Radionette(Tecsonic) capstanmotor problems.

Hello,


I am in the process of restoring a Radionette RN-236, a.k.a Tecsonic MX-900E.

The problem I have is that both tapedecks are playing too slow.
The drivebelts are new, and everything is running smoothly.

I have 12,3V to both motors.

There is no speed adjustement on the back of the motors.
They have 4 connectors, +,-,A and B.
According to some googlesearching, the A and B are for speed control at normal and highspeed operation.
There are wires coming from a small circuitboard, to pins A and B, with 4 adjustable pots.
I have tried adjusting them, but the voltage they put out does not change and the motors do not change speed.

Should I be able to adjust the speed on these, or are they for something else?

I find it strange that both motors could be defective and operate at the same speed, or is it common?

Has anybody been able to fix such a problem, or should I try new motors?

/Henrik

Each motors have a small stickers on back side.
Sticker of one motor is torn.
Maybe have small hole to ajust the speed....

The tear in the sticker was me.
I removed the backplate completely from the motor, but there was nothing to adjust on the inside.

They are a 4 pin motor so do have some control of speed IF there are 4 wires going to them?
If you look on the small motor pcb and follow the wires, the ones which control the speed should lead you to a trim pot.
Red and black are likely to be v+ and ground, see the colours of the wires.

docs said:

They are a 4 pin motor so do have some control of speed IF there are 4 wires going to them?
If you look on the small motor pcb and follow the wires, the ones which control the speed should lead you to a trim pot.
Red and black are likely to be v+ and ground, see the colours of the wires.

Click to expand...

Yep.
White and red on the motors are + and - supply voltage, 12,53V.
A and B are connected to the small board via the yellow and green wires. There are four pots, two for each motor.
On the yellow i have 9.8V and on the green one 11,8V.
If I change the settings on the pots nothing happens, the output vltage on the yellow and green wires stay the same.

I did try to short the red wire to the green, upping the 11,8V to 12,53V and the motor ran even slower.

It is a bit of a "hack job", but i could add a turn pot to the green wire and drop the voltage(11,8V). In theory that would speed up the motor since upping the voltage slowed it down.

But I would rather find the root to the problem.
I have searched the net, but I cant find a servicemanual for any of the a.k.a:s of this boombox. It would be nice to have a schematic to look at.

Did you test the trim pot ti see if it matches its marked rating? Should say 3k ir something like that in it.

The trimpots said 200Ω and 500Ω.

Desoldered them and the 200Ω measured about 230Ω
The 500Ω one measured 3,9KΩ so I replaced it with a correct one, but there was no difference.
Desoldered them again and turned on the pots while measuring, there was no difference in resistance at all over the pots travel.

I replaced both pots with a single one that did adjust from 0-1.5KΩ, but that did no difference either.
I detached the yellow and green wires from one motor and measured on the A and B connections.
The 9.8V and 11.8V where still present, the motor itself seems to generate them.

Then I soldered a trim pot between A and B pins, and now I was able to adjust the speed.
Around 550Ω gave me the correct speed.

I am guessing that the small board, with the four pots, and the yellow/green wires have something to do with high/low dubbingspeed perhaps.

Atleast now I can listen to tapes for the time being.

A fix is better than nothing no matter how you got there so well done.