Sony DTC750 DAT mechanism problems

[Marconi_MPT4]

Problem started with random stopping during play which steadily deteriorated into being unable to play a tape, the cause being take up spool stalling allowing the tape to loop out.

Eventually I managed to identify there was very weak torque produced by the reel motor. Disconnecting motor from the circuitry, removed belt and applied about 3 volts allowed the motor to run at a reasonable speed drawing about 20mA. Loading the motor, just slightly, caused it to stall. Running the motor for an hour or so made no difference. There were no obvious discontinuities in the commutator.

Is this a common problem with this motor or mech? Anything else I should check?

Some pics attached, the second one showing Mabuchi RF-3.. 5.9v motor

Cheers

Rich

[MikeyPP]

Reel motors do fail on them, but you should also check back tension with a test tape for a proper job.
(Excess back tension will also prematurely wear the drum.)
They used to do a kit which included a new reel motor iirc

[Marconi_MPT4]

Hi MikeyPP

Thanks for information regarding repair kit. The service manual shows there was a modification to the electronic torque control circuit suggesting a problem around this area.

A quick search reveals the motor is one of the few parts available now but is available at a price from Charles Hyde on back order.

Given the uncertainty of how much life left in the head (c.£500 for a head block assembly) the recorder will have to sit in the pending pile for now to see if I can obtain a scrap or good second hand unit.

Cheers

Rich

[MikeyPP]

random stopping during play

Could be that reel motor is knackered but that's actually also a documented symptom of excessive back tension.
Without the ability to check/confirm and adjust the backtension I'd say you're working in the dark though.
I've actually got half a dozen of these things waiting to be looked at for a friend (and I do have the torque/back tension cassette)

[jamesperrett]

I had a similar problem with the take up reel not turning on a DTC500ES and I understand that it is a common issue. Mine seemed worse if the tape was loose after winding or rewinding.

James.

[ben]

That motor in the second pic looks pretty bog standard to me, I'm surprised they didn't use something a bit more decent.
If th¡s is indeed at fault, the good thing is that it does not seem machine-specific, looking a bit 'off the shelf' at least in mounting. Hopefully you'll find a replacement.

[Red to black]

That motor in the second pic looks pretty bog standard to me,

Hi ben,

I was just thinking the exact same thing, it looks nothing special, I was expecting to see a flat pack VCR type DD capstan motor affair, that motor just looks like a 'cheap' bog standard reel motor as used on cheap cassette mechs.

Cheers,
Baz

[Michael Maurice]

What happens if you run the motor at 5V or 5.5V? If it still stalls then motor is knackered otherwise it might be that 3V is too low for it.

[Marconi_MPT4]

Originally Posted by Michael Maurice

What happens if you run the motor at 5V or 5.5V? If it still stalls then motor is knackered otherwise it might be that 3V is too low for it.

I managed to get some time last week to try the motor at 5 volts and it is still sadly lacking any torque. The original test voltage of 3 volts was chosen as shown in the DTC750 manual, here it is 2.6 volts.

Thanks for all comments and agree the quality of motor used by Sony is poor. All tests point to a failed motor. It should be easy to find something to fit as this type of motor appears to be commonly used as spin motors in cheap £17 DVD players! One of the later modifications Sony did to the drive circuit was to make it adjustable by reducing R360 to 22k and adding a 47k pot in series. Interestingly at the same time the torque setting was changed from 10 ~ 20g/cm to 10 ~ 16g/cm and back tension from 5 ~ 6g/cm to 4 ~ 5g/cm.

Again many thanks.

Cheers

Rich

[MikeyPP]

as this type of motor appears to be commonly used as spin motors

Make sure the D/V spec on the label of your chosen motor match the D/V spec on the original

Spindle motors and sled/reel motors have different characteristics and this one needs to match

[TIMTAPE]

If a motor has consistent but weak torque at the stated voltage it's usually because of binding bearings. Is the shaft hard to turn with no voltage applied or does it spin freely? Sometimes a tiny drop of light oil in each bearing will free the bearings up. Might save you the trouble of having to source another motor.

Tim