JVC AX-Z1010TN amp problem - help please

[Nick_G]

Hi all.

I've had this amp since 2015, after @flatpopely reviewed on here. It's given sterling service, and sounds fantastic.

However, tonight, something is not right. The audio output seems diminished, there's signs of distortion, and if I crank the volume knob up halfway, it goes into protection mode and cuts out.

Help! Is this likely to be something terminal?

Thanks.

 

[Gerard124]

If your anywhere near Nelson in Lancashire there is a HiFi shop called Wilkinson's HiFi. They do repairs and their website mentions they are JVC enthusiasts with a JVC museum - might be worth a phone call?

 

[Nick_G]

Thanks Gerard. I'm actually in north Hampshire, so nowhere near Lancashire. However, I realised I still have Henry, 'toprepairman's email address so I have also sent him an email as he serviced the amp when I bought it in 2015. Any ideas about what may be wrong would be much appreciated.

 

[flatpopely]

Check for issues with the speaker wires. A stray one many be shorting out.

Unplug every cable and see if the problem goes away.

 

[Nick_G]

Check for issues with the speaker wires. A stray one many be shorting out.

Unplug every cable and see if the problem goes away.

Thanks.

I just tried disconnecting the speaker cable from the speakers and then reconnecting them, but the problem remains. I think further investigation will have to wait.

 

[Tony L]

Have you got a multimeter? If so the first thing I’d do is to check for DC offset at the speaker terminals with volume at zero and the speakers disconnected. That will give some indication if things are very wrong and if there is a risk of damaging your speakers. You are looking for <50 mV or so.

 

[Nick_G]

Have you got a multimeter? If so the first thing I’d do is to check for DC offset at the speaker terminals with volume at zero and the speakers disconnected. That will give some indication if things are very wrong and if there is a risk of damaging your speakers. You are looking for <50 mV or so.

Thanks. I don't have a multimeter but my father-in-law may have one.

BTW the problem occurs if I'm using headphones as well, which bypasses the speakers.

 

[flatpopely]

Thanks.

I just tried disconnecting the speaker cable from the speakers and then reconnecting them, but the problem remains. I think further investigation will have to wait.

You need to disconnect everything and try again.

 

[Dave49]

I have a Revox A77 (circa 1973) which no longer runs at playing speed; anyone know someone in Surrey area who might specialise in such repairs.

 

[Zombie]

I have a Revox A77 (circa 1973) which no longer runs at playing speed; anyone know someone in Surrey area who might specialise in such repairs.

You would increase the chance of finding such a person with your own thread on the subject instead of burying it somewhere irrelevant.

 

[Dave49]

You would increase the chance of finding such a person with your own thread on the subject instead of burying it somewhere irrelevant.

Thanks, I’ll do that.

 

[Nick_G]

Well, I've just sent the amp to @toprepairman (Henry) to be examined and hopefully fixed. It seems that there may be a problem with the preamp stage, as when the volume is turned up quickly the trace on the oscilloscope wanders about badly. Somehow DC output is getting through in both channels, and this is what is causing the amp to go into protection mode.

Now to find a service manual/circuit diagram...

 

[Nick_G]

Try this service manual that I've uploaded to my Google Drive account. Operating manual shows first then scroll down to get service one.

https://drive.google.com/file/d/1mBYtH0hiyWrukkJ3Gub0QiOmvO9ZvKAZ/view?usp=drivesdk

Thanks. I found one on Elektrotanya and have emailed it to Henry.

 

[mikeyb]

Thanks. I found one on Elektrotanya and have emailed it to Henry.

Cool