I think what he means by sync leakage is bias signal leaking through when overdubbing. There are bias traps for the record and sync/play tracks.
I don't know where the muting relays would be on an 80
Transistors..Yes! The early Japanese kit used really cheap, low hfe devices for muting and they used to fail, often going 1/2 off 1/2 on and noisy.
Replace with BC184L/214L depending upon polarity. There could also be high value base feed Rs, >470k and these can go high/O/C.
Dave.
I'd be surprised if the 80-8 didn't have relays in the signal path. I know the 38 does, and that was the second-generation deck. There was also some rumour that the lead designer quit and went over to Fostex because he wanted to start using solid-state switching in the audio path and TEAC insisted on staying with relays for some reason.
That can happen on a badly bulk erased tape. Run the tape in wind and listen to the output. If you hear a wopwopwop sound then its badly bulk erased. If you then recorded all the way through, thus cleanly erasing it, the effect will be gone. Effectively a very low frequency mag field gets recorded on the tape, and when you punch in on this you abruptly drop the level at the punch in point. Hence a click.??? By recording a blank signal through the whole tape and going back and testing again....no bumps on punch in or out....strange... Anyone ever hear of that?