8mm Forum: Elmo ST-1200D M&O Sound Distortion Problem

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Posted by Christian Schatz (Member # 2961) on December 20, 2012, 05:56 PM:

Hello,

today i received my Elmo ST-1200D M&O with 1.1 lens. A really
nice machine. But i have a problem: the magnetic sound is
extremely distorted through the internal speaker, monitor
and aux out. If i use monitor out or aux out, the volume
knob funticon is normal, only sound distortion. If i use the
internal speaker, the volume knob causes dropouts in the sound
and the distortion is greater than over moni/aux out.

I cleaned the entire projector carefully, but the problem
remains. I hope that someone can help me to repair it.

Kind regards,
Chris

Posted by Pasquale DAlessio (Member # 2052) on December 20, 2012, 06:02 PM:

Christian

Did you try cleaning the volume control itself?

PatD

Posted by Christian Schatz (Member # 2961) on December 20, 2012, 06:14 PM:

Hey Pasquale,

yes, i cleaned the volume control. As i wrote, volume control function is normal if i use moni or aux out, only if i use the internal speaker it causes dropouts. But the biggest problem is the heavy distortion (too loud and overdriven). Do you think the volume control can cause that?

Posted by Pasquale DAlessio (Member # 2052) on December 20, 2012, 07:03 PM:

Yes. The volume control is a potentiometer. If it does not control the volume but instead remains in a loud setting, your sound will be distorted.

Posted by Christian Schatz (Member # 2961) on December 21, 2012, 04:15 AM:

Mh ok. I will clean it again. I will reply the result.
Thank you! [Smile]

Edit:

I cleaned the potentiometer volume control and now it can be adjusted and sound has no dropouts. But the sound is still heavily distorted. I think the film guide isn't fine, too. [Frown]

[ December 21, 2012, 06:01 AM: Message edited by: Christian Schatz ]

Posted by Vidar Olavesen (Member # 3354) on December 21, 2012, 09:12 AM:

My optical is a bit "rumbley" too ... It wasn't enough for me not to enjoy Memories of Me, but it was noticeable

I had drop outs too, but it wasn't the volume control, it was the lens for the optical sound ... Anyone know what kind of bulbs this optical part uses?

Posted by Christian Schatz (Member # 2961) on December 21, 2012, 09:43 AM:

I recorded a little video to show you the problem:
http://www.youtube.com/watch?v=6k0hCF-u8Ro

Posted by Jim Schrader (Member # 9) on December 21, 2012, 09:49 AM:

is it with all magnetic films?? try an optical print if you have one, check your speaker maybe that is bad??

Posted by Winbert Hutahaean (Member # 58) on December 21, 2012, 09:56 AM:

The sound amplifier might have been kaput.

As Jim says above, check with optical print if the sound is OK then the sound amplifier is OK too.

It can be also the sound head is kaput, in this case playing the optical print will be fine.

Posted by Christian Schatz (Member # 2961) on December 21, 2012, 05:42 PM:

Sadly i have no optical print in my collection.

I cleaned the circuit again. If i connect PC Speaker into AUX OUT or MONI there are no sound dropouts and almost none distortion. Looks fine.

I connected another internal speaker to the projector. Same issue like the original speaker: sound dropouts and heavy distortion like in my video.

It seems that the soundhead is not defective. The speaker seems not defective, too. And the sound amplifier? If the sound amplifier is defective, there would be the same problems over AUX OUT or MONI, right?

Posted by Steve Klare (Member # 12) on December 21, 2012, 06:13 PM:

Hi Christian,

The ST-1200's internal speaker and the external speaker jack are connected to the rest on the machine by a set of contacts that are pressed together when the back cover is put on. There is no wire on a plug like many other Elmos.

No guarantees, but it wouldn't cost a thing to take the back off the machine and polish these up, maybe bent them straight if they are curved inward. At the same time you could clean the contacts on the printed circuit board they press on too.

It's also a classic Elmo thing to work every switch associated with sound about 10 times when you have sound issues. This fixes these problems quite often.

On my ST-1200 I've heard the machine make all sorts of weird sound effects that were fixed by doing this. I fixed most troubles by removing the record key switch from the circuit entirely. I don't record with this machine: what do I care?

The problem you run into is Elmo used switches meant for 115V and higher on circuits with very low voltage and power like sound circuits. This doesn't break the oxide film on the contacts and they are no longer good conductors given time. Repeated switching often busts the oxide layer.

Why did they do this? Switches meant for low levels have gold plated contacts (gold doesn't oxidize) and gold costs a lot more than the nickel silver contacts on the high voltage ones.

-Good Luck!

Posted by Hugh Thompson Scott (Member # 2922) on December 21, 2012, 07:46 PM:

I had a similar problem years ago on my first ST1200, the volume
control being very noisy and hissy when adjusted. The result was
when I switched off the vol. control, then turned it back on the amplifier just faded and died. Luckily, the amplifier was quite a common one, and a trip to the HiFi repairer round the corner
sorted the problem for less than £20.00.I suspect that is your
problem, and I hope you get it fixed.

Posted by Christian Schatz (Member # 2961) on December 22, 2012, 01:51 PM:

Hello! I thank you all for your help. [Smile]

My updated test results (magnetic sound):

Monitor: good, clear sound & no dropouts
Aux out: distortion & dropouts
External speaker: distortion & dropouts
Internal speaker: distortion & dropouts

I looked on the electronic schematic for the ST-1200D M&O. If the amplifier were defective, monitor out would have the same issues like the other outputs (they
are serially connected: first is monitor, then some wiring and capacitors etc, and the leftover is on the special circuit in the backcover). I think i have to test the
capacitors and resistors after the monitor out.

But there are good news, too. After enough cleaning, alignment of the film guide and new greasing, the Elmo is playing all my reels smooth. No chatter anymore.
I still think i made a good deal. The Elmo comes with the 1.1 lens and i payed 84€ for it. [Big Grin]

Even if i cannot fix the internal speaker problem ... i use my
external stereo amp for better sound anyway.

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