Peavey 400BH temporarilly gives up

[Anjo]

My Peavey 400BH MARK III series is behaving strangely.
Sometimes, like 1 out of 10 playing sessions, it suddenly goes in to a state of very low volume and distorted sound. Turning it off and back on again (after 10 - 15 minutes rest) gets it back on track.
Any suggestions on what’s with my unreliable amp?

Thanks,
Anders

[Enzo]

Dirty patch jacks come to mind.

Ball up your fist and whack the top of the amp hard when it happens. Does that have any effect on the amp? Turn the reverb down first if it has one. If hitting the amp makes any difference, there is a loose connection inside - start inspecting the solder.

[Anjo]

Thanks for the tip. I’ll try that when it goes bad next time. I do believe I hit it in frustration several times before but maybe not systematically from different angles etc.
Many thanks
Anders

[Enzo]

It is not a precision method, it just makes loose connections show up.

Plug something in and out of the various patch jacks. If that helps or hurts, then the jacks need service.

[Anjo]

Well I guess I'll start checking the soldering any way. I've tried shifting between the jacks when the amp goes faulty without success.
Many thanks

[punkrock]

Peavey 400BH MARK III schematic?

Does anybody have a schematic for Peavey 400BH MARK III 1978?

[Enzo]

400BH is just the power amp on the rear panel. If that is all you need, great. The front panel should have the model name, such as Bass or Standard, or whatever.

And for future reference, you can get any Peavey schematics by just calling or writing customer service at Peavey.

[punkrock]

front panel

Thanks for the information.
I need the front panel too. the model is "Bass Mark III Series 1978". I hope that it is the right name of the amp.

[jbltwin1]

400 BH

Sorry, All I've got is the schem for the power amp and the front end for an xr600b mixer. The stuff IS the same other than values obviously. The mark lll has the front end loading values different but the ratio is still the same.

[jbltwin1]

400bh

OOPS-didn't see ENZO had nicely attached the schem. If it's intermittant, it's probably loosing voltage to one of the power transistor rails. I'd wiggle the connectors at the power board and make sure they're not loose FIRST. Those power sections are really pretty bullet proof and they only seem to eat output transistors so they get great service out of them.