Peavey PV 8.5C DDT is activated on channel A even al low volume, channel B works fine. All 8 power transistors on both channels were found OK. Driver transistors and 15V zener diodes are all OK as well. Supply voltage on both channels are all OK. Triac and switching transistors on the PA board were found OK. Any help is highly appreciated. Many thanks. Leo

Suggest you take your amp to a Peavey dealer for a diagnostic report

check output transistors also the driver transistors.

DDT circuitry malfunction.

Suspect that the pot is broken, or start cleaning all the back switches, this pv amps suffer from a terrible switch quality.

Here is a link to the manual:http://www.peavey.com/assets/literature/manuals/00512180.pdf Page8 sections 2 through 4 discusses the LEDs. I think what you arte talking about is the DDT active LEDs. Page 12 specifically discusses this and page 15 notes that Red signifies DDT clipping. Peavey recommends that you don't defeat the DDT circuit and that is good advice as it protects your amp and your speakers. The clipping is not caused by the amp but by the amount and quality of signal being input. Check earlier in your signal chain for the cause.

Disconnect the speaker wiring and speaker on the bad channel. Turn the level control(s) all the way counterclockwise and turn the amp on. If your DDT (limiting) light remains lit, it's time for a visit to your nearest certified Peavey service center....G.

Chances are you have NOT got all the bad parts out yet.

HINT: While cold starting an amp after it smoked, put a 150 wat lamp in series with the power cord to act as a current limiter... saves fuses and parts.

The DDT circuits PROBABLY look for amplifier DC balance AND no overload of power supply as protection.

They COMPRESS the audio when it goes above a certain level.

SO, to troubleshoot this you will probably need an oscilloscope.

LOOK for a supersonic oscillation that you cannot hear but MAY be driving the amps beyond the DDT trip point. Drive a pure low level sine wave into the amp and follow it through to see at what point the DDT compressor senses an out of range level.

Remember it HAS worked before, and there is still a bad part in the unit. DO use my suggestion to limit the current as often while troubleshooting this type problem, the signal will suddenly go to a point to fry something, then you get to replace all the parts AGAIN.

The unit is only partially smoked. There is a problem in the final output stage, not enough to shut it down completely, but close. The DDT light indicates that the amp is outputing full power. I suspect that there is a partial short that is presenting itself as a low impedence load to the output amp section. This is causing the amp to work really hard and thus the DDT light kicking in. I think you will find 1 transistor shorted or partially so. Replace ALL of the output transistors for that side and that should resolve the problem. Check the driver transistor pair as well. It is important to replace all of the transistors on that side, even if some check OK with a checker.

Dan

Go to http://peavey.com/support/searchmanuals/archived.cfm Their main site also has info. DDT is an active compression feature to protect the product .

the ddt circuit on this amp is goofy, they use a 4060 opamp with the inputs at -14 to -15V, the spec range is only +/-12V. So it is possible for it to nuisance trip. There is a button on the back to disable the ddt, try that. I've alos had luck replaceing the 4060 with an LM358 whose input spec is not violated in this application