8mm Forum: EUMIG 712D

This is topic EUMIG 712D - no sound in forum 8mm Forum at 8mm Forum.

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Posted by John Shuttleworth (Member # 4594) on June 04, 2019, 02:51 PM:

I have managed to get this old projector running at a steady speed in both directions but have no sound, hum or even the odd click from the speaker. Does anyone have access to a circuit diagram for the amplifier please?

Posted by Maurice Leakey (Member # 916) on June 04, 2019, 03:05 PM:

I know this is a stupid question, John, but have you turned on the amplifier?

Posted by John Shuttleworth (Member # 4594) on June 04, 2019, 03:16 PM:

Thanks for the prompt response, Maurice. Not a stupid question at all but as far as I can see, there is no switch and the volume control does not include a switch either. The tone control does but it seems that it is not an on/off switch but is for automatic recording level.

Posted by Maurice Leakey (Member # 916) on June 04, 2019, 03:20 PM:

It was a suggestion as I have an earlier model with a valve amp and the volume control has an on/off switch.
You could open the back and see if the leads to the speaker are firmly connected, I believe that the speaker leads mate with the main body when the back is in position.

Posted by John Shuttleworth (Member # 4594) on June 04, 2019, 03:30 PM:

Thanks Maurice. Mine is a transistor amplifier and I have already checked the speaker and external speaker connection socket. This is why I feel a circuit diagram would be helpful. Let's see what the forum members come up with.

Posted by Maurice Leakey (Member # 916) on June 04, 2019, 03:34 PM:

My last suggestion is to use the record button several times to clean the contacts as when in record mode the speaker circuit is often muted in similar projectors.

Posted by John Shuttleworth (Member # 4594) on June 04, 2019, 03:50 PM:

If this is the big red square button on the left hand side then yes, done this and also sprayed contact cleaner for good measure, but all to no avail. Incidentally, this projector unusually has an A1/17 bulb which I have not seen on other similar Eumigs.

Posted by Leonard Goss (Member # 3172) on June 04, 2019, 03:59 PM:

Also insert a plug in and out of the external speaker socket a few times, this may clean any dirty contacts.

Posted by Will Trenfield (Member # 5321) on June 04, 2019, 05:41 PM:

I have one of these fifty year old machines with the same problem. I couldn't find the fault but found that I could connect the projector to an external amplifier for sound. Unlike other Eumigs in the 700 series, this model used the A1/17 "Spaceman" 8v 50w bulb as standard.

Posted by frank arnstein (Member # 330) on June 05, 2019, 02:20 AM:

Hi John

there were two versions of amplifier in this 700 series.
One is 2w and the other is 3w.

See if you can find out which one you have as the circuit diagrams are different. Maybe it's written on the rear specs plate.

Dogtor Frankarnstein
[Smile]

Posted by John Shuttleworth (Member # 4594) on June 05, 2019, 11:03 AM:

Thanks Will. At least I now know the bulb is the correct one.

Hi Frank. I have just had a good look and can't see a way of identifying which version I have. There is nothing on the rear plate and no markings near the speaker or ext. speaker connection or indeed on the amplifier itself. If you have access to both diagrams I will be able to take it from there.

Cheers both.

John

Posted by frank arnstein (Member # 330) on June 05, 2019, 08:09 PM:

Hi John,

I have taken the following data from the Eumig 710d factory repair manual....perhaps this will help identify your machine.

"In the 2 watt version, the power amplifier consists of the complementary transistors AC 187 K and AC 188 K and in the 3 watt version of the integrated circuit, LA 4031."

I have scanned the 2 circuit diagrams for you and emailed them.

Dogtor Frankarnstein [Wink]

Posted by Luigi Castellitto (Member # 3759) on June 07, 2019, 08:46 PM:

John, try to follow this procedure by repeatedly pressing the rec button as indicated.

http://8mmforum.film-tech.com/cgi-bin/ubb/ultimatebb.cgi?ubb=next_topic;f=1;t=008026;go=newer

I could not find old discussions where, I remember, it was said to press the rec button several times (without breaking it!) To reactivate the sound on the Eumigs.

Posted by Lee Mannering (Member # 728) on June 08, 2019, 02:10 AM:

Morning John.

My 50 year old 712D is still going (part of what I call the UK Eumig Museum, even I'm in it!) BUT they started to need work as the old transistor amplifiers are well old.
Yes you can turn the main control knob to reverse and push the red record button a few times but before you do this I would give the switch block a squirt of SWITCH CLEANER which will also lubricate the old contacts which may be oxidised somewhat.

The switch is located in the back on the machine at the other end of the steel switch cable. You will need to tilt the projector when doing this to get the cleaner to run down the contact block.

Also squirt the switch which is inside the lamp house.

With the age of projectors now many Capacitors are starting to fail. The blessing is the little Eumig does no have that many in but usually I find its the big one right next to the speaker connectors at the edge of the circuit board. You cant miss it.

Off topic. My electronic home organ expensive in 1990 suffered capacitor trouble and I had 86 caps to change out to get her going again. As a footnote for more recent cine projectors from the 80's and early 90's may contain the troublesome SHRINK WRAPPED CAPS which will leak like mad, usually all over the circuit board so watch for these. Japan started using cheap China Caps at the time in penny saving measures but at least we can spot the trouble just by looking.

Back on track. If all the switch cleaning fails John and you still are not hearing at least a hum from the speaker when running the 710D change that large capacitor, if it has gone for any reason you will hear nothing from the projector.

Good luck.

Posted by John Shuttleworth (Member # 4594) on June 08, 2019, 10:14 AM:

Thanks, guys, for all your help, suggestions and advice. I now have the circuit diagrams as well so I am well placed to tackle the amplifier fault. I am shortly away on my travels for a week but will definitely devote some time to this on my return and will let you all knwo in this thread how I get on.

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