8mm Forum: Eumig Mark S 810D Lux sound problem

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Posted by Luke Coiro (Member # 1380) on November 02, 2012, 03:09 AM:

I recently aquired a Eumig Mark S 810D Lux projector and it runs films well but initially there was no sound... just humming. I took off the front cover and examined the N-S switch and noticed a wire had come off from one of the terminals so I soldered it back on and now I have sound, however the hum is still there. So far I have been testing Super 8 films with sound and all the same. Also tested the line out and hum is present too so the speaker seems fine. I read on another post that moving the record switch in and out while on reverse as well and moving the knobs to remove any build up helps along with spaying them with contact cleaner. Tried all that but the hum is still there. The hum is on sometimes with the reverse or forward settings but mostly and more loudly on the foward/lamp setting. I checked the wiring on the N-S switch to see if there were any shorts but all looks ok. Any ideas of how to get rid of this hum?

Posted by Martin Jones (Member # 1163) on November 02, 2012, 04:19 AM:

On this machine, in the vicinity of the lamp/soundhead/changeover switch there are two little coils of wire on plastic formers mounted on flexible spring arms. The purpose of these coils (hum-bucking coils) is to INTRODUCE hum into the head circuit, the idea being that, depending on the position of the coils, the INTRODUCED hum can be adjusted to OPPOSE, and hopefully CANCEL, the natural hum.
These are carefully set in the factory, but even a change of lamp can affect the setting. Someone may have previously tried adjusting these and made it worse, so I suggest that you try VERY small adjustments of each coil in turn, monitoring the effect on hum on ALL settings of the switch and direction of travel of the machine. Keep the same setting of volume control at all times so that your comparison is valid.
You may yourself have disturbed them in repairing the broken lead, so this is a valid thing to try... but put them back where they were if you can get no improvement. There are, of course, other causes of excessive hum.
For your pin problem..... ouch! I can only suggest that you look for scrap machines with whole pins, unless you can find someone with the skill to insert new pins (based on measurements of the one on your 810D) into the brass mounts on the claw arms. BUT... don't remove the 810 claw arm from the machine if it's running properly, the setting is critical when re-fitting it. You will have to experiment with the replacement or repaired claws when replacing into the 824s.
Martin

Posted by Lee Mannering (Member # 728) on November 02, 2012, 04:31 AM:

Luke. It could also be the red record switch on the back which is linked by a wire down to the amplifier board.
Try this. With the machine un plugged turn the main control knob to reverse then push the red record button in and out several times.
If the above does not work it may well be the coils which are near the sound head block as Martin proposes. One coil is for Standard 8 and the other for Super 8. If the level of hum is exactly the same when you switch the sound head over (black switch) I guess you may have another fault.

Posted by Luke Coiro (Member # 1380) on November 02, 2012, 07:43 PM:

Thanks Martin for the tip. I had a go at moving around the coils and in super 8 mode noticed the coil to the right of the N-S switch did affect the hum. I got it in a position that reduced the hum considerably but not completely gone so I'm on the right track. Also played around with the record button in reverse as Lee advised & that helped a little too. Seems like ancient technology using coils to control the hum but then this machine is around 40 years old.

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