Mellotronists

Hello to you all,

I'm new to this group, I bought an EMI -made M400 about 2 months ago.
It needs some work, maybe some of you would be kind enough to lend me
a hand? I am quite familiar with electronics; I've made two guitar
tube amps + effects myself. I've already fiddled with this mellotron a
bit: I've changed the electrolytics of the PS, I've tried to clean the
tape heads, etc. Let me describe what's not right with our M400 (I
bought it with a couple of my friends):

1. It has a terrible earth loop, appearently. When it is connected to
an amp, there is a loud hum, even when the mellotron is off (but
connected to the mains). When the power cord is disconnected, the hum
goes away. I reckon this is an earth loop, but how on earth should I
fix it?

2. The output seems weak, much less than an electric guitar. There is
a few things related to this, I think. Firstly, the tone pot wasn't
working well, so I tried to replace it - now it won't scratch anymore,
but it works like a volume pot, which I guess isn't normal. Secondly
the tape heads are covered with something, that alcohol didn't solve.
Can this affect the output? I think the heads haven't been cleaned
ever before the unit came to my hands.

3. The tape rack is from a normal M400. I realized it won't fit like
it should - when looking the mellotron from the player's view, it
makes contact with the mainframe(?) on the left. It forces the thing
to the left, so that even the tape-collect-box is moved (this is kind
of hard to describe...)

4. The last thing is related to the former, I think - the touch of the
keyboard was awfull, I changed it a bit and now it is much better -
but still, it should be a lot better. I can feel the tape "struggling"
under some of the keys while they are pressed.

Also, the middle C is much quieter than the other notes. Actually, you
can barely hear it - I am quite certain it is not the tape, but
perhaps the tape head that is at fault.


So there you have it. This is the second working mellotron in Finland
at this time, so we don't have too much info on the maintenance of
this instrument. Any information would be greatly appreciated!

Thanks,
Best regards,

Janne