TASCAM 34 capstan motor

[Adinol]

Greetings,

I am servicing a Tascam 34 that I managed to pick up for a great price.

The capstan motor does not spin when I engage the tension arm. I already did some troubleshooting but I want to make sure I don't mess anything up on my next step.

The motor connects to the control board with a pair of coax cables, one with red center and one with white center. On another forum someone advised me to desolder the connection to the control board and apply 12V DC to the red and white wires to see if the motor spins. But I am not clear on the polarity.

Which wire should be connected to + and which to - of the 12V DC?

I don't want to just try my best guess, as I don't know if reversed polarity can damage the motor.

Thanks...

 

[Michael Doncaster]

Red +, White -.

 

[Adinol]

Thank you for the info.

I desoldered those wires from the control board. First measured continuity/resistance between red and white wires. I do not measure any continuity nor resistance.

I hooked them up to a variable DC power supply and slowly increased the voltage to 16V DC. Motor does not move. I also hooked up through amp meter and there is no current.

It could be just a connection in the motor, right? At this point I feel I have nothing to lose if I open the motor and look inside. But before I do that I wish to ask if there are any unexpected surprises, if I open that motor. Any spring loaded stuff that can't be put back together?

Thanks...

 

[wkrbee]

If the motor doesn't spinup when you give the motor a spin when powered,you could have a broken/worn brush spring,

 

[Adinol]

I opened up the motor and discovered that I wasn't the first one there, because there was one plastic washer that was already out of place. On the stator side there is one component that looks like it used to be a resistor, which is burned out.

Does anyone knows the value of this resistor (ohms and watts)?



Thanks...

 

[SkywaveTDR]

The burned out part is an Inductor and I think they are marked as 10mH in other equipment and they are spec'd for more than 1 amp. If that burns out the motor could be compromised and the rotor part needs work. This need to have the commutator cleaned of carbon and then to make sure each pole reads the same resistance. I have worked on many motors but not all of them return from the dead. Some are simply burned up.

 

[Adinol]

Thank you for your reply, Skywave.

I am also maintaining a thread on the Audio Karma forum and member dhnash (who I believe is also a member here) pointed me to this old thread:

http://www.tapeheads.net/showthread.php?t=60058&highlight=inductor

I have made some progress, but have more work to do.

My motor is definitely burned and I need to determine if I want to try rebuilding it. So far I know this:

1 - the inductor is burned.
2 - the electrolytic cap leaked (I would replace it with a film cap on the outside)
3 - the rubber reinforcements on the brushes melted
4 - the 7-terminal soldering ring, to which all the coils are soldered to is damaged
5 - three of the coils have burned wires (like blown fuses)
6 - there might be shorts within some coils, as I measure lower resistance
7 - the D880 transistor, on the control board, is dead (short between C and E pins)
8 - the contacts of the brushes do not show much wear

I measure the magnet wire to be .14mm, so I guess it must be 35-AWG wire. There are 7 coils and I guess I can count the number of turns as I unwind and replicate that as I rewind.

At this point I wouldn't mind getting some advice from anyone that might have attempted this kind of repair. How likely am I to succeed? I am quite good with precision work, so I believe I can rewind a rotor, patiently. Also, once the coils are wound, do I need a strobe to balance the rotor.

 

[SkywaveTDR]

When the disc around the commutator is cracked apart and broken I do not proceed on that as the fields are also possibly damaged.
Put a BR20 motor onto the servo board and calibrate. That is the easy way.

 

[Adinol]

Thanks for the info.

For my better understanding, what do you mean when you say the fields are damaged? Do you mean the magnetic fields of the permanent magnets, because they also overheated?

Also, I do not get much Google info about a BR20 motor. Is a BR20 an upgraded version and thus a better option? I also don't know what the calibrating procedure would be, if I went that rout.

Since I have no past experience with this work, would it be a better option in my case to just get the exact same replacement motor?

Thanks...

 

[SkywaveTDR]

It would be great to get a new motor and not burn that one up but they have been out of production for many years and all spares have been eaten up. Presently the Tascam BR20 DC capstan motor which is a 12W motor is available although expensive. This motor comes with a connector on it that would be cut off and the motor soldered to the appropriate places on the servo board you have. I have done this a couple of times and it does work. You could also take your chances on E bay on a used one but they might be burned up or worn out as there is no way to tell.

 

[Adinol]

Thanks for the info, Skywave.

What would be a fair price to pay for a motor? I found a factory new EM1450 motor with the PCB, for $220. From what you are saying, this might be a rare find. But how much should I expect to pay for a BR20 motor? I actually can't seem to find any of those.

My other concern is that I don't know what burned the motor in the first place. I would hate to install a brand new motor and burn it as I power up the machine.

How concerned should I be about that?

Thanks...

 

[SkywaveTDR]

You can call Tascam parts and get a price on the BR20 capstan motor- it will be less than that $220 which is ridiculous pricing.
The motors burn up due to prolonged abuse as in trying to run a machine with a stuck or bad belt or one that is far too tight. I have found some unit with vacuum cleaner belts on the unit which were promptly removed- the local shop out there that JUST want your money often are full of idiots that have no clue how to fix a unit correctly. I have even caught them leaving insulator sheet off of heat sinked transistors. A used motor that is in good shape should not be more than $100 I would think. You can get used ones from Audio Pro in MA and Reelprosoundguys in the north west- I forget the state (Utah maybe) they are in but they can have these parts.

 

[Adinol]

Once again, thank you for tasking the time to help me. This is very useful info and I will contact those sources.

I am really just teaching my kid about analog audio and there is no rush. He is just fascinated with this great technology and my part of the job is to make it possible for him to explore.

Thanks again, for the information.

 

[SkywaveTDR]

If I was in the NY area I would get on the phone to New Jersey factory Service- owner Russ should be able to get you a BR20 motor. They are 12 watt and much more able to take abuse.
The idea with these motors is not to burn them up.
New Jersey Factory Service, Inc.
16 Chestnut Avenue Suite 103 B
Emerson,New Jersey 07630
201-967-0060
Mon- Wed 8-4 Thurs 8-2 Closed Fri Sat/Sun by appt.