Tascam 38- Capstan Motor issues

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Doompreacher

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Evening Everyone!
I’ve seen a number of Capstan Motor issues on this forum but I figured I’d ask regarding the issue I’m having...

With all this downtime, perfect opportunity to transfer those 1/2” tapes into ProTools! My Tascam 38 was in storage for a number of years. I recently cleaned the heads, demagnetized, and getting playback as well as rewind and fast forward are working. Tape path is clean and free of any issue. I decided to adjust the reel table height since I was getting uneven winds. I powered off the machine, adjusted the tables and put everything back together. I powered on, and noticed I didn’t hear the capstan motor spinning. Belt is intact, lifted the pinch rollers and still nothing. Pretty sure the capstan motor spins all the time on these. So I have a second “parts” Tascam 38. I pulled the capstan motor off that one, installed... And still no spinning motor.

Am I missing something? I know these machines are old and the capstan motors can be problematic. But two non-working motors? Everything else I should try? Any assistance would be greatly appreciated. Thanks!
 
That's correct. When the tension arms are lifted, I am able to rewind and fast forward... But not Play. The capstan motor does not turn.

However, I did replace one of the tension arms that was badly bent. I replaced the two springs that were connected to the tension arm and all is well. Is it possible I disconnected something that engages the capstan motor? Like I said, just seems unlikely I have two bad capstan motors.
 
Nope. Microswitch is intact and appears to be functional. When the tension arm comes away from the microswitch, and I press Play... The pinch roller engages and moves to the capstan. Just the capstan motor does not spin.

Is there any way to test the capstan motor directly? I could sworn I read that I could apply a 9 volt battery to the red and white leads to see if the motor spins?
 
Silly question, have you checked the fuse board? I forget how the 30-series work, but there might be a separate fuse specifically for the capstan motor.

EDIT: Yeah - if I'm reading the '32 schematics correctly, the capstan runs off a different fuse from the reel motors. I think it's F505 for the captstan and F502 for the reel motors...
 
Not a silly question at all. I did check the fuse PCB and everything looked pretty good to me. I think the 38 is similar enough to the 32. I take another look. I got to get a better copy of the 38 manual. The schematics are tough to read.
 

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Doompreacher said:
Not a silly question at all. I did check the fuse PCB and everything looked pretty good to me. I think the 38 is similar enough to the 32. I take another look. I got to get a better copy of the 38 manual. The schematics are tough to read.
Click to expand...

Did you visually inspect them or use a multimeter to actually test them?
 
Good call jpmorris. Breaking out the multimeter and testing the fuses.

Any advice on whether I could test the capstan motor? Were I able to apply voltage outside the machine and neither of the two capstan motors I have work... Then I simply get another capstan motor.
 
Doompreacher said:
Good call jpmorris. Breaking out the multimeter and testing the fuses.

Any advice on whether I could test the capstan motor? Were I able to apply voltage outside the machine and neither of the two capstan motors I have work... Then I simply get another capstan motor.
Click to expand...

If it were me I'd be trying to find out whether the correct voltage is getting into the motor, but I'm not sure offhand how best to do that. IIRC they're 24V DC motors usually run in a 12V configuration with an initial pulse of 24V to start them. So yes, if you know the pinout you might be able to run them outside the machine from an external power source.

EDIT: Which makes me wonder if the power transistors might be out to lunch. I find it a little hard to believe that both motors might be dead.
 
I’m right there with you. Just odd that’s it’s two capstan motors not working.

FYI: got all the fuses on the MM and they are all good.

Not sure about the right pin out and using an external power supply. I’m still a bit of a novice but if I’m pointed in the right direction... I see to do ok.

Any direction on what/where I should check on the power transistors?

And thanks for all the help jp!
 
Doompreacher said:
I’m right there with you. Just odd that’s it’s two capstan motors not working.
Not sure about the right pin out and using an external power supply. I’m still a bit of a novice but if I’m pointed in the right direction... I see to do ok.
Any direction on what/where I should check on the power transistors?
And thanks for all the help jp!
Click to expand...

Well, conveniently the service manual says stuff-all about how the capstan motor is driven. AFAIK they have a driver board on or nearby the motor itself which isn't documented.
However, if I'm reading the pinouts for that daughterboard correctly, pin 1 is either connected to 2 or 4 depending on whether it's high or low speed.I don't know what happens if neither is connected so if the speed switch has gone bad it might behave strangely. That might be worth checking if possible.
Pins 6 and 10 come off the PSU - it might be that one is a 24v line and another is 12v, but I honestly have no idea. Pin 8 is ground.
Pins 3 and 5 go to the varispeed control.

So, if those are connected to the motor assembly via a connector, it might be worth checking the voltages on pins 6 and 10 using 8 as your ground reference. Noting that they will probably only go live when the tension arm is activated.

The PSU section driving the capstan looks like it's on a daughterboard. That being the case, pin 1 is the power line from the PSU proper, pin 5 is ground, pin 2 goes to pin 10 on the capstan board, pin 4 goes to pin 6 on the capstan board, and pin 3 looks to be the input switching the capstan power on and off.
 
Thanks jp! I'm gonna give it a shot and keep you posted.

As a side note, I took both capstan motors and tried them in the "parts deck" Tascam 38 that I have. Neither worked there. So maybe I do have two bad capstan motors? But I think testing out the voltage on the boards is the only way to be sure.
 
So I tested out at pins 10 and 6 with 8 as the ground and I'm getting 32 volts. I also tested the actual solder points on the board leading to the capstan motor and also got 32 volts. Fair to say my capstan motor is no good?

Capstan Points.JPGPins 8 and 10.jpg
 
That worries me given that these are 24v motors. I think you'll need someone with more electronics skills than me to determine whether that's right, and if not, why it's doing that.
It's possible 32V is normal and the servo board is doing something clever to limit the voltage going into the motor. If not, it may be that this has cooked both motors - hopefully one of the components on the servo board popped before the motor windings.

EDIT: though reading it again it looks like you're getting 32V into the motor itself. That can't be right. I would definitely try and ensure that the voltage is 12v or 24v before replacing the capstan motor again, since the deck may well be killing them.
 
Hey Jp.... I did a bit of digging. The capstan motor is suppose to see 35v and it is regulated down to 24v by the servo PCB that the capstan motor is soldered to. I found an archived thread in which unsoldering the motor and testing the coaxial points (red/white) on the motor should be at 35 ohms. One of my motors is very dead at 0 ohms, and won't even spin freely. The other is at 13 ohms which appears to be dead as well. So I'm off to order a "new" capstan motor. Really appreciate the assist!
 
Good luck. It had occurred to me that it might be worth checking the resistance of the motor, or at least the continuity, but I didn't actually know what results to expect.
 
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