Someone gave me this nice condition Sony BM-17 to have a go at fixing. Thought it might be just a belt change, but things are never that straight-forward, are they? This is a ‘Business Machine’ (BM) dictation device that takes a full size cassette. The sound is mono, but it uses an additional track to record a tone to help locate beginning and end of material - a bit like chapter markers. I can’t find a service manual for this, but the mechanism seems very similar to the much more common TCM-2. I ordered TCM-2 replacement belts for this one. The machine powers on (led light comes on at play) but the reels do not turn. I opened it up and sure enough the belt had turned to goo and was badly wound around the motor shaft. I got it cleaned up, but putting batteries back in, still no movement from the motor. I thought perhaps the motor was fried, so took the unit apart further and was able to test it: 1.5v direct to the motor, and it is actually working fine. So something is preventing power getting through to the motor and I guess I have to pull out the multimeter and start checking the components on the board. Any thoughts on the likely problem, or where I should start looking? I did not notice any loose or broken wires when I first opened the unit. Thank you for any input or suggestions!
My guess is the unit has been powered with reverse polarity at some point in time. The motor governor IC (AN6612) always burns when powered with reverse polarity. Check to see if you have the reference voltage (about 1.2-1.3V) at pin 2. If not, you can proceed in replacing the IC.
That's a great suggestion, thanks so much Valentin! Pretty amazing that those ICs are still available new today. I will try and confirm this is the issue this weekend. Will update in due course.
