Audio problem with old 1984 JVC GR-C1

tuvieja

Hi.
I purchased, not too long ago, an old JVC GR-C1 (the famous Marty McFly camera). When it arrived, I tested it, and it was working great. I made a couple of recordings, and everything was fine. The battery was dead, but the camera came with an original JVC wall plug adapter, and, as I said, was working and recording great.

A couple of weeks ago, I had an 80s party at my house, and I wanted to record some videos with it.
When I checked the videos, there was no sound. I have the AV output cable, so I connected it to the TV, and my old recordings had sound, but these new recordings from the party had no sound at all.
I also tested not recording into a tape, but just putting the camera in record mode, so I can see the picture and hear the audio in real time from the TV thanks to the AV cable, and no audio can be heard.

A friend of mine has the same camera. I tried his microphone with my camera, and I have no sound. If I connect my microphone in his camera, it works. So the problem is not the microphone.

As I'm kind of good in electronics, I disassembled the camera so to get to the audio board, to check if there was any blown fuse or capacitor. I can't see anything strange on the board. There are no fuses, but the capacitors look ok to me, they're not fat or blown.

Anyone had a similar problem? Any solution?
Thanks a lot!