JVC HR-S6700U Hi-Fi issues.
 

Hello there. I bought a JVC HR-S6700U S-VHS unit 5 months ago and it has the following problem with the Hi-Fi audio:

When I play a monaural tape, the machine plays it well, but when I try to play a stereo tape, this unit only plays it the mono track, ignores the Hi-Fi track and the "Hi-Fi" mode turns off when that kind of tape is being played. The ironic thing is when I press stop, the "Hi-Fi" light turns on again.

I have cleaned the video head drum, but it hasn't solved the Hi - Fi trouble.

Have you tried to record with the VCR itself and see if it playback the Hi-Fi track, recorded by itself, correctly?

There are very small, surface mount capacitors on a circuit board which is raised up on the audio board.
They go bad. They are a pita to change but I'm working on mine now. They are 10uf 16v.
If you are good with electronics, it is repairable.