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Old 3rd May 2019, 6:06 pm   #1
Diabolical Artificer
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Default Panel meter sticking - causes?

As it says in the thread title, I have a 1mA FSD 4" panel meter that's sticking at about half way and 3/4 FSD. I've had a look into the movement with a magnifying glass and blown it out with compressed air, no visible debree and no improvement. Also tried loosening the locating screw a tad.

What are the typical causes of sticking movements and any tricks to improve said fault? TFL, Andy.
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Old 3rd May 2019, 6:16 pm   #2
Malcolm G6ANZ
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Default Re: Panel meter sticking - causes?

Static on the glass?
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Old 3rd May 2019, 6:39 pm   #3
The Philpott
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Default Re: Panel meter sticking - causes?

Some of the troublesome (and tiny) pieces of ferrous debris i have encountered in these situations were blade shaped- and could only be seen if viewed at a favourable angle. I got into the habit of trying as many angles as possible to isolate and remove any potential troublemakers. Just a thought.

Dave
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Old 3rd May 2019, 7:44 pm   #4
Ian - G4JQT
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Default Re: Panel meter sticking - causes?

I have an Avo CT160 and the meter sticks because a tiny fake of glue (used to hold the glass in I think) gets stuck in the movement occasionally.

Ian
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Old 3rd May 2019, 10:05 pm   #5
'LIVEWIRE?'
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Default Re: Panel meter sticking - causes?

I have two by now quite old Radiomobile 1watt/10watt output meters, which I keep connected to my bench speakers (The meters have switches which allow either Meter only, attenuated speaker, and speaker only to be selected) The pointer on one of the two sticks at FSD if anything close to 10 watts is applied to it. This has been the case for many years. A slight tap on the metal case of the wattmeter is enough to free the pointer, and I've never been able to establish the cause.
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Old 4th May 2019, 8:17 am   #6
Diabolical Artificer
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Default Re: Panel meter sticking - causes?

"Static on the glass? " Didn't think of that one , I cleaned the glass inside and out with IPA at first, then as that didn't get 100% of smears off I used the old vinegar and newspaper, thios to two meters, one sticks, tother doesn't. I guess I could earth the glass to be certain.

It's hard to see inside the movement Dave though I thought I saw a bit of metal filling with one of those things a Dr uses to look into ears. Will check again. I tried to get in with some double sided tape but couldn't, what did you use to remove detritus?

Tapping the meter in this case isn't an option, will have to have another look.

Andy.
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Old 4th May 2019, 9:15 am   #7
The Philpott
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Default Re: Panel meter sticking - causes?

...shaped Blu-Tak pressed on and around the end of a cocktail stick (or on the end of a piece of solder if the access is convoluted) Solder will leave black marks on the scaleplate if you're not careful!

Blu-Tak becomes more sticky if it's worked by hand for a while- then it's very good for grabbing any offenders.

Dave
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Old 4th May 2019, 10:09 am   #8
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Default Re: Panel meter sticking - causes?

I have a Farnell bench supply and the panel meter has an acrylic bezel. If dusted with an ordinary duster the bezel gains a static charge, thus freezing the needle in some random position. The charge can persist for remarkably long periods, sometimes hours. The only instant solution I've discovered so far is a wipe with a damp cloth.

Alan
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Old 4th May 2019, 10:19 am   #9
The Philpott
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Default Re: Panel meter sticking - causes?

Sometimes steaming up by breathing on it is enough!
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Old 5th May 2019, 7:12 am   #10
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Default Re: Panel meter sticking - causes?

"..shaped Blu-Tak pressed on and around the end of a cocktail stick " Thanks Dave. My Daughter mixed some blutak with one of her lotion's/potion's trying to make silly putty as per a Utube video, the result was super blutak, it's very soft and sticky, I'll try that.

Will check the meter later for static. Andy.
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Old 5th May 2019, 7:27 am   #11
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Default Re: Panel meter sticking - causes?

Hi,

I have seen an interesting mechanism for this problem.

I had a similar problem in a meter in a Sailor radio. I did the same sort of thing checking it, but it was initially hard to see that there were pieces of debris in the path of the rotating coil.

Sometimes the pole-pieces which are made of laminations, the electroplating fails. A rust crystal grows out of the surface, or other particulate matter there jams or partially jams the rotating coil.

If it is that, extracting it is a challenge. I found a way, sliding thin sections of Kapton (polyamide tape) in there to grab the particulate matter on the tape glue and extract it. You cannot wash it out with cleaner.
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