Vacuum Tube Voltmeter IM-18

[Frank McElroy]

Is there anyone out there who has thoughts on repairing an ill IM-18.

Years ago the unit worked great, now there is not enough range on the
pot to do a DC calibration with the probe in the DC mode (there is if
the probe is not set to DC). When the DC+/- is balanced with a high
range setting I get about +0.3V at the 1.5V range setting ( I can
rebalance but I didn't have this problem before). Also, I can't adjust
the zero and ohms for full scale when the range is in the highest range
settings (I can for the lower range settings). I changed the two tubes
and battery without success.

In looking at the schematic, I'm wondering if R24 at 3.3M has really
increased in ohms and whether this or something else is causing the
above problems. Before getting more involved in changing parts, has
anyone seen this problem before and knows a fix?

73,
Frank, KD2BM

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