A typical fault on these old Fostex M80 recorders is that the LED bar graph VU meters fail. These are 8 separate circuit boards.
The plastic "light guide" can be removed, which reveals chip LEDs bonded straight to the circuit board. The bonding wires tend to fail on these.
I scraped off the LED chips and replaced them with 0603 SMD LEDs.
The new LEDs are much brighter than the old ones (see the two rightmost modules in the picture below), so I replaced all 96 of them although only a couple were broken.
The next thing to fix was a Rifa capacitor. These tend to failover time. This one was not broken yet but I replaced it anyway.
The recording head was worn. Channel 1 even did not record properly, although playback was OK. I determined that the work groove on the recording head made a small air gap between the tape and the head so that the magnetization was not strong enough. Relapping recording heads can be done by professionals at least in the USA. But I was in a hurry and did not want to pay too much, so I did it myself.
The pin that lifts the tape from the heads when fast forwarding or rewinding was also worn. I smoothed that one out also.
