Studer A807 help

F

fgonza2

New member
Just got my studer A807. It works but it has a problem. AS i was doing a full check up i saw something strange on the brakes, so i calibrated the brakes, and i found that the left motor is always running, even with no tape installed on the machine. By simply powering on the machine, the left motor starts running, very strange. The brake was over tightened so it was static, play, ff, rw and all other functions work so far. I have the service manual which is huge, going through it right now. Does this behavior rings a bell on anyone with experience on these machines ?

thanks
 
thanks for the info. As i have two machines, i swapped the ROM chips. THe one with the issue is 20/92 version, i swapped it for a 20/91 from the other machine, behavior is the same. I think it is related to a sensor as the transport thinks there is tape. I tried cleaning the sensors but the behavior remains the same. I'll continue troubleshooting, to see if i find anything new on the meantime thx
 
I'm happy, i found the problem :) I traced the spool motor control signal and found a bad OP-AMP (NE-5532). There was no output change even when the input was changing. IC11 on the transport control board, Replaced it and voila. It's working now. How did that happen ? good question, but i found that probably a crappy technician worked on this machine inside at some point in the past, and the solution that was implemented to this "problem" was to tighten the brakes so the motor was stopped, which was really stupid as it held the motor static when power was present, glad the motor wasn't burned by this. hopefully this may help someone in the future if they hit a similar problem.

Studer M1 control.png
 
the celebration didn't last long... :(

I continued to adjust the machine and i found that the tension pots have no effect. So basically the back tension control doesn't work, i will check now the rest of the circuit as likely there are other issues with the control circuit. So i'll keep working on it, hopefully someone chimes in to enlighten me :)
 
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