Zeck PTV2200 September 2022 update!
This one lead me on a merry dance and three quarters. May save you time.
Came in several years ago for all the usual faulty bits to repair. They are not too bad to work on. This time, the report was that it in Protection mode. Bugger I thought. Another load of power transistors and MOSFETs to fit. Popped it on the bench and gave her some I2R via the power limiter and came on as normal. Umm. No DC at the output section before the speaker relays. Connected up dummy loads and an input to each channel via the jacks. 500 watts a channel, no problems. Left her to get all hot and sweaty for half an hour, all fine.
Called the customer who said that it went into protection as soon as he connected the XLRs from an active crossover unit, which was in the carry case. Okay. Set it all up on the bench and as soon as either XLR plug was fitted, the speaker relays operated and the protection LEDs lit? Switched off the active crossover, same thing. Removed the mains plug from the crossover and all was okay? So, have we got something odd going on with earths? I then noticed that the Earth Lift switch on the rear was set to lift. As soon as I set it to Ground, the Protection cct was activated. Scoping around showed that with the earth lifted, there was a 5V DC offset with ripple between the ground pins of the XLRs and chassis. Not having a diagram for this, I had to activate brain, which really is annoying these days.
Long story short, it would seem that the preamp input stages are fed from isolated sections of the mains transformer, having their own PSU sections. Scoping around the various supply lines and +,- volt regulators, there was a lot of ripple with unequal plus and minus lines. This obviously upset a virtual earth configuration at the front end, causing the protection circuit to have a hissy fit. With a handful of capacitors replaced and a couple of dry joints repaired, we now had equal +,- supply lines and no silly imbalance on the floating grounds. All was okay.
Another Zeck amplifier sorted. Slightly smaller than the last one done the other week, this being A PTV2200. Still powerful and capable of waking you up in the morning. Good design and you can work on when in pieces, which makes life much easier. Getting a few of these in with problems within the protection circuit. Which, seems to work well as I don’t see these with blown up output stages. That’s great considering these poor things have to tolerate mindless reggaeton being pumped through them at full tilt. Now I offer a basic charge for full refurb, covering all parts causing known faults. New capacitors in the power supplies and other checks to make sure reliable operation.