Monroe Electronics Electrostatic Voltmeter - Isoprobe® - model 244A - Manual (Page 19)

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APPENDIX II
10X GAIN MODIFICATION
(For use with high resolution probes)
Due to the smaller aperture in high resolution probes (1017EH, 1017SH, 1017EJ),
electrostatic gain is lowered. As a result, it may not be possible to achieve optimized
transient response except at extremely close spacing.
System gain may be increased approximately tenfold by replacing R63 (10K, adjacent to
A5 in front corner of main PC board near meter – refer to picture) with a 1K, 14 W, 5%
carbon composition resistor.
To replace resistor:
1. Remove cover and locate R63.
2. Remove bottom panel from instrument (two #6-32 screws in center of
side panel).
3. Carefully remove the two #6-32 screws which hold the front panel to the
side rails (screws located just behind front feet) and move front panel so
that it does not interfere with replacement.
4. Unsolder and replace resistor.
5. Re-assemble instrument.
After this change has been made, adjustment of front panel gain will be difficult at close
probe-to-surface spacing when using standard probes. It is therefore suggested that
units so modified be tagged in some manner to alert the unwary user.
Front
Panel