{Collins} Calibration Difficulty -Military HP-410B Clone





 Collins Group;

 I'm having difficulty in calibrating the AC scales of  my
 Military Clone of the HP-410B VTVM, designated Multimeter ME-26D/U,
 manufactured by Sentinel Electronics, Inc.

 This is a ruggedized version of the venerable HP-410B, and has a somewhat
 upgraded circuit, but is the identical in many respects.

 It uses the 2-0!C diode in the AC probe, which appears to be functioning,
but with some concern.

 The problem involves the lower voltage scales primarily....... the 1vac,
3vac, 10vac, 30vac particularly, but apparently accross the whole AC scale,
while the DC voltage and Ohm scales function  properly.

 The calibration pots range does not compensate for the lower than actual
 voltage indicated on the meter....... namely with 1vac to the probe, the
 most I can get on the 1vac meter scale is about 80% of the actual applied
 voltage and the same is true on the other scales.

  I have accomplished all of the usual tests.... adjusted the probe diode
 voltage to the proper 5.0 volts, checked the tubes and measured other
voltages, cleaned the pots and rotary switches, etc.

 Any thoughts....... I suspect the diode, but would it fail in this "80%"
manner?

Comments will be appreciated.

73/jim/W0JJL

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