Weston Analyzer Model 980


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I'm working on this old Weston Analyzer Model 980 VOM.

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I haven't found a manual for the plain Model 980, but I did find a manual for the Model 980 Mark II. Anyone know of a source for a manual for the original 980?

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The range and function switch uses tracks on the PC board. When I received it, the ball-bearing for the click-stops was rattling around inside the case. It's supposed to sit in the little hole in the brass leaf-spring to the right of the switch shaft.

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Unlike the Model 980 Mark II, the plain 980 doesn't appear to have any meter protection diodes.

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The 980 Mark II schematic says the meter should be 50 µA and 1125 Ω.

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Mine measures 98 Ω, and I put up to 3 mA through it without budging the needle. The movement works freely for the most part. It does stick a little at about 3/4 scale. This must be from corrosion on the bearings, as there isn't any crud in the gap.

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I pulled the meter movement out of the case to inspect it.

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The rear pivot looks OK. I can see the connection to the winding on the bobbin. I can't see any damage to the winding. The insulation on the pivot looks good, too.

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The front pivot also looks good.

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As on the rear pivot, I can see the connection between the front pivot and the winding, and the winding looks fine.

Any ideas on the source of the partial short circuit? I can't spot anything, so I'm left supposing that someone overloaded the meter and cooked the insulation on the winding somewhere where I can't see the damage.

I suppose I could take the movement apart and try to rewind it, but that seems like a bear of a job.

© Steve Byan 2011-2016