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 Post subject: How to dismantle a sealed apm?
PostPosted: Jan Thu 12, 2017 4:40 pm 
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I want to modify an apm faceplate print, please help.
The apm is a Weston model 2531 50uAdc 3.5in diameter sealed unit. I got the bezel off, however, I do not know how to proceed further to unseal it.


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 Post subject: Re: How to dismantle a sealed apm?
PostPosted: Jan Thu 12, 2017 5:28 pm 
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What does the back look like?

What is an "apm"?

Meter movements are not normally removed from the front, but yours may be a "sealed" unit.

Does it look like this from the back?
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Curtis Eickerman

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 Post subject: Re: How to dismantle a sealed apm?
PostPosted: Jan Thu 12, 2017 5:55 pm 
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the back ...


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 Post subject: Re: How to dismantle a sealed apm?
PostPosted: Jan Thu 12, 2017 6:41 pm 
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Yep, sealed.

I've not taken one apart so you may get to a point where something is glued, but I hope not.

Next step is to remove the nuts from the terminals. You may then be able to remove the washers and plastic or neoprene insulators, but perhaps not. In any event, you are going to have to apply pressure to the terminals to push the unit out the front. Do not try to pry from the front.

With careful pressure and wiggling it should eventually separate from the metal housing.

You could stand it on the terminals while pushing down on the metal case to achieve the pressure needed.

What I don't know is whether there will be some additional disassembly after you get it free from the metal case.

I would not be surprised to find another set of nuts or bolts that have to be removed to extract the movement from the rest of the case. Ultimately the movement itself still comes out of the back of the internal case.

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 Post subject: Re: How to dismantle a sealed apm?
PostPosted: Jan Thu 12, 2017 6:50 pm 
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What's an apm?

- Leigh

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 Post subject: Re: How to dismantle a sealed apm?
PostPosted: Jan Thu 12, 2017 7:19 pm 
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analogue panel meter

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 Post subject: Re: How to dismantle a sealed apm?
PostPosted: Jan Thu 12, 2017 7:52 pm 
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Never seen that acronym before... Thanks for clarifying. It obviously would never have been used historically, because during the time that these meters were in common use, there weren't any other kinds of meters besides analog. So it has to be a fairly recent term.

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 Post subject: Re: How to dismantle a sealed apm?
PostPosted: Jan Thu 12, 2017 8:36 pm 
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Another useless, unneeded acronym has been invented.

Dave


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 Post subject: Re: How to dismantle a sealed apm?
PostPosted: Jan Thu 12, 2017 8:53 pm 
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Argh, how about a 50ua that can be disassembled?

Chas

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 Post subject: Re: How to dismantle a sealed apm?
PostPosted: Jan Thu 12, 2017 8:58 pm 
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Tom Albrecht wrote:
Never seen that acronym before...
Hmmm

It seems Tom and I agree.

Newcomers often invent acronyms thinking it makes them appear experienced and knowledgeable.
In fact just the opposite is true.

- Leigh

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 Post subject: Re: How to dismantle a sealed apm?
PostPosted: Jan Thu 12, 2017 10:01 pm 
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Usually when a military grade meter says "sealed," they mean it. Even if you manage to get it apart without destroying it, getting it back together again will present additional challenges.

Yours looks like it has some kind of epoxy or elastomer seal holding the glass to the case, so I'd see if epoxy remover (available at the local home center) will loosen it. Older meters of this type were sealed with solder, and required even heating all around. This was best done by chucking the meter in a lathe and spinning it fast enough that the heat from a propane torch was evenly distributed until the solder melted out. The hot glass would then fall off and break unless you were prepared with a rag or oven glove to catch it with. You may find a similar approach with a heat gun helpful to soften the glue or sealant if the epoxy remover doesn't work.

It should be pointed out that just about any non-sealed, bakelite case panel meter can be taken out of its case by simply removing a few screws, so it might be worth looking for one of those instead, and putting this sealed meter back on the shelf until you can use it as it is.

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 Post subject: Re: How to dismantle a sealed apm?
PostPosted: Jan Thu 12, 2017 11:04 pm 
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Ah. APM = analog panel meter.

Which I tend to call a "meter."

=)


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 Post subject: Re: How to dismantle a sealed apm?
PostPosted: Jan Fri 13, 2017 3:22 am 
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Use a very thin & sharp knife or single-edged razor blade.

Press in between the case and glass to break the seal. Do not 'cut' or pry.

Usually a few spots around the periphery and the glass will be free.

Then remove the nuts on the back to free the movement.

A lot easier than the solder-sealed jobs...

Let me know if you ruin something, I have lots of panel meter parts.

DDG

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 Post subject: Re: How to dismantle a sealed apm?
PostPosted: Jan Fri 13, 2017 4:45 am 
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Leigh wrote:
Tom Albrecht wrote:
Never seen that acronym before...
Hmmm

It seems Tom and I agree.

Newcomers often invent acronyms thinking it makes them appear experienced and knowledgeable.
In fact just the opposite is true.

- Leigh


I still choke whenever I see SMD used for Silver Mica Disease. A few week's back was GDO
being used for something other than a "dipper." Garage door opener as I recall. Confusing
to us old timers.

Pete

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 Post subject: Re: How to dismantle a sealed apm?
PostPosted: Jan Fri 13, 2017 8:01 am 
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Location: Toronto, Ontario, Canada
Thanks to Curtis, followed your instructions I got the "sealed - do not open ruggedized" meter taken apart nicely.

The truly sealed meter like the Hickok TV-7's requires the torch approach, I have seen that on the net but I don't think I have the courage to try that out myself.

I have been doing a fair amount of analogue meter searching on the net and must have gotten that "apm" virus somewhere.

Thanks everyone!


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 Post subject: Re: How to dismantle a sealed apm?
PostPosted: Jan Fri 13, 2017 1:46 pm 
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Congratulations. Nicely done.

Just wondering what the purpose is for converting the scale?

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 Post subject: Re: How to dismantle a sealed apm?
PostPosted: Jan Fri 13, 2017 2:11 pm 
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I want to convert this from 50uA to 200uA, have to add a shunt around 370 ohms to the original 1110 ohms coil and add another external series resistor to make 2365 ohm for TV-7 requirement.


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 Post subject: Re: How to dismantle a sealed apm?
PostPosted: Jan Sat 14, 2017 9:56 am 
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Peter Bertini wrote:
Leigh wrote:
Tom Albrecht wrote:
Never seen that acronym before...
Hmmm

It seems Tom and I agree.

Newcomers often invent acronyms thinking it makes them appear experienced and knowledgeable.
In fact just the opposite is true.

- Leigh


I still choke whenever I see SMD used for Silver Mica Disease. A few week's back was GDO
being used for something other than a "dipper." Garage door opener as I recall. Confusing
to us old timers.

Pete


Heck, GDO to me is GPS Disciplined Oscillator. We obviously need context to correctly identify abbreviations and acronyms.

-Pat

Edit to add - when I first read the thread title, I figured it was a typo of amp, and that it was a sealed amplifier.

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 Post subject: Re: How to dismantle a sealed apm?
PostPosted: Jan Sat 14, 2017 6:58 pm 
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Peter Bertini wrote:

I still choke whenever I see SMD used for Silver Mica Disease. A few week's back was GDO
being used for something other than a "dipper." Garage door opener as I recall. Confusing
to us old timers.

Pete


GDO has always been used for Garage Door Opener as far back as I can recall by those of us in the retail and service industries, in fact I have never heard of it being used for anything else. I trashed a bunch of old training material from the 70's several years back that referred to the units as GDO's.

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 Post subject: Re: How to dismantle a sealed apm?
PostPosted: Jan Sat 14, 2017 7:56 pm 
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SMD is Surface Mounted Device in the semiconductor industry.

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