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Has anybody else had problems with gr...

:: EPE Chat Zone ­:: ­Radio Bygones Message Board :: » EPE Forum Archives 2010 - » Archive through 25 December, 2013 » Has anybody else had problems with green plastic Omeg pots? « Previous Next »

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rainsbury
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Username: rainsbury

Post Number: 53
Registered: 01-2013

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Posted on Saturday, 30 November, 2013 - 02:45 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Has anybody else had problems with green plastic Omeg pots? I have had several fail recently and I am trying to find out why.

One of them is intermittent, it happens to be the coarse tuning on one of the voltage controlled oscillators of a synthesizer and the pitch jumps all over the place, especially if touch the knob or push it in slightly.

The other faults are generally only when I touch the knob, and again mainly noticeable if I slightly push it into the panel.

Is this a common issue?

Is it because I have been working on the panel face down and damaged the pots that are slightly higher that the others?

I have a new soldering iron that is temperature adjustable, do I have the temperature too high?

The one that completely failed had to be completely re-wired twice, could that have damaged it?

It looks fine and I can't see any obvious damage, so any suggestions would be welcome.
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cjay
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Username: cjay

Post Number: 16
Registered: 10-2013

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Posted on Sunday, 01 December, 2013 - 10:11 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Not specifically Omeg ones, I've had it in the past where there was enough movement in the shaft that it bent the wiper and made it intermittent.

I've also seen the backs of pots forced away from the body when the shaft has been pushed in and on others I've seen the tracks cracked from similar mistreatment.

The only way to find out what's going on is to do a thorough post mortem on one of the failed pots, magnifying glass and close examination.
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rainsbury
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Username: rainsbury

Post Number: 54
Registered: 01-2013

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Posted on Sunday, 01 December, 2013 - 12:03 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

cjay, thanks they are enclosed welded and riveted construction so dismantling them will probably destroy any evidence.
I posted the same request on another board and it seems that as they get older they become stiffer and then fail. Any on/out movement of the shaft damages the wiper and causes the fault I am having.
So that's 29 pots on one all going to be replaced, which will probably result in a total re-build, and the 36 I just bought from rapid will be going on e-bay.

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mark
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Username: mark

Post Number: 10
Registered: 09-2013

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Posted on Thursday, 12 December, 2013 - 01:54 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

The Omeg ones have been relatively good in my experience. Maybe something has changed. I have had several failures in the similar - usually blue - ones used in domestic dimmer switches. They are awful things with a push-on-push-off switch action as well as the rotation. with luck they last about a year. And why do simple dimmer switches cost between 6 and 20 pounds anyway, when a top brand double switched socket costs about 3.99. I don't get it - it's certainly not because of the quality of the pots.
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rainsbury
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Username: rainsbury

Post Number: 55
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Posted on Thursday, 12 December, 2013 - 04:46 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I think I have solved this one by taking a dead one apart. It was very slightly proud of the rest so when I was wiring the panel up, face down, the whole weight would have been on its shaft and I am 99% certain it simply pushed the wiper away from the track enough for it to become noisy.
This is on the main synthesizer that I use for live work so I can't afford for this to happen again and so I am replacing the whole lot with Alpha pots. It has taken 6 hours to replace about a third, but they are the most difficult ones to get to so I am hoping that I will be able to do the remainder in the same time.
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cjay
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Username: cjay

Post Number: 19
Registered: 10-2013

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Posted on Thursday, 12 December, 2013 - 05:55 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I'd imagine the fault could happen again with almost any make of pot, once replaced you need to remember to work on the panel while it's properly supported.

Being a little picky perhaps but it does seem slightly unfair to blame the particular make of pot now you've identified the cause of the failure.
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gordon
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Username: gordon

Post Number: 943
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Posted on Thursday, 12 December, 2013 - 07:24 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

That is useful information. I would never have guessed you could damage a pot in that way. I guess the metal can types are less prone to this damage, as the resistive track is at the front of the pot, when looking at the shaft.
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rainsbury
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Username: rainsbury

Post Number: 56
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Posted on Thursday, 12 December, 2013 - 10:28 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

cjay: I wasn't blaming it, just observing the cause and effect and hoping that it might avoid somebody else having the same problem. The "alpha" pots have a metal shaft, with a step in it that stops it getting pushed into the body.

gordon: I think most pots seem to have the track on the front face, but with everything else I have tried the end of the shaft is recessed into the back of the casing so it can't get pushed in.

Ironically I only used these for this project because everything is so tightly packed and I wanted something that was going to last a long time and be maintenance free so I wouldn't have to change one, and now I have had to strip it right back and change the lot. Doh!!

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