Help needed with Phonic PWA2200 Power Amplifier

[yush]

Hi, I have a Phonic PWA2200 power amplifier which needs repairs. Unfortunately there are no qualified technicians in my locality so i'm trying to repair it myself with the little electronics knowledge I have... So i really need help in fixing it.

So here's the problem:
When the amp is turned on with the speaker connected to the left channel, the amp outputs a dc voltage and immediately goes into protection mode. It keeps on doing that until the amp is turned off. The right channel does not give any output whatsoever.

Where should I start ?

 

[turk 182]

what sort of test equipment do you have?

 

[JMFahey]

With due respect, if no qualified Techs in your area, you won´t become one just by asking a few questions in a Forum.

You don´t even have the schematic

 

[yush]

what sort of test equipment do you have?

I only have a multimeter

With due respect, if no qualified Techs in your area, you won´t become one just by asking a few questions in a Forum.

You don´t even have the schematic

I don't want to become a technician... i just want help from one or someone who has the ability to fix one.
I tried to find the schematic but to no avail.

 

[stled]

Here is someone who has some other model schematics Free diagrams, schematics, service manuals beginning with P :: Schematics Unlimited

Many if not most of the designs should be similar

Here is a list of some manuals and also the company website
Box
Phonic | Manufacturing Quality Professional Audio Equipment since 1977

stled

 

[MAAC0]

So, You have DC. Have You measured the DC voltage before the protection relay or the output drivers already ?

 

[yush]

So, You have DC. Have You measured the DC voltage before the protection relay or the output drivers already ?

Yes I did, there's about 20v before the protection relay.

Here is someone who has some other model schematics

Free diagrams, schematics, service manuals beginning with P :: Schematics Unlimited
Many if not most of the designs should be similar
stled

Thanks a lot.

 

[steveu]

When amplifiers fail, it's usually the power transistors that fail first, which then destroys the driver transistors and bias circuit. If you replace the only the failed output transistors, the damaged driver and bias circuits will destroy the new parts as soon as you apply power. It is common to use a variac to bring up the power gradually while observing the results. Even if you get the amplifier working, you may overlook damage that does not affect normal operation. Repairing amplifiers is not something you can do with trial and error. You have to completely understand the design and test every part.

 

[JMFahey]

Agree and add: if it were a simpler amplifier, say one with LM3886 or some STK module, repair by a non Tech might still be feasible with "paint by the numbers" instructions, replacing the chip amp replaces in a single stroke power transistors, drivers, gain stage, input differential pair: all the semiconductor backbone with none left behind, very high probability of success; but this amp is a beast, quad rail Class H (or G , same thing) , not easy at all even for an experienced Tech with all the data available and a full workbench.