Nagra T - Tape tension stability issue.

[Rene]

Hello all,
My Nagra T is starting to show an instability in the tape tension system.
There is a mechanical oscillation that takes place around the tension sensor. It's audible when tape is rolling, and also affects the signal at the output.
It doesn't happen with all kind of tapes, but with some old ones I'm currently working on digitalization (could be some Scotch/3M, but I'm not 100% sure) ...
I'm looking for a Service Manual of this machine.
I'll appreciate any advice regarding this problem.
Many thanks.
Ren?.

[docb]

Probably a loose clutch on one of the capstan motors -

http://www.tapeproject.com/smf/index.php/topic,2005.15.html

[Rene]

Hi Dan.
Thank you for your answer.
I red carefully this topic 2005.15, I'm not sure to face the same problem.
My machine mostly work correctly, but a particular type of tape seems to trigger the issue.
It looks like a friction problem of the tape oxide onto the tension sensor.
This friction creates an audible noise, and induces a kind of modulation also on the output signal.
I would like to check if this oscillation exist electrically on the tension control loop, and have a general check on test points in this area.
For some reasons it could be that this loop is a bit susceptible, and this friction could be enough to push the tension regulation to oscillate.
It's always difficult in a close loop system to discover the root cause.
That's why I'm searching for the Service Manual.
Thanks again for your time.
Ren?.