I was attempting to do a health checkup on a friend's Nagra 4.2 and before I could even run an MRL tape to check response and azimuth I noticed that the tension was acting very strange.
The tension rollers for both the supply and take-up sides are bouncing up and down adding a horrible wow to playback. The motor mode on the meter shows the current wildly fluctuating in time with the rollers if that gives any clues. The issue seems to eventually go away while running at 15ips but persists at 7.5 and 3.75ips. The tape stock isn't sticky and the tape path is very clean. The machine had been in storage for at least five years though.
Just wondering if this is a familiar problem and if anyone has any ideas of the cause?
I'm still searching for a proper service manual but it would be great if I could get some clues in the interim.
Also, does anyone know if there's any easy way to determine the EQ curve of a 4.2? I own a Nagra IS-LT and a "NAB" sticker was attached to one of the PCBs.