EDIT : cant get your email address to work so posted here..
really very good of you to respond,
well, the machine looks in very good condition, all works, records, plays and all sounds good, BUT,
There is a level fluctuation simultaneously every once and a while , for example,
with no tape loaded, using the on board Oscillator, monitoring the input, every now and again, the level jumps 2.5dB up then back down, some times it stays up, but mostly it jumps up and down, once every 5 minutes approx.
with a test (tone) tape loaded, it does the same thing but only jumps 1.5dB, again not very often but its definitely happening.
i have checked all the wiring on the back plane, re-seated all the cards but nothing i can do can make it happen, it just seems to happen on its own accord.
at first i thought it was a bias issue but its happening on the inputs with no tape loaded so now i'm confused a little, thinking it could be component problem, but remember it happens to both channels at once so it has to be common to both,
I look fwd to your reply,
all the best
Pete