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 Post subject: Eico 249 VTVM, Erratic Meter
PostPosted: Jun Tue 27, 2006 3:28 am 
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Location: Sandwich, IL, USA
I have an Eico VTVM in the shop this week and I’ve got the meter movement out on the bench. Something strange is happening and before I did any damage I thought I’d ask for your opinions. It’s looking like it could be an out of balance condition but the movement doesn’t appear to have been opened or tampered with. It’s completely sealed all round and is clean inside, i.e. no dust, etc. It does respond to a voltage (through a 1m pot) when applied.

The problem is that the needle is pegged negative when the meter is held upright (vertical) and when turned upside down (180deg) moves up scale about 1/4 of the scale. The zero adjust screw is moving the fork and the fork is moving the needle when its laying flat (facing up) or upside down (upscale) but not enough to bring it of the peg when it is upright.
The front and rear springs look like they are still attached properly and coiled evenly. All the weights appear to be in their original position (no bright spots) on the counterbalance, none look like they have slipped. I treated the face with Staticide to eliminate that possibility.
Any ideas???
Denny Graham
Sandwich, IL


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 Post subject:
PostPosted: Jun Tue 27, 2006 3:41 am 
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Location: Westminster, CO, USA
Sounds like it's a balance issue to me. You can actually see the counterweight on the bottom end of the needle? I have a 232 sitting here and the needle stays pretty well put no matter how I tilt it around. I can see what looks like a few turns of wire and some solder on the tail of the needle (sticking below the pivot support).

When you say "pegged negative", do you mean with power on or off?

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 Post subject:
PostPosted: Jun Tue 27, 2006 9:11 am 
It's possible that one of the bearings has come loose. See if there is any play in the armature by gently wiggling it (you may need to use tweezers). If so, back off the front locknut and tighten the bearing setscrew slightly then retighten the locknut. I had this happen once on a meter movement. Don't know how it happened but it caused a similar problem to yours and tightening it cured it.
Also, it could be a case of fatigued hairsprings and requires rebalancing.
Rick Smith
San Diego, CA


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 Post subject:
PostPosted: Jun Tue 27, 2006 9:42 am 
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Location: Sandwich, IL, USA
The back of the meter is clear plastic Tony, you can see the whole meter movement. The balancing weights are little square brass tabs that are crimped onto the counterweight. Your needle response is what I would expect, no difference when tilted. No power-meter is completely out of the unit, laying by itself on the bench.
Rick, that seems like a good possibility, it’s about 3am, so after I get a little more snooze time, I’ll check that out.
Denny Graham
Sandwich, IL


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 Post subject:
PostPosted: Jun Tue 27, 2006 5:17 pm 
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Location: Des Moines,Iowa
Hi, I have a Eico 232 and if I hold it vertical upside down yes the needle will move off the center point but should stay on the zero in the upright position you can down load the manual I believe from Bama there is calibration procedures that may fix if that dont work you have a defective meter - Bob p.s think that requires a D battery and a couple of tubes there is an earlier post on static electricity affecting meter movement


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 Post subject:
PostPosted: Jun Tue 27, 2006 7:17 pm 
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Location: Sandwich, IL, USA
Nope Rick, that didn’t do it, going to have to look else where. The needle also seems to stick at the low end, yet it is free in the bearing through out the rest of the movement.
Seems to me there was a thread that addressed a sticking meter a while back but I can't remember nor find it now.
Bob, if you refer back to my earlier post you will see that I already addressed the static issue, first thing I looked at. Thanks but I downloaded the manual before I even opened up the unit. The calibration procedure refers to the Total calibration of the assembled unit, not problems with the individual components such as this is. I believe that the unit should be usable either in the vertical (facing you) or flat (facing up) position, I wouldn’t think that the needle should wonder around when turning to either of these positions.
Don't think I'm gonna get this one fixed, short of finding another movement.
Denny Graham
Sandwich, IL


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 Post subject:
PostPosted: Jun Tue 27, 2006 8:53 pm 
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Denny Graham wrote:
I believe that the unit should be usable either in the vertical (facing you) or flat (facing up) position, I wouldn’t think that the needle should wonder around when turning to either of these positions.

Hi Denny,

That's correct. A properly balanced meter movement will read 0 regardless of its position... vertical, horizontal, or vertical rotated any amount in either direction.

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 Post subject:
PostPosted: Jun Wed 28, 2006 1:09 am 
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Location: Oswego, NY, USA
If the needle sticks, it might be caused by a small speck of dirt or metal filing that's hiding out in the armature to magnet air gap (they can be difficult to see..a magnifying glass can help), or under one of the two jewel bearings (not as common). To clean out the air gap, use small cut strips of masking tape or Post-It paper, being careful to not touch either hairspring. Often, the scale must first be removed. To clean a bearing, apply a small drop of pure alcohol (ethanol or methanol) or residue-free electrical/switch cleaner, etc. to help wash away any particles under the bearing. Needles will sometimes stick to the left or right mechanical post stop if the stop post has been bent at the wrong angle. They can get bent if the meter was previously dropped. If the mechanical stop post is out of position, and allows the needle/armature to travel a little too far, that will also cause needle sticking in some models.

Fred


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 Post subject:
PostPosted: Jun Wed 28, 2006 11:46 pm 
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Results from messing round this afternoon. Nothing seemed to make a difference so far, so I’m back to what I first suspected, balance! First thing before I even posted was Staticide, then checked for flotsam in the gap, the unit is sealed quite nicely so I didn’t think I would find a problem there. Been messing with the bearings as Rick suggested but that’s not the problem either.
Even though the counter weights looked like they had not moved, I decided to try and move one and see just how tight they were on the cross. WOW! They moved very easily, which now makes me think that this was possibly jarred very hard at one time and they might have moved. Since the needle seems heavy in the upright position (moves negative) and also swings to the bottom when inverted it appeats that its not counterweighted enough. After sliding the weights out to the ends of the cross the needle seems much more stable and in balance. Problem now is figuring out the procedure to properly balance it. Besides the weight opposite the needle there are also weights off the cross pieces as you can see by the picture. Anyone have any experience with this?
Image

Denny Graham
Sandwich, IL


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 Post subject:
PostPosted: Jun Thu 29, 2006 2:16 am 
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Denny Graham wrote:
...Problem now is figuring out the procedure to properly balance it. Besides the weight opposite the needle there are also weights off the cross pieces as you can see by the picture.

Hi Denny,

Good progress, and a great photo :D

To balance:

Place the meter flat on its back, needle horizontal, coil pivots vertical. Set the front zero adjuster to mid-range, then set the needle to zero using the back adjuster. Make this adjustment as accurately as possible. Blow on the end of the needle a couple of times and make sure it settles back to zero from either direction.

Stand the meter up facing you and rotate it 45º left so the needle is horizontal, still pointing to scale 0. Move the adjuster at the right end of the needle (opposite the point) as required to zero the needle.

Rotate the meter 90º right, so the needle is vertical. Adjust one of the side adjusters to bring it to zero. Which one depends on the relative positions of all three. They should be roughly symmetrical about the axis of rotation.

When you're done the needle should stay on zero even if you roll the meter around like a tennis ball :D

A note regarding parallax:

Parallax is an error introduced when your line of sight is not absolutely perpendicular to the meter scale. Because the needle is distant from the scale by a small amount, it appears to point to a location on the scale different from the true location.

The proper correction for parallax error is a reflective ("mirrored") surface on the meter scale. You use only one eye for this method. Move your head so that the needle appears to bisect the pupil of that eye. Then look up to the needle point without moving your head, and take the reading.

This enhances the reading accuracy considerably. You can duplicate this method by taping a flat piece of aluminum foil to the meter face temporarily and use it to make your adjustments, then remove it.

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http://www.AtwaterKent.info
Click "Grebe Stuff" for Synchrophase info


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 Post subject:
PostPosted: Jul Sat 01, 2006 3:53 am 
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Well I finally got back to the meter to day. Leigh, thanks for the balancing lesson, the procedure makes complete sense the way you laid it out. And, I was getting it to balance pretty well, before the lightning bolt struck.
The needle had a slight bend about an inch from the tip and some white powder on it. You know how delicate they are, So I backed it up with a little piece of hard rubber and was going to use a foam q-tip to clean it and the minute I touched the needle the bent portion of the tip dropped on to the bench. After a couple of aw S&*T’s and a close examination I realized that the powder was oxidized Aluminum popping through the black paint. Many needles are made and mounted like this one. It is simply a piece of .025” aluminum tubing that has the portion over the scale flattened to present a narrower indicator. This one must have been in a damp area at one time and the aluminum needle corroded all the way through. Looking at it under a 10x loupe I could see white powdery spots all the way along the full length of the needle. I’m surprised the chassis wasn’t rusty.
So needless to say I was ready to junk the whole thing at this point. Then I noticed that the needle simply slips over the portion of the cross that attaches to the coil and that if I remove it and slip another .025” aluminum tube over it we’re back in business. I can flatten the end, a little flat black paint and good for another 40 years.
So what’s the problem now? Finding six inches of .025” thin wall aluminum tubing, that’s the problem. So if anyone has any suggestions, I’m open for ideas. I’m looking on hobby shop sites right now but all I’m finding is brass tubing in that small of a size.
Denny Graham
Sandwich, IL


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 Post subject:
PostPosted: Jul Sat 01, 2006 4:07 am 
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Denny Graham wrote:
Finding six inches of .025” thin wall aluminum tubing, that’s the problem. So if anyone has any suggestions, I’m open for ideas.

Hi Denny,

McMaster-Carr http://www.mcmaster.com has .025" (and .022" and .018") wall round tubing on page 124 of their catalog. Enter the page number in the search box at the upper left. And look around on adjacent pages. Might be other selections.

No minimum order, but you might find the available lengths to be more than you need. What's the OD? the .025" wall mentioned above is 1/8" OD.

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http://www.AtwaterKent.info
Click "Grebe Stuff" for Synchrophase info


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 Post subject:
PostPosted: Jul Sat 01, 2006 4:44 am 
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What you need is a 23 gauge aluminum hypodermic needle, the OD is .025.

Dave


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 Post subject:
PostPosted: Jul Sat 01, 2006 7:08 am 
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I have at least thirty pieces of test gear here, with built in meter movements and although most are well balanced when rotated to various positions while being held vertically,not even one of them retains perfect balance in both flat and vertical positions at all degress of the compass during rotation.

My reading and experience both lead me to believe that if I hold the meter vertically and rotate it to various positions while it is still vertical,I can realistically expect a deviation of about one or possibly two tiny scale division from absolute zero balance.

Anything better than that seems more theoretical than obtainable in actual practice,unless you own ultra costly lab grade gear,perhaps.I am not experienced at using the best quality lab gear.
Malcolm


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 Post subject:
PostPosted: Jul Sat 01, 2006 7:23 am 
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Location: Des Moines,Iowa
Have to agree with Malcolm on a slight variance in vertical and horizonal postitions of a meter and good to see Malcolm back on the forum :) Bob


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 Post subject:
PostPosted: Jul Sat 01, 2006 7:24 am 
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Hi Malcolm,

I expect your observations are correct.

These are production items, and manual adjustments cost money. They're made to meet a particular specification, which is not published, and if they meet it they go out the door. I'm sure none is perfectly adjusted when it's delivered.

As to the degree of precision required when repairing one, that's something for the owner to determine. Different people have different expectations. The sidearm adjustments affect the tracking of the meter. If they're not set accurately, the deflection will not be linear from 0 to FS.

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Click "Grebe Stuff" for Synchrophase info


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 Post subject:
PostPosted: Jul Sat 01, 2006 1:19 pm 
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Location: Rhode Island
Leigh wrote:
Hi Malcolm,

I expect your observations are correct.

These are production items, and manual adjustments cost money. They're made to meet a particular specification, which is not published, and if they meet it they go out the door. I'm sure none is perfectly adjusted when it's delivered.

As to the degree of precision required when repairing one, that's something for the owner to determine. Different people have different expectations. The sidearm adjustments affect the tracking of the meter. If they're not set accurately, the deflection will not be linear from 0 to FS.


Hi Leigh,
I know you own (or did own)a 249 yourself.Are you saying that the meter movement in this instrument has the inherent capability of allowing truly precise zero adjustment in both vertical and horizontal planes at all compass points?
I personally like the 249 because I am a kit instrument freak but its meter movement is certainly not top shelf stuff so I would not expect better than the one or two division discrepancy I mentioned previously.
Malcolm


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 Post subject:
PostPosted: Jul Sat 01, 2006 4:46 pm 
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Thanks Leigh, I never would have thought of McMaster, I buy a lot from them also. I use their will-call since they are only an hour away from me. I spent a good hour looking at Hobby Shop sites and Micro Mark because they have the telescoping tubing for model making. None that small though, 1/16” (.062”) is the smallest I’ve found.
I don’t think that that will help me if that’s the smallest size they list, .125”x 025”wall is a gigantic tube compared to the tube used for this needle. I would have to counter weight that with wheel weights. I’ll look see if they have anything smaller, this is for a meter needle remember, light as a feather. The O.D. is .025” its difficult to tell what the wall was because I don’t have a caliper that will go that small and don’t have access to a comparator anymore. My guess would be somewhere around a few thousands wall. Some kind of capillary tubing might work but again, usually not aluminum and usually not that thin of a wall.

Dave I thought hyp needles were stainless? Never saw an aluminum one and wouldn’t know where to begin to find one and besides, I would probably have to have a doctors prescription so he could get his cut. Although they would be about the right diameter. You tain’t a doctor by any chance, are ya Dave????

Again, good to see ya back Malcolm. Don’t misunderstand me, I’m not looking for an absolutely, perfect balanced needle, we never implied that. In fact I would agree with all said here about the meter in this unit. There will be a slight difference (a couple of scale units) on most service grade meters. Initially, I described the problem by explaining that the needle was pegged negative when laying on its back and moving a couple of inches positive when stood up vertical, (normal) that, is way out of balance, and way out of spec. And yes if you consider the lever moment of the side counter weights with the needle vertical, it gets very, very touchy if not imposable to get it in absolute, perfect balance. When we raced midgets the wide magnesium wheels had a very deep hub, almost at the back of the rim. Trying to balance them on a bubble balancer sometimes took an hour and just scraping a tiny bit off the surface of the wheel weight with a razor was enough to throw you off a full bubble. Made big differences at 130mph. Balancing the needle vertically presents the same mechanics.
Now back to Dave, really do you have any idea where to get a Aluminum hypo like you described or did you just find that on the net some where??
Would help a bunch to know someone that worked at a Meter factory. Would help a bunch to find a meter from a junker also!

Denny Graham
Sandwich, IL

Ps. Here’s another 1000 words if anyone cares to see it.
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 Post subject:
PostPosted: Jul Sun 02, 2006 12:22 am 
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Hi Denny,

I misread the earlier post. I thought the .025" dimension was the wall thickness rather than the OD. Sorry for the confusion. :oops:

Looks like your making progress. Good luck with it.

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 Post subject:
PostPosted: Jul Sun 02, 2006 9:56 am 
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Damn! A year ago,I could have sent you a whole 249 meter movement in near mint condition but that is gone now,Denny.
I will check my pile of disposable-meter-movement-for-parts collection but I don't think I have anything long enough.
Malcolm


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