[volt-nuts] Finally got around to modifying my Fluke 845ab with LED's

[Chuck Harris]

One thing that might be hosing things up a bit is white led's don't
switch quickly.  They are really UV LED's with a bit of fluorescent
material between the LED and the world.  The fluorescent material will
also luminesce for hours after the LED is turned off.  Perhaps because
the led never shuts off completely, it is biasing the meter up a few
tens of microvolts?

-Chuck Harris

Dallas Smith wrote:
> 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.
>
> _______________________________________________
> volt-nuts mailing list -- volt-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
> and follow the instructions there.