Finally got around to modify my Fluke 845ab with LED 's for the chopper
circuit. Used the 17 volt windings for LED's (Mouser
941-C513AMSNCW0Y0511 Warm White Round LED) instead of the 130 volt, move
red wire on transformer pin 9 to pin 7.This winding is 180 degrees out
of phase, so I reversed the steering diodes (CR106 & CR107) I left in to
help make sure the phase was correct for the LED's when connecting.
Change R154 to 6K to set the brightness, selected for good operation of
the zero control. Then install jumper to replace C119. Also changed the
filter integration response caps C111 to .022uF and C116 to 47uF, this
stabilized the jitter to a manageable mode of operation. Meter now works
as well or better when the original neon's worked.
As the meter originally had this problem, why is the offset reading
different when polarity is reversed at the meter input? About 10uV's.
Lamp Blocks.
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