Help with Otari 5050 MK III 8-track back tension adjustment

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kilmister

Well-known member
Joined
Aug 22, 2008
Messages
284
Location
Helsinki, Finland
Hello all!

I have Otari 5050 MK III half inch 8-tracker on my bench.
Machine runs smoothly and feels to be in pretty good shape but when I fast forward tape and then rewind it tachometer leaks many many seconds.
I've found some writings around net which tells too weak back tension in reels can cause this kinda problem.
Found also service manual and schemas but couldn't find anything about back tension or how to adjust it nor how much torque there should be.

All help is very much appreciated,
Paavo
 
Are you sure its back tension that's the problem, or the tacho assembly incorrectly adjusted?
These things usually use two photo-interrupters and a slotted wheel to generate two square waves at 90 degrees out of phase. If you have overlap in this then it will not generate correct pulses for the counter.
Connect a dual trace scope to the two outputs, and check that they don't overlap wrong.
 
Thanks for tip radardoug.
I checked that but square waves are nicely 90 degrees out of phase in all play, FF and RW modes.
What I forgat to mention is leaking happens when I FF reel almost at the end and back then. If I FF only to 5 minutes or so and rewind it does not leak so badly. This forwarded me to assume it's about back tension.
 
I have this exact same machine.

Do you have a calibration procedure for it?

I need one, I'm having a hard time with calibration.......
 
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