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My Elmo ST-180E has a squeal when you turn the volume up loud. At middle level it is fine. The needle on the record meter peaks when this happens even though I'm just running a film, not recording. I have tried pushing in the record button over and over while the projector is in project, with no film of course, many times with no change. Holding down the record lever also. Cannot get it to stop. Anyone know a fix? Thanks
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Hi Tom,
This seems like a feedback problem. An audio amplifier magnifies the voltage that shows up at its input. If that output gets back to the input, you can get to the point where the output drives the input and you can get sound (not very pleasant sound) through the speaker even without an input. This is exactly what happens when a singer carries their microphone in front of their own speaker. Usually a tiny sample of the output is fed back in a way that reduces the output in order to prevent this, but when that fails anything goes.
I've seem this one twice.
The first time I had an ST-1200HD where on channel 2 when I turned the volume up it broke into a high pitched squeal. I came to the conclusion it was a real failure ("-now what?"). I knew a forum member had a schematic and he kindly sent it to me. I looked at the schematic for something that would only effect channel 2 and noticed a pre-amp IC there. I guessed it was this. I looked for the (obsolete) part and found it on e-Bay. I got 4 of them ("Replace 'em all!"). I have a gracious friend at work who has Ninja soldering skills and works at an industrial quality soldering station. I could have swapped them out at home, with what I have, but having him do it tipped the odds further in my favor. I brought the board home, installed it in the machine, took a deep breath and tried it out. It worked! By the time I was done with all this, I lost the machine a good six months!
The second time I found a new in box ST-800. It had been sitting in a photo shop since the 1970s waiting for a customer to just show up and bring it home: it was quite virginal. The problem is electrolytic capacitors need to be kept operating to stay capacitive. When I finally eased this thing up to the point where I dared plug it in, I got a low frequency buzzing tone on the audio over a certain volume setting. I guessed (hoped) maybe this was happening because my electrolytics weren't done re-forming up. I let the thing sit plugged in all day, and the volume level for feedback gradually rose higher and higher until the problem solved itself.
Your problem here could be the opposite: that your capacitors are actually on the way out because your machine has been in service.
There is always hope here: the Switch Trick. You unplug the machine and work audio switches maybe 10 times each. You also find appropriate plugs and work things like headphone and microphone jacks the same way. I can't promise this will help, but it's easy, quick and cheap and always worth trying.
I've had sound problems that at the end of day defied all troubleshooting. I found another machine that was dead for other reasons and swapped boards. I was very lucky once and found a machine that had shipping damage, but the guts were pretty low mileage.
Best of Luck! -
Wow. Great advise. I will work with the audio switches and see what happens. I thought of plugging into the headphone & mic jacks, but didn't try. Will do that talso. What are you thoughts on contact spray cleaner. The Radio Shack stuff? Risky? Thanks!Comment
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Other people swear by it, but I have no experience with it, so I really can’t say much one way or the other.Comment
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