Re: [volt-nuts] Replace neons with LEDs in Fluke 845AB

[Dallas Smith]

Hi Lou,

Its been awhile since I made this mod, but I had the foresight to save 
the project to K04BB's site.


K04BB /Fluke/Fluke 845A AB 



Still works great, hope you have the same results.

Dallas



On 6/5/2016 9:51 PM, Lou Amadio wrote:

Question for Dallas Smith:

I want to replace neons with LEDs in my Fluke 845AB.

Following your instructions below, did you mount the LEDs where the neons
were on the PCB and use the plastic light tubes or did you mount the LEDs
hard up against the LDRs in the yellow foam block?

Thanks, Lou



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Dallas Smith, 2 years ago

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“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.”

Lamp Blocks
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[volt-nuts] Replace neons with LEDs in Fluke 845AB

[Lou Amadio]

Question for Dallas Smith:

I want to replace neons with LEDs in my Fluke 845AB.

Following your instructions below, did you mount the LEDs where the neons
were on the PCB and use the plastic light tubes or did you mount the LEDs
hard up against the LDRs in the yellow foam block?

Thanks, Lou



Quote

Dallas Smith, 2 years ago

Permalink 

Raw Message

Report

“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.”

Lamp Blocks
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[volt-nuts] LTZ1000 project build

[Frank Stellmach]

This whole discussion does not really apply to the LTZ1000 circuit, that 
is the bare 7.15..V output, w/o step up amplifier, as all drift 
parameters were attenuated by orders of magnitude, depending on the 
resistors, R1-R5.


In the eevblog thread, several volt-nuts measured the real dependency, 
in contrast to the datsheet, which simply claims 1:100 attenuation for 
each of these resistors:



R1  R2  R3  R4  R5  author
120 7   7   12-15k  1k  
-1/770  -1/250  -1/1400 +1/100  
janaf
-1/600  -1/238  -1/1000 +1/87   
lars
-1/656  



TiN
1/714   1/250   1/  1/105   
bbs38hot
-1/670  -1/238  -1/1184 +1/74   -1/75   Andreas


Therefore, even humidity effects at most affect R4/R5, with 1/75 impact.

I also think, that it's possible for volt-nuts to measure such residual 
effects, by assembling several references, keeping the parameter of 
question (e.g. humidity or temperature) constant for the master 
reference, varying this paramater for a DUT, and evaluating the drift by 
monitoring the difference between the references.


Same goes for longterm drift, by using a group of many references (A man 
with one, two, three clocks..)


In the end, maintaining ultra precise references at first requires to 
care for controlled/constant ambient parameters, than to put too much 
effort to design references, which are immune to all possible drift factors.


Frank

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