JVC VN700 power off problem

[starks]

Hi All,

I have a JVC VN700 which switches off after 12 mins or so of use. On re powering, it trips againg after a few seconds. Sounds like a component faliure but could do with some advice to save lenghthy check.

If anyone has experienced this problem or has any advice, I would be very grateful.

I have checked the amp without speakers and with one chanel only, same problem so I guess the output trans are ok?

 

[jaycee]

On an amp this old, it is probably the effect of dried out electrolytic capacitors. Measure the DC voltage on the speaker terminals from cold, and you will probably find it is rising slowly to the point where some protect circuit trips.

 

[jaycee]

Service manual here: JVC VN-700 | Owners Manual, Service Manual, Schematics, Free Download | HiFi Engine

 

[starks]

Hi,

Thanks for the advice, very much appreciated as I don't have an electronics background just some basic knowledge through messing around with vintage valve amps.

DC voltage measured over 100mv on one chanel so I took out one of the what I think are the preamp boards (TAD809) to test and found the culprit. The other board measures around 38 in both left and right slots.

With my limited knowledge, I will start by changing the caps and move on to resistors. I will have to do some reading on transistors!

Thanks again for your help