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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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mechanical zero on a small meter
I have an old MFJ SWR meter with a built in counter. It has an LCD
display to read frequency and it uses a small 2 inch korean made plastic analog meter to read SWR. I keep this unit in my service truck wrapped up, however it may have gotten jarred because the unit still works fine but all of a sudden mechanical zero is up about ten percent of full scale. There is no zero adjustment accessable through the front of the instrument. This is a nice little unit however to adjust mechanical zero you have remove the analog meter and open the case. This requires complete disassembly of the entire instrument and it is a real pain. I did this and opened the small meter and adjusted mechanical zero. This is a simple procedure however the problem is static electricity. Depending on how I hold this meter, touch it, rub my finger or even a piece of cardboard near it, mechanical zero may shift. At times I think that I have it zeroed and I close the case up only to find that zero has shifted. Then I touch it wirth my finger and zero will sometimes shift again. So the problem is that I don't know if after I touch this thing if It is totally discharged and it is really at zero or if static electricity has influenced the position of the needle. This simple job is really driving me nuts. It is very dry in the house and I'm sure that this may have something to do with it, but I just don't know how to compensate for this. Obviously it is important that my adjustment is correct as there is no access to it once the unit is re assembled. Can anyone offer any advice? Thanks, Lenny. |
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