8mm Forum: Question About Eumig S 802

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Posted by Dan Lail (Member # 18) on August 01, 2010, 07:30 PM:

My Eumig S 802 has a hum in the sound. I'm certain it needs new capacitors. Does anyone know how many capacitors it has and who might be able to replace them. I can remove the circuit board for shipment.

Posted by Brad Kimball (Member # 5) on August 01, 2010, 07:34 PM:

I have the same machine. Now I have something to look forward to. I haven't used it in about 4 years. Guess I should power her up and see if all is okay. Try getting in touch with Richard Patchet, Ken Layton or Phil Johnson.

Posted by Steve Klare (Member # 12) on August 01, 2010, 10:08 PM:

Hey Dan,

One of the classic things with the Eumig 800 Series is the famed Hum-Buck coils (-originally invented by Ebenezer Scrooge...BAH!). These are located near the heads and can be maneuvered around to minimize hum. Of course if they were already as good as could be they can only be maneuvered around to increase hum.

I replaced the main DC power supply capacitor on mine with a modern equivalent of even higher value and if it did help the hum, the difference was only slight. So if power supply ripple is a contributing factor, it' not the biggest one.

If you intend to replace those caps, I think you can do it yourself. If you replaced that Amplifier IC on your ST-1200, doing a couple of electrolytics is a piece of cake. The whole thing is getting the correct values and installing them with the polarity correct. If you get them backwards they tend to overheat and...you know....explode.

I was messing around with all of my projectors recently trying to design an interface circuit between projector audio outputs and stereo amp inputs and I measured the ground voltages of several of them to see how big a problem ground loops could be. As a result I found the 800 series Eumigs aren't very good in terms of how they are internally grounded. This isn't good where hum is concerned. I want to improve the grounding of mine and hopefully it will be less hummy.

I suspect another part of the problem here is that main power transformer is sitting unusually close to the heads, so the pickup of the transformer's stray magnetic field by the head and the resulting hum will be that much worse.

Posted by John W. Black (Member # 1082) on August 01, 2010, 10:13 PM:

Dan,are you still getting sound from the film or are you only getting the hum?

Posted by Dan Lail (Member # 18) on August 02, 2010, 01:04 AM:

Steve, I haven't taken a look at the coils or transformer yet, but I will investigate. So I can replace the caps myself. That's great. Could a magnetic shield be installed to isolate the transformer?

John, the sound works, but the hum gets very loud when I increase the volume.

Brad, I have Ken's contact info.

Thanks, all. [Smile]

Posted by Steve Klare (Member # 12) on August 02, 2010, 06:42 AM:

I think the metal wall of the machine should be pretty decent shielding in of itself, it's just that I wouldn't have put the transformer there if I designed the machine.

-Then again I was probably about 10 at the time, so nobody was asking!

(It's a pretty compact design: they may not have had too much choice.)

If there's anything I can do to help replace the capacitors, please ask. I can identify them and help you find replacements too.

Posted by Dan Lail (Member # 18) on August 02, 2010, 10:50 AM:

Thanks, Steve! I'll post a pic of the circuit board.

Posted by Dan Lail (Member # 18) on August 04, 2010, 02:57 PM:

Steve,

Looks like I'll be sending the circuit board to Ken.

Posted by Simon Turner (Member # 2146) on August 08, 2010, 11:44 AM:

from what you describe it is failed capacitors, you have to make sure you put the correct voltage in. modern caps are far more robust I guess but you should still allow at least 150% of the nominal voltage, I've seen old stuff with too low voltage caps as the correct values where probably very expensive or non existent in the day. I recently fixed my dad's quad amp and the values fell a bit short of the recommended, then i took a look at a friends failed engine analyser and same there

Posted by Steve Klare (Member # 12) on August 08, 2010, 12:59 PM:

They say electrolytic capacitors gradually dry out with age and the capacitance values fall. Smaller caps like ceramics and polyesters have their own aging issues, but not nearly as dramatic ones.

A few years back I worked for Lambda Electronics, the power supply manufacturer. They had a policy with old stock and field returns over five years old that whether the thing was a ripple failure or not, they'd replace all the electrolytics before it went out to a customer.

-but, when I looked at the electrolytics on my 20+ year old Eumig they were still within tolerance and replacing them didn't de-hum the machine either.

So, this is a good idea, but it may only be one step in the total fix.

Posted by Tony Stucchio (Member # 519) on August 08, 2010, 07:01 PM:

You may want to try a flux capacitor...
[Big Grin]

Posted by Dan Lail (Member # 18) on November 09, 2010, 11:53 PM:

Okay! I am back to explain the experience. [Big Grin]

I had all the capacitors replaced including the electrolytic cap. The hum is still the same. The hum is loud and clear and the sound from the film is low and muffled. If I unplug the the sound board from the magnetic sound heads and turn the volume control up, there is very low(normal) hum and a clean sounding amp.

The people who love these Eumigs can't possibly be accepting this awful sound.

What gives Beav.

Posted by frank arnstein (Member # 330) on November 12, 2010, 04:49 PM:

Dan,

As has been suggested by Steve,,,,,
Have you tried adjusting the 2 cursed Eumig "Hum Buck Coils" ????

The coils really do make a difference to the hum & if they have been moved slightly from where they were set, then the projector will hum. You need to move the coils around while the projector amplifier is turned on, rotating them or moving them a bit. Do this with the sound turned on & listen to the humming sound while you adjust the coils.
You will notice a reduction in the hum when the correct coil angles are achieved. It takes a bit of time to get it right.

Re the issue with the broken front spindle....
The pics dont show the missing piece of the delivery spindle but as its a dual projector then the front spindle needs to have the thin section spindle which can take Standard Eight reels.

A removable collar brings the diameter up to Super 8mm size, so you need that collar too. The pic of the rear spindle shows its the Super 8 size but this is not what the broken-off front spindle looks like. It is thinner so it can also take reg. 8mm reels.
You should be able to locate a spare front dual spindle from one of the forum members.

Good luck with it...

dogtor frankarnstein
[Razz]

Posted by Dan Lail (Member # 18) on November 15, 2010, 10:28 PM:

Thanks, Doc. I did try all suggestions, but no success. Then I got out the old contact cleaner and bathed the pots and the record function on the circuit board. Wow,wow, wow!!!! Success! All hum is gone and the volume is nice and loud. Sounds like new.

Thanks to all. [Smile]

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