I just picked up this meter today at a flea market. At the time of purchase I noted that the two tiny screws that held the dial plate to the movement had come loose and were floating around the meter dial. The dial plate however was secure. I also noted that mechanical zero was the same whether the meter was standind up or laying down. So I took a chance on it and it turns out except for a bit of old battery corrosion, it seemed to work great. When I got it home I removed the clear plastic cover and then the dial to make sure I retrieved the tiny screws and any washers that may have come off as well. While securing the dial back to the meter my small screwdriver slipped at about the 2 oclock position and.went in and hit the magnet. It didn't seem to damage anything. After everything was re assembled I tweaked mechanical zero with the unit in the vertical position and took a known voltage reading with it. The reading after the accident read the same as before. It was then that I laid the meter on its back and noticed that now mechanical zero drifts abot.250 inch downward. Raising it back up to vertical put the needle back to zero. I know that I must have done this because it was fine before I slipped. I know that the tiny counter weight springs which are located at 9, 3, and 6 oclock have something to do with this delicate balance and I would like to try to adjust them but I don't know what the procedure is for making this adjustment so I don't want to make things worse or destroy the movement completely. Can anyone familiar with adjusting these movements please advise me on this? Thanks, Lenny
If it's vertical, the bottom needs to balance the moment arm of the needle.
With the needle moving downward (to the left), it means the needle is heavy relative to the counterbalance.
But I doubt the screwdriver incident did this unless it knocked one of the weights and bent the pin it was on.
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You are correct in saying that the balance of the movement is delicate. The tail weights are critical to the accuracy of your meter. There are three weights on the bottom (tail) of the meter pointer; the tail weight (on the bottom of the shaft of the pointer) and two side weights (on the cross-bar). I used to service these meters while working at a commercial cal lab in the late 60s. The procedure for balancing a movement is thus: (1) Center the mechanical zero tang so that it is in the middle of its range. (2) Position the meter so that the pointer is level horizontally. Adjust the tail weight so that the pointer rests on the zero mark on the scale (3) Position the meter so that the pointer is vertical. Adjust the side weights so that the pointer rests on the zero mark on the scale. (4) Position the meter so that it sits upright on the bench (pointer is at
45 deg). If the pointer doesn't come to exactly zero scale, more adjustment is needed. (5) Repeat steps 3 & 4 until the pointer is at zero in all positions.
You'll find that balance will be easier if you leave the tail weight alone after the initial balance (Step 1) and use the side weights to do the final trimming adjustments. You'll have to move the side weights inward or outward in unison to maintain the vertical balance. Make the adjustments in very small increments.
Keep in mind the principles of balancing a lever on a fulcrum; the heavier end will move down. The pointer's pivot is the fulcrum. The most difficult part of the procedure is to make the pointer balance when the instrument is upright on the bench. If the pointer is below the scale zero, then the side weights need to be moved out.
Hth,
--
"In theory, there isn\'t any difference between theory and practice. In
practice, there is." - Yogi Berra
Dave M
masondg44 at comcast dot net
This is a bit confusing. Do you mean that the pivot is also horizontal, or that the entire meter is on its back? If the meter is on its back, then the zero position is determined entirely by the mechanical zero adjusting the hair spring. The weights should have no effect.
If you mean pivot is horizontal with the needle also horizontal, tt seems like there is a step missing:
(1a) With the meter on its back, adjust the rear mechanical zero so that the needle rests on the zero mark.
This is exactly what's being done, thus the confusion. :)
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I wanted to update this message and also perhaps clarify a few things. It now seems that mechanical zero on the left side is pretty close to being the same both in vertical and horizontal position. I don't know what caused this to change but it apparently did. However now when zeroing the pointer on ohms to the right, in vertical position, as you normally would, I set the pot to deflect the pointer to right zero. Leaving the input shorted, I then turned the meter horizontal and noted that the needle moved about .250 inch to the right. It would appear that this is a more serious problem now . In the former scenario in my first post, though a pain in the ass, mechanical zero could be tweaked each time, depending upon the operating position of the instrument. However in this case, accuracy is definitly seems like it would be affected. I never considered the possibility of a "right side" problem. In addition, these spring weights are very tight and almost impossible to move. Perhaps my slip up didn't cause this deflection problem in the first place. I never looked at this aspect of operation. In any case though I don't know what to do about this. I also have a question: In step two, with the meter horizontal you said to adjust the tail weight so that indication is zero. As Sam has previously mentioned, in horizontal position, why would any weights affect the pointer's position? Lenny.
Just another note here. When I say "vertical position" I mean the instrument is standing up on the bench. In "horizontal position" the meter is on its back. Sorry for the confusion. Lenny
No.. the meter is not on its back; rather, stand it on the bottom left corner. The instrument should be held in front of you so that you are looking squarely at it. The meter should be positioned so that the pointer is level horizontally, and pointing to your left.
Please view in a fixed-width font such as Courier.
Dave I don't mean to be a pain but I'm trying to understand your last post. I think I understand what you've written but I'm not so sure about the drawing though. From what you said, I position the meter standing up in front of me. I then rotate the entire instrument 45 degrees to the left. The needle is now horizontal. At this point I adjust mechanical zero. Then I stand the meter back up (rotate instrument 45 degrees to the right) to see if zero is still the same? Well I did that and mechanical zero moves downscale,(left) when the meter is stood back up. Now to fix this am I correct to assume that the right side weight would have to be moved out slightly? And if I were to do this could it affect anything else? Or am I misconstuing the theory of the procedure? Lenny.
Here is how I've interpreted and edited what has been written:
Center the front mechanical zero tang so that it is in the middle of its range.
With the meter flat on its back (pivot axis vertical), adjust the rear mechanical zero tang so that the needle rests on the zero mark.
If easy access to the rear adjustment is not possible, simply adjust the front mechanical zero tang so the needle rests on the zero mark.
Since the pivot axis is vertical, only the mechanical (hair spring) adjustments matter.
Position the meter so that the pointer is level horizontally. To clarify, this means the pivot axis is horizontal and the entire meter is oriented at about 45 degrees (on most meters) with the needle pointing to the left horizontally. Adjust the tail weight so that the pointer rests on the zero mark on the scale.
Only the mechanical zero (performed in steps 1 and 2) and balance between the needle and tail weight matter.
Position the meter so that the pointer is vertical. Adjust the side weights so that the pointer rests on the zero mark on the scale.
(Only the mechanical zero (performed in steps 1 and 2) and balance between the two side weights matter.)
Position the meter so that it sits upright on the bench (pivot axis is horizontal, pointer is at 45 degrees). If the pointer doesn't come to exactly zero scale, more adjustment is needed.
Repeat steps (4) and (5) until the pointer is at zero in all positions.
As has been said, think about what you're trying to do - balance a rotating mass.
Suggestions/improvement welcome.
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It's pretty normal for a meter to read a little differently between horizontal & vertical. Touching the magnet shouldn't cause any problems.
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Well I made the adjustments as both Sam and Dave suggested. I want to thank both of you guys for all the advice. I could never have done this without your help. It was very difficult, but now balance in all planes is very close. In fact its as close if not better than my bench VOM. During the course of the procedure one side spring became so distorted that it was useless, and the other simply launched itself while I was holding it with the hemostat. Luckily I have a box of junk
260's and was able to scrounge two springs from an old movement. I'm glad that I learned how to do this but I don't want to have to do it again. You can easily destroy a movement with one careless.slip. Now that the mechanical is resolved I have to deal with an electrical problem. All AC ranges are inoperative. I found one resistor which was burned beyond recognition and was open but I have no schematic so I cannot troubleshoot this instrument. I also found out that Triplett was sold two years ago ironically to Jewell Instruments, a company here in New Hampshire. I called them today but they have little if nothing to do with older equipment. No schematics either. Does anyone know where I might be able to find a manual for a model
630APL? . .Thanks, Lenny
Assuming that only the one resistor is bad, estimate a replacement based on the ohms/V rating of the meter. Start high and work down if there is any response. If nothing else is smoked, you should be able to figure it out. Real engineers don't need !@$# schematics! :)
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Don't know how close it is to the 630APL, but it's a good bet that most of it is the same. You can buy a copy of the manual from the following sources:
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Cheers!!
--
"In theory, there isn\'t any difference between theory and practice. In
practice, there is." - Yogi Berra
Dave M
masondg44 at comcast dot net
has manuals for the Triplett
630A, 630NA, and the 630PL models for free download. From what I remebr about triplett, a lot of models used the same sets of resistors, so they might be close ebnough to find what you need. If it is in the divider, the values repeat, and incriment X10 each time. The Tripplet meters had a couple reistors that were common failures when someone got careless.
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They are in Deja format, but there is a free viewer program if you can't open them.
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I still have some 1% resistors left from my shop.
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Check the rectifier. If it got through the resistor, but DC ranges work, that would be next in line.
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I checked the meter diodes and they were both shorted. They were some obscure number that wasn't listed anywhere. So I pulled two out of an old junk 260 that was of a similar vintage. I don't know if the originals were silicon or germanium, if it matters but AC came right up and the accuracy as compared to my digital was not too bad at all. So my 1.00 flea market find needed a movement balance adjustment, it had two burned resistors, for which I did find the values, and two rectifiers for the AC. Someone really beat the shit out of this thing but now that its repaired its actually pretty accurate. For the 30V battery, I used four 6.50 V small lithium military surplus batteries. Each battery is half the size of an aa battery. I soldered them together and fit them inside the case. This was a nice little project. Thanks again everyone. Lenny.
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