Tascam 34b Capstan Motor Problems

B

Barry P

New member
Hi all,
I’m New to this forum but hoping some of you may be able to help. I have just acquired a Tascam 34b, it did have a problem with the capstan, the drive belt was stuck jamming the motor pulley. I have stripped it down and cleaned the remains of the belt off. Unfortunately the motor didn’t run. I was expecting more problems I stripped the motor and found the internal inductor was blown. I have replaced the inductor but the motor still didn’t run.
The reel motors run fine and the tension arm switch work as it should, it’s just the capstan doesn’t operate.
I have un soldered the motor from the PCB and tested the motor with a small 12 volt battery and the motor runs fine.
I am now thinking it is the PCB or the drive transistor, so I unsolder the main D880 transistor but that seems fine when tested. I have checked all of the fuses, all good.
Any thoughts or ideas will greatly appreciate.
 
Hi there. Nice job so far with what you’ve tried. I think if it was me I would start with making sure the capstan servo board is getting power, and then maybe with the motor disconnected doing some load testing...so, strapping various value resistors across the + and - outputs of the servo board and measuring the voltage drop both at the +24V input and the servo board output. My thinking here is that if you get significant voltage drop at the output with a relatively small load, there is still something wrong with the servo board. If you get significant voltage drop at the input of the servo board, then likely there is a problem with the power supply or a fault somewhere in between the servo board and the power supply. The point is to try and isolate or narrow down where the problem is. DC servo amps are not an area of knowledge for me, so if your problem is on the board I’m sorry to say I can’t be of much help. Maybe others who know more in this area will chime in if you identify that’s where the problem seems to be.

hope that helps.
 
Another thought...so the motor runs with that 12V battery supply...what happens if you power it from a known good 24V supply?

and another question: when you have the motor powered from a known good supply, how easy is it to stop the motor? It should be difficult to stop it with your fingers...like, maybe you can’t even do it. If you are able to stop it relatively easy with your fingers then maybe the motor overheated and insulation on the windings is compromised and there is power shunting in the windings...the motor can still physically spin and be powered and run, but it’s compromised.
 
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