8mm Forum: Magnetic Sound Pickup Issues

This is topic Magnetic Sound Pickup Issues in forum 16mm Forum at 8mm Forum.

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Posted by Hugh Burch (Member # 4342) on July 09, 2014, 05:08 AM:

Hey,
I am currently in the process of testing and if necessary fixing sone old projectors, most of the issues are straight forward but there is one i am stuck on.

I have an Elf Eiko Sound Rm-2 which is in good working order except that it wont pick up magnetic sound. Testing is being done with a professional sound test reel so thats not an issue and I have opened it up and checked all circuit boards, cables and connections, all of which look fine.

If anyone has one of these, or experience in fixing them I would be grateful of a shunt in the right direction.

Thanks
Hugh

Posted by Maurice Leakey (Member # 916) on July 10, 2014, 02:47 AM:

Most 16mm projectors which are optical & magnetic have spent a great part of their lives projecting optical films.

It is possible that the contacts on the Opt/Mag switch have corroded through non-use.

You could try flipping the switch backwards and forwards some dozen to twenty times in an effort the "clean" the contacts.

If the optical side is operating correctly there seems to be somewhere where the magnetic signal is getting lost.

Posted by Paul Mason (Member # 4015) on July 10, 2014, 03:12 AM:

Hugh,
You really need a a service manual for the RM-2 or failing that an RM-1 to show the extra bits used for mag playback. Almost certainly there is magnetic preamp circuit board. Try and inject a signal into the preamp to see if it still works as the mag head may have failed or the wiring from the head to the preamp gone open-circuit.

Posted by Hugh Burch (Member # 4342) on July 10, 2014, 05:47 AM:

thanks guys,
i will investigate the circuits a bit more. but how can I safely run a signal through the magnetic circuit? would I need to match the current some how? I imagine I couldnt just attach my ipod via a butchered phono cable for example?

i have found a couple of service manuals for either this projector or similar but cant see anything usefull, if anyone wants to have a look?

http://www.acofs.org.au/part_5_files/Eiki/Tech%20R%20series.PDF

http://www.k3camera.com/pdfs/eiki/2009-eiki-slii-service-manual.pdf

thanks

Posted by Paul Mason (Member # 4015) on July 10, 2014, 07:43 AM:

Hugh,
You need a test signal oscillator that only generates a tiny (less than 1 volt) signal at say 1000 Hz. Maplin sell multimeters which have them built in. Don't use anything like a smart phone that might damage the circuits or itself and be careful of mains voltages when the projector is plugged in and you have the back open.

Posted by Martin Jones (Member # 1163) on July 10, 2014, 09:20 AM:

Or simply use an insulated screwdriver held between finger and thumb (professional method)on the point where the head connects to the rest of the circuitry. A loud hum should be heard.

This kind of signal is very small .... a multimeter oscillator output will be MUCH too high ... just what is needed at this point in the circuit.

Martin

Posted by Hugh Burch (Member # 4342) on July 10, 2014, 09:20 AM:

i have sorted the problem, thanks for help.
the magnetic pickup wasn't making the connection on the film. so adjusted it a bit and is now working fine.

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