and willing to make the sacrifice). These decisions would have been based on warranty costs I think. Most users would have been mating them with Peavey PA cabs.

[Helmholtz]

I guess "crowbar" means protection by brute force.
Does the triac always survive this torture given the huge short circuit current provided by filter caps?

[g1]

No, many times the triac fails because of the current. Sometimes it is the only thing that fails, other times output devices and associated parts also fail.

[Helmholtz]

I guess it always fails shorted, so still protects the speaker?

[g1]

Yes. Like putting a crowbar across the output terminals.