8mm Forum: Debrie D16

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Posted by Terry Sills (Member # 3309) on October 20, 2015, 02:08 AM:

I have mains hum when the motor is running but the amp is fine when motor is off. Does anyone have any idea how to remedy this fault? Is there a suppressor for the motor that may have failed and if so where is it located. Any help much appreciated as it is my favourite 16mm projector.

Posted by Thijs de Kort (Member # 4897) on October 20, 2015, 04:09 AM:

Hey Terry,
Have you checked if the ''record'' isnt switched on? this usually prevents the sound from playing even if you aint recording anything.
Thijs

Posted by Terry Sills (Member # 3309) on October 20, 2015, 12:07 PM:

Thijs
The projector doesn't have a record switch. It is just for playing 16mm optical film.
I do get sound when playing film but accompanied by the 'hum'. The louder I set the volume, the louder the hum.

Posted by Maurice Leakey (Member # 916) on October 21, 2015, 02:42 AM:

Terry

The Debrie D16 has a synchronous motor and does not have a suppressor. Earlier types of motor with bruahes needed a suppressor, however, this was for suppression of sparks from the brushes, probably causing noise and interference on your neighbour's radio or television.

The Debrie's motor probably has a starting capacitor. This uses a "discharge" but is unlikely to cause a hum. Any hum is probably a 50 Hz hum often caused by a breakdown of smoothing in the amplifier.

Is the hum present when the motor is running without the lamp? Or only when the lamp is on? I assume your projector is standard and not modified in any way

I am sorry that this reply doesn't really answer your problem.

Posted by Terry Sills (Member # 3309) on October 21, 2015, 12:16 PM:

Thanks for the info Maurice. The hum is there when the motor is switched on without and with the lamp, which is why I assumed that it was a suppressor. It is a completely standard machine without any mods. As the hum is only associated with the motor isn't it possible that something governing the hum has broken down?

Posted by Maurice Leakey (Member # 916) on October 21, 2015, 02:43 PM:

I can't see how the motor can cause the hum. One thought is the P.E.C. Perhaps there is some vibration causing it to translate it as a hum.
Take off the P.E.C. cover and gently withdraw the cell. Has the hum gone? Carefully clean its pins before replacing.

Posted by Terry Sills (Member # 3309) on October 22, 2015, 07:29 AM:

Maurice
Tried what you suggested - no difference. Even with the pec removed the hum
starts as soon as the motor is switched on and stops as soon as the motor is switched off. So it has to be related to the motor. There is a big green resistor/capacitor fitted in the housing above the pec. Could it be something to do with that?

Posted by Maurice Leakey (Member # 916) on October 22, 2015, 08:55 AM:

I assume that the capacitor to which you refer is the starting capacitor, i.e., when motor is switched on the capacitor charges up and then discharges across the motor to "kick-start" it. Thereafter, it can run by itself
Perhaps you could change the capacitor. It's worth a try.

Posted by Neil Massey (Member # 5081) on October 25, 2015, 11:46 AM:

I had hum problems with my D16 which I had when I first got into 16mm. The symptoms were a need to increase the volume after about an hour and an increase in background hum when running. When it wasn't running, the hum was negligible. My father (who was an electronics expert) attributed this to the capacitors in the amp going so the whole amp was overhauled with new valves (tubes) and p.e.c. Despite all this work - no difference.

It was eventually traced to a problem in the screening around the p.e.c contact on the amp. We removed the projector head and then with the base amp warmed up, turned the switch to motor then lamp positions so the contacts on the amplifier base became live - as soon as we did - the hum appeared. The solution was to bypass the usual route for the p.e.c and use a screened lead that went from the p.e.c directly to a socket on the side of the amp (coming out through the hole for adjusting the voltage for the cell.

That solved the hum and volume problem once and for all. I can't help but wonder if this was a bit of design fault as I notice that the last of the D16 design with a transistor amp had a fixed base. Anyway, if I am ever lucky enough to own another one then I would look to do the same modification.

Hope this helps.

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