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 Post subject: Panel Meter Restoration/Rebuild
PostPosted: Dec Sun 25, 2011 5:49 am 
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Joined: Aug Mon 23, 2010 3:30 pm
Posts: 66
Location: Canada
I just recently acquired two Eico testers, neither one in operating condition. The 666 has in bad shape electronically and I think I have it restored (correct resistors and caps & clean solder joints) but the meter needle doesn't move freely and gets caught while moving.

The 667 meter doesn't move at all.

Is there a simple procedure for fixing & restoring a old panel meter?

Thanks!


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 Post subject: Re: Panel Meter Restoration/Rebuild
PostPosted: Dec Sun 25, 2011 11:48 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 16749
Location: Albuquerque, NM 87123
Simple? No.

There can be several reasons for a needle to hang up, but all the repairs involve taking the meter housing apart. It could be paint flakes or metal shavings around the coil, a bent needle, damaged or dirty pivot, etc.

If you are not familiar with meter repairs you can do more damage; they are delicate.


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 Post subject: Re: Panel Meter Restoration/Rebuild
PostPosted: Dec Sun 25, 2011 3:39 pm 
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Joined: Aug Mon 23, 2010 3:30 pm
Posts: 66
Location: Canada
Yes, I do understand that that these are very delicate things.
Are there any things that I should NOT do?
Are there any parts that I should lubricate or clean with contact cleaner?
Does blowing compressed air sound like a good idea?


Last edited by jcmjmp on Dec Sun 25, 2011 3:43 pm, edited 1 time in total.

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 Post subject: Re: Panel Meter Restoration/Rebuild
PostPosted: Dec Sun 25, 2011 3:40 pm 
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Joined: Aug Mon 23, 2010 3:30 pm
Posts: 66
Location: Canada
Double post.


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 Post subject: Re: Panel Meter Restoration/Rebuild
PostPosted: Dec Sun 25, 2011 3:49 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 25381
Location: Pocasset, Cape Cod, MA
Most likely there are flakes of metal oxide in the magnet gap. Remove them with slivers of masking tape worked around in the gap with nonmagnetic tools. You definitely don't want to use compressed air around the hairsprings. You'll need very good close-up eyesight, or a binocular microscope. The pivots don't need (and shouldn't have) lubrication.


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 Post subject: Re: Panel Meter Restoration/Rebuild
PostPosted: Dec Sun 25, 2011 4:27 pm 
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Location: Long Island NY
First, there are people on this forum who do meter repairs, and you'll probably hear from them at some point. If you are not familiar with meter repairs, you might be better off having somebody who has the know-how help you out.

Do not ever spray any kind of lubricant, contact cleaner, or other solution into a meter movement. They are meant to run dry. Anything that gets in there is only going to make matters worse.

If you want to go further, look at the meters closely. On nearly all old ones, and high quality instruments of later manufacture, the movement is assembled with tiny screws. It is possible to disassemble and repair them, but it is not easy unless you are familiar with such work and have a good assortment of jewelers' tools. But starting in the mid-1950s, some meter companies switched to "modular" designs, where the inner parts were cast and molded together on automated machinery. Such meters were not made to be taken apart or repaired, so if that's what you've got, you may not be able to go much further.

There are a few reasons why a meter will stick at certain places along the scale. One is because the pointer is too low, and is dragging on the scale, or perhaps too high, and hitting the clear plastic or glass cover. First look to see if there is a reason why: is the scale loose or not fastened properly? Is the case or frame to which the other parts are attached bent or distorted? If you have to, bend the pointer ever so slightly from the coil end as needed until it clears. Don't try to bend from the pointer end. The pointer is an extremely thin piece of aluminum tubing which tapers towards the pointer, and if you try to bend from the pointer end, it may kink or break somewhere in the middle.

Another reason is because dust or debris has gotten between the armature and the magnetic poles. A strong light and a magnifying glass are needed here. If the debris are non-ferrous, a little low pressure air from a can of "dust remover" should do the trick. Take care not to blow on the coiled hair springs at either end of the armature; they are very delicate, and a blast of air can mangle them. Ferrous debris will stick to the magnet and resist being blown out, so a small piece of adhesive tape might be used to "fish" them out. Some people use a feather for the purpose, but it's not easy to find one that will fit in the tiny spaces of a panel meter movement.

If the first two steps have not resolved the problem, you have to consider that the pivots may be too tight or damaged. Some meters have pot metal components which expand with age, putting pressure on the pivots and causing them to bind. Sometimes it is the result of previous mis-adjustment. Panel meter pivots are meant to have a tiny bit of play (about 0.003"). Due to their conical shape, this can be ascertained by pressing on the side of the coil with a suitable tool to see if it has a tiny bit "side shake." If not, you can loosen the locking nut and turn the jewel holder out perhaps 1/8 of a turn at a time to see if it helps. Don't ever tighten a jewel holder up on a pivot, as this can distort the end and cause real grief.

If the meter has been dropped or subject to severe shock or vibration, the pivots may be damaged, or one of the jewels may be cracked (on most panel meters, the "jewels" are made of glass, not semi-precious stones!) It is possible to recondition a deformed pivot, but it calls for complete disassembly of the movement. A replacement jewel, if needed, would have to be taken from a junker meter.

As for the meter that is completely stuck, the same general remarks apply.

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 Post subject: Re: Panel Meter Restoration/Rebuild
PostPosted: Dec Sun 25, 2011 6:40 pm 
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Joined: Oct Sun 15, 2006 12:57 pm
Posts: 7431
Location: Liberty, Missouri
There have been several posts on this subject over the last few years, and a search would give you a lot more of the same basic advise given here, all or any of which may be your culprit. In addition to the type movements Chris mentioned, "TauT" band movements are also essentially un-repairable outside the meter shop. They are easily identified by the lack of jewel pivots and the typical coiled springs.

I'm certainly not an expert by any means, however, of the dozen or so meters I've successfully resurrected over the years, far and away the most common problem was the loose magnetic or other particles in the gap where the coil moves, next was deteriorating paint on the dial face or damaged pointers.

Tools NEED to be non-magnetic. Stainless, very slender tweezers are the most helpful. The masking or cellophane tape trick is VERY helpful.

I highly recommend a thick plush bath towel or better yet a small feather pillow covered with a couple paper towels to work over, because when you're holding that meter movement in your hot little hand, you're in sudden death territory.

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 Post subject: Re: Panel Meter Restoration/Rebuild
PostPosted: Dec Mon 26, 2011 3:34 pm 
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Joined: Aug Mon 23, 2010 3:30 pm
Posts: 66
Location: Canada
Thanks, guys. That's really helpful. I'll try some of this today.
I'm worried about the non-magnetic part though. I just have regular tools.


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 Post subject: Re: Panel Meter Restoration/Rebuild
PostPosted: Dec Mon 26, 2011 5:31 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 25381
Location: Pocasset, Cape Cod, MA
Toothpicks.


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 Post subject: Re: Panel Meter Restoration/Rebuild
PostPosted: Dec Mon 26, 2011 10:29 pm 
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Joined: Aug Mon 23, 2010 3:30 pm
Posts: 66
Location: Canada
Well, turns out there wasn't much wrong with either one of the panel meters.

The 666 meter had a piece of double sided tape inside the housing that came undone and it was obstructing the needle's movement.
The 667 meter just needed to have a bit of air blown into it. 8)

I still need a 43Ω resistor for the 666 tester before I can calibrate it.
The 667 tester seems to be missing voltage in a couple of spots. I hope its nothing too serious and doesn't take me forever to figure out :(


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 Post subject: Re: Panel Meter Restoration/Rebuild
PostPosted: Dec Mon 26, 2011 10:45 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 16749
Location: Albuquerque, NM 87123
If you don't have a 43 ohm resistor you can use a 33 and a 10 ohm, or even two 22 ohm would be close enough.


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 Post subject: Re: Panel Meter Restoration/Rebuild
PostPosted: Dec Tue 27, 2011 2:40 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1982
Location: Oswego, NY, USA
Whenever you have a panel meter apart for this type of servicing; after you've repaired it and the needle responds well, it's a good idea to check its balance, which has been discussed often in the past on this forum. If the needle stays put, pretty much, at "zero" as you place the meter in various different orientations (to the earth), then balance is good and you are done. But if the needle veers alot off zero as you put the meter into different orientations (say, more than one minor unit/graticule or around 2 percent of full scale) then it's a good idea to balance it by either carefully moving one or more of the small counterweights, but often on older meters it's difficult to get these little weights to move, so it's OK to make some very small counterweights on the posts using droplets of glue or epoxy..I use Sobo glue. A balanced meter movement assures accuracy regardless which orientation you place the tester in.


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 Post subject: Re: Panel Meter Restoration/Rebuild
PostPosted: Dec Tue 27, 2011 3:13 am 
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Joined: Sep Tue 30, 2008 8:30 pm
Posts: 164
Location: Bay Village, OH 44140
As an experienced meter repairman, I am very glad to see others on this list
giving such complete & correct advice.
The only problem you all missed is static on cover glass which can cause
the pointer to stick.
There is antistatic fluid available (since I have a small bottle purchased
30 years ago) I do not know where to get it now.
However If you make a small weak ordinary soap solution & wipe it
inside & outside of the cover glass, wipe it mostly dry, let it dry & then
breath on it closely till it clears, you will remove static problem for a long
while.
Good luck


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 Post subject: Re: Panel Meter Restoration/Rebuild
PostPosted: Dec Tue 27, 2011 3:59 pm 
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Joined: Aug Mon 23, 2010 3:30 pm
Posts: 66
Location: Canada
Fred Scoles wrote:
But if the needle veers alot off zero as you put the meter into different orientations (say, more than one minor unit/graticule or around 2 percent of full scale) then it's a good idea to balance it by either carefully moving one or more of the small counterweights, but often on older meters it's difficult to get these little weights to move, so it's OK to make some very small counterweights on the posts using droplets of glue or epoxy..I use Sobo glue. A balanced meter movement assures accuracy regardless which orientation you place the tester in.


The older "666" panel meter does seem to be a little off in this respect. Where are these little counterweights? A picture would be great!


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 Post subject: Re: Panel Meter Restoration/Rebuild
PostPosted: Dec Tue 27, 2011 9:19 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 25381
Location: Pocasset, Cape Cod, MA
Opposite the pointer, in line with it but on the other side of the pivot. There may be two more at right angles, next to the pivot, for side-to-side balance.


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 Post subject: Re: Panel Meter Restoration/Rebuild
PostPosted: Dec Tue 27, 2011 10:34 pm 
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Location: Milford, PA
Since the subject of panel meters is on the table, I just want everyone's two cents about balancing meter movements. I see that a couple of you have already addressed this. I'm no expert, so be patient with me . I picked up an RCA WV98C vtvm recently for cheap. When I tried it out, it seemed inaccurate. Upon further investigation, I saw that when lying flat, it zeroed quite differently from when it was standing straight up. I looked closer, and two of the weights for the movement had fallen off! The one opposite the needle was soldered on and was fine, but the side balance ones just slide on,and had come off. I took the meter apart, and with much patience, put them back on with tiny needle-nose pliers, and slid them up and down the balance points until when lying the meter down or up only made one half of an increment of movement. After reassembling it and calibrating, it seems to work fine now. Is there any good info around about meter movement balancing?
thanks

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 Post subject: Re: Panel Meter Restoration/Rebuild
PostPosted: Dec Wed 28, 2011 12:19 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 25381
Location: Pocasset, Cape Cod, MA
It's been described here, six months or a year ago. Basically it's like balancing a see-saw. You hold the meter with the face vertical and the pointer horizontal, and the pointer should balance. You do that, and then hold it with the face vertical and the pointer vertical, and it should point straight up. If not you adjust the side weights until it does. That's probably going to affect the horizontal balance, so you repeat the steps until both are good.

Neither of these adjustments should affect the meter zero when the face is horizontal. That's what the two hairsprings do (besides carrying current to the moving coil).


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 Post subject: Re: Panel Meter Restoration/Rebuild
PostPosted: Dec Wed 28, 2011 4:25 am 
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Joined: Jun Fri 19, 2009 6:34 pm
Posts: 10243
Location: Long Island NY
After an exhaustive search, I am prepared to say that perhaps no more than half a dozen books have ever been published in English on the topic of meter repair. One of the best and easiest to find is, "Maintenance and Servicing of Electrical Instruments" by James Spencer. The third edition (1951) is the largest and most complete. It was published by The Instruments Publishing Co., Pittsburgh, PA.

Spencer devotes about a page and a half to the topic of balancing, and doesn't have a whole lot more to say about it than what has been posted in this thread and previous ones already. Several points worth noting, however, are:

1. Start off by zeroing the pointer with the face horizontal. Then bring the face vertical and rotate whole the meter counter-clockwise until the pointer is horizontal (i.e. pointing in the 9 o'clock position). It should still be at zero on the scale. If not, adjust the tail weight (opposite the pointer) until it is.

2. Rotate the meter clockwise until the pointer is vertical (pointing at 12 o'clock). It should still be at zero on the scale. If not, adjust the side weights as needed. You should move the weight out on the side that corresponds to the direction you want the pointer to go.

3. Rotate the meter to the vertical operating position (scale is level). If the pointer is not at zero, you may have to re-adjust the tail weight slightly.

4. The coiled wire weights found on a great many smaller panel meters are actually curved along their weight so they grip the balance arms. The right way to move them is to squeeze them gently along their entire length with a flat tweezer so the grip is released. If this is not observed, you may stretch or compress the weight, and it will try to return to its original shape over time, throwing the meter out of balance again in so doing.

5. Don't cement or glue the weights to the balance arms after you're finished, or somebody will be in for a very difficult time if adjustment is needed in the future.

Two observations: (A) If the meter is used in something like a tube tester, which is designed to be used in a horizontal position, one would be well advised not to do the balance adjustment. If the meter is used horizontally, the settings of the balance weights will not matter, and it's not worth the risk of breaking something to try balancing it. Meters that are intended to be used vertically, like the RCA VTVM, must be balanced or calibration will suffer.

(B) Some very large panel meters, i.e. those with 4" or 5" scales, simply cannot be brought into balance no matter what you do. If that's the case, try to balance the meter as well as possible.

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"Hell, there are no rules here--we're trying to accomplish something!"

Thomas A. Edison


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 Post subject: Re: Panel Meter Restoration/Rebuild
PostPosted: Dec Wed 28, 2011 12:47 pm 
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Location: Sarasota FL USA
The following thread is a good addition to this topic:

http://www.antiqueradios.com/forums/vie ... p?t=157995

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Sarasota FL
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 Post subject: Re: Panel Meter Restoration/Rebuild
PostPosted: Dec Thu 29, 2011 3:28 pm 
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Joined: Aug Mon 23, 2010 3:30 pm
Posts: 66
Location: Canada
I the needle doesn't always return to 0 like it should, does that mean that I need more weight on the tip of the counter balance or more weight towards the pivot point?


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