Please Mr Charles Hansen and Konrad: help!

[Daneel]

Hello to all! This is a preliminary search for a solution in a strange issue involving a Swiss Physics model 6A power amp.
This amp has performed flawlessly till few weeks ago. One of the two channels now seems to switch in protection after 3 minutes from the powering on.
The strange thing is that during the first 3 minutes music comes from both channels as it should, then the left one flip in protection. Is anyone having troubles with the
output relay? Could be a load-related problem? The boards inside, at a first inspection, have no burning or melted, fused component. I'm trying to address the problem before looking for an expert technician. Any help will be greatly appreciated. Please would you receive my best wishes for a happy new year.

[maxpou]

You don't have schematic? It would be useful to help you. Maxpou

[Daneel]

Unfortunately I haven't any schematics. This was a particular amp, made by a little and very specialized company, I think that no schematics were ever published or released...

[Daneel]

I know for sure that Mr Hansen and Konrad, from this forum, are aware of my problem! I hope they read my request!

[Charles Hansen]

Originally posted by Daneel
Hello to all! This is a preliminary search for a solution in a strange issue involving a Swiss Physics model 6A power amp.
This amp has performed flawlessly till few weeks ago. One of the two channels now seems to switch in protection after 3 minutes from the powering on.
The strange thing is that during the first 3 minutes music comes from both channels as it should, then the left one flip in protection. Is anyone having troubles with the
output relay? Could be a load-related problem?

I am sorry, but I cannot offer any advice. I have never heard of Swiss Physics and know nothing of their design. I have never used a relay to the speakers as protection, either. The only protection "circuit" in my designs are the rail fuses to the output stage and a circuit to sense DC at the output.

The advice from Maxpou is very good. If you have a schematic, it will much easier to solve your problem. Good luck.

[Conrad Hoffman]

A thought from a different Conrad- Some protection circuits have a filter or detector consisting of a discrete transistor and capacitor. If the cap goes bad, or the transistor becomes slightly leaky, the circuit will malfunction. There could be a hundred different causes, but you need your expert technician for any of them. This probably isn't something you can fix without a schematic and without the right test equipment. Without seeing the circuit, it's impossible to even guess.

[QSerraTico_Tico]

Originally posted by Daneel
Hello to all! This is a preliminary search for a solution in a strange issue involving a Swiss Physics model 6A power amp.
This amp has performed flawlessly till few weeks ago. One of the two channels now seems to switch in protection after 3 minutes from the powering on.
The strange thing is that during the first 3 minutes music comes from both channels as it should, then the left one flip in protection. Is anyone having troubles with the
output relay? Could be a load-related problem? The boards inside, at a first inspection, have no burning or melted, fused component. I'm trying to address the problem before looking for an expert technician. Any help will be greatly appreciated. Please would you receive my best wishes for a happy new year.

Measure DC offset till the relay opens.
Also check DC-offset before the relay to see if the fault is in the relay circuit or the amplifier.

[Daneel]

Thanks to all the members for the support! I was very busy these days, sorry for my late answer.

- To Mr Hansen: I supposed you knew this amp, reading one of your old replies in the thread:"a substitute for Hitachi 2SJ55/2SK175 mosfets". I was wrong, please excuse me.

- All the other suggestions will be taken into account

My last hope is Konrad. I can't contact him directly via email, the server says that I haven't acquired the full membership status yet...

Daneel