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Hi,
Repairing this tube tester for a customer. The meter is stuck on "12", should be zero with no power applied. The mechanical zero adjustment does nothing.
What are my options and any caveats trying to correct this? Thanks,
Richard
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Well, is it stuck due to something holding it? In any case you will have to open the meter and inspect the movement. Usually the adjustment is done using a small spiral spring with one end attached to the galvanometer's coil and the other held by some thingy with a bump which goes through an oval slit ina lever rotated by your adjustment knob. The result is the spring tension varied and the spring pulling on the coil setting zero position. You have to see if there is an obstruction.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
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Test the movement for continuity. Most have full swing at about 50ma. If the winding is continuous, look for an obstruction in the area around the winding or damage to, or misalignment of, the top and bottom pivot points. I used to fix these all of the time when I was a kid - I could see better and my hands were steady(er). The other possibility, if there is no continuity is a broken wire inside of the meter.
Often people give that adjustment screw a couple of turns which will often bend it and the pin that rides in it. Remove the adjustment assembly and realign on the pin.
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Do you mean "stuck" as in "not moving at all" or rather "the zero point is 12?" If the needle is free to move, you can fix it. If it doesn't move at all. you're probably out of luck, if it's a Hickok branded meter.
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Below are 2 pics of the meter. The meter is crimped together really tight, so access is not trivial. Can see the mechanical zero lever moving inside when turning the "zero adjust" screw but nothing happens. The meter does deflect normally to the right with an external power source.
Richard
[Image: http://i170.photobucket.com/albums/u250/...vuofw5.jpg]
[Image: http://i170.photobucket.com/albums/u250/...mdsdcp.jpg]
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It might be then that either the adjustment pin from the spring is not inside the slot of the lever, or maybe the pin broke off.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
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It does sound as if someone turned the screw too far, and the pin came out of the fork or broke off in the attempt to reseat it.
Sometimes discretion is the better part of valor: subtract 12 from all your readings and call it a day.
I see a similar Dixson meter on ebay for ten bucks. Maybe some parts are interchangeable?
(This post was last modified: 07-01-2015, 11:27 AM by
Alan Douglas.)
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Sometimes I saw the pin just broke off flush with the base....not in these devices but in Weston movements in general.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
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Please forgive me for stating the obvious, but have you taken the meter out and tested it? Anyway a replacement should not be hard to find. A gentle knock or two has freed many a stuck movements, your call to proceed.
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Thanks for your interest.
Meter was removed and given some gentle taps to no avail. Could see the pivot inside moving while working the zero adjust screw. Really odd to me that nothing would work. Meter is really crimped together tight so getting inside is not trivial. Meter did deflect normally with an external power source and would do a "line test" in the TV7. At this point the customer sold it on ebay "as is".
Richard
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Keep an eye on eBay, as I often see TV7 meters for sale there.
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