8mm Forum: Sound Problem with Eumig S 912 GL

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Posted by Chris Ballantyne (Member # 4502) on April 21, 2015, 10:26 AM:

Hi, I recently bought a Eumig S 912 GL projector with the sound not working. When I opened up the back, it was in very good condition. There was however a transistor that was broken which I replaced. There was also a small section of red wire just lying on the circuit board. I have checked all over the projector, and there doesn't appear to be any wire missing from anywhere, but it was lying underneath a small red coil, which is next to a white coil of the same type of wire.

I tried the projector with a flim afterwards and it still didn't work, so I went back inside, took the circuit board out and checked each component. Everything seemed to be in working order. So I put it all back together again, tried it with a different film and it worked brilliantly.

So I put the original film I tested it with back in and that worked too, for a short time. After a minute or so, the sound just stopped, and I haven't been able to get it working again since. Apart from the sound, the projector works brilliantly.

If anyone has any idea what could be wrong, I would appreciate some help.

I could also use a manual for it, if anyone has a link for one.

Thanks,
Chris

Posted by Steve Klare (Member # 12) on April 21, 2015, 10:51 AM:

My best guess is some flaky connection somewhere: some oxidized connector pin, some not quite there solder joint, some switch that's asleep on the job.

When you turn up the volume, do you hear hum in the speaker?

Posted by Maurizio Di Cintio (Member # 144) on April 21, 2015, 01:13 PM:

Steve, some EUmigs of the Series 900 have sound muting when in stop mode. To perform the check you suggested, Chris might need to switch the projector to FWD projection mode (Lamp on) with no film: this way if everything is OK with the sound board, he'll hear hum (max volume).

Posted by Steve Klare (Member # 12) on April 21, 2015, 01:26 PM:

-and that could be a reason the machine is silent:

Maybe whatever switch contact is supposed to tell the sound board it's time for sound...isn't!

(Captain Scott was right: "The more they overthink the plumbing...")

Posted by Chris Ballantyne (Member # 4502) on April 21, 2015, 03:04 PM:

I definitely hear a sort of hum when I have it on full volume, but it sounds more like a hiss.

Ive played with all the switches associated with sound to see if I can free them up, but nothing. Could it be something to do with the pickup head? Maybe give it a good clean?

If it helps diagnose the problem, I can try and get some pictures of the insides up too.

Posted by Steve Klare (Member # 12) on April 21, 2015, 03:29 PM:

Yes, the hum often incudes some hiss.

-but, from this you know the amp is getting power, and it's connected to the speaker, which is working too.

Can you plug in a headphone and see if you get audio?

If you put in a sound film and play it with the volume set full blast, do you hear even a whisper of sound track?

Posted by Chris Ballantyne (Member # 4502) on April 21, 2015, 03:36 PM:

Nope, nothing but a hiss from the speaker. Just double checked too. I've pluged an external speaker into the headphone socket too to check if something was going wrong with the speaker, but nothing through there either.

Posted by Steve Klare (Member # 12) on April 21, 2015, 03:57 PM:

The fact that you are getting hiss and hum and can control it with your volume control means your power amp is working too.

-at that rate it's starting to sound like the sound head, the connection between the head and the pre-amp, or the pre-amp itself.

-OR:

When you run the film in regular projection mode, is it being pressed down on the sound head?

Posted by Chris Ballantyne (Member # 4502) on April 21, 2015, 04:11 PM:

Well, when I put it on to play sound, there is a little arm that moves up to pinch the film between what looks like two rollers. The roller on the top is connected to a big metal flywheel in the back of the projector.

I'm guessing when the arm moves up, that is the sound head it is pressing the film against?

Posted by Maurizio Di Cintio (Member # 144) on April 24, 2015, 03:26 PM:

The sound head is located before the two rollers (metal/rubber) and the sound pressers lie inside an encased assembly placed right below the lamp holder. To access the sound presser for inspection/clenaing pull the red square thingy up by means of a tiny screw driver; the assembly will open up (actually the pressers cartridge will move downward a little) and you can inspect or clean. There might be a lose connector or a problem in some wiring in this area and the signal from the head will not reach the amp stage. Unless, like Steve seems to be hinting at, the head has gone...

The problem in this case is to assess the actual degree of head wear and this is very difficult because of the position of the head; perhaps you can find and use a dentist's circular mirror, provided it is small enough to fit in and it is made of plastic. If the head is gone, you will notice a gap in the head so "wide" that it looks like the metal prong of the head is clearly severed in the middle. This is easier to spot if you also use a very narrow spot light/torch.

Posted by Chris Ballantyne (Member # 4502) on April 25, 2015, 02:50 PM:

I see what you mean about it being hard to see if it's worn. Is there a way to remove it to inspect/replace it?

If I can remove it, I should be able to get a picture of it on here.

Also, if it's worn, are there replacements for it out there?

Thanks

Posted by Maurizio Di Cintio (Member # 144) on April 26, 2015, 02:58 PM:

You don't want to remove if it isn't necessary and you can only know by getting the kind of mirror I suggested and a small flashlight (mini "MAG-Light work wonderfully because you can focus the light beam exactly on the very narrow spot you want to light).

I might supply you a semi-new head but first you have to know if that is the problem.

If, through careful inspection, you notice the head is not just a little recessed in its gap but there is actually a GAP (meaning an interruption right at the center of the contact surface with the stripe), then the head can be disposed of. But I doubt: these heads are somewhat soft, but the main stripe head usually has a life much longer than the balance track head because it's less narrow. Keep us posted!

Posted by Chris Ballantyne (Member # 4502) on April 29, 2015, 01:13 PM:

When I head back home at the weekend, I'll have a look with the mirror as my dad has one at home. Thanks for the advice!

Posted by Chris Ballantyne (Member # 4502) on May 02, 2015, 09:38 AM:

Well, I've gone and left the projector down in Hull... I guess the mirror will have to come back down with me then!

Posted by Chris Ballantyne (Member # 4502) on May 17, 2015, 01:45 PM:

Turns out my dad's inspection mirror is too big. I've found a 20mm one online, so I'll get that and hopefully be able to examine it in a few days time.

http://uk.rs-online.com/web/p/inspection-mirror-probes/0394162/

Posted by Chris Ballantyne (Member # 4502) on May 19, 2015, 12:46 PM:

Well, I've had a look with the mirror. There seems to be a gep perpendicular to the direction of film travel. Not sure if thats the gap you were talking about. I've taken a picture and will upload it, if I can.

Don't know how to upload it directly, heres the link:

https://www.flickr.com/photos/124784028@N05/17245157554/in/dateposted-public/

I've put a red circle around what I saw.

Posted by Chris Ballantyne (Member # 4502) on May 23, 2015, 03:50 PM:

Okay, it's definitely an intermittent fault. I had the sound working tonight, but it's stopped again. It was playing fine on my desk, so I took it through to the kitchen to project on a bigger area, and when I turned it back on it wasn't working again. All I did was fiddle with some wires and check their continuity.

I'm quite puzzled now...

Posted by Andrew Woodcock (Member # 3260) on May 23, 2015, 03:55 PM:

When my pj was doing similar it was a dry joint problem.
Quite common on older circuit boards and nearly always results in an intermittent fault rather than anything conclusive.

Usually the hardest to diagnose also.

http://www.praudio.co.uk/other-repairs-beaulieu.htm

No problems whatsoever since, I am pleased to say.

[ May 23, 2015, 05:42 PM: Message edited by: Andrew Woodcock ]

Posted by Chris Ballantyne (Member # 4502) on May 25, 2015, 01:16 PM:

Going to have another look at it after next Monday, going to focus on revising for my exam.

I'll go over everything I looked at, this time with the projector on, so when I get to the thing that fixed it, I will know what was wrong.

I'll let you know how it goes!

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