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

[Lou Amadio]

For Dallas Smith
Thanks for the info. It is in keeping with the original design.
My 845AB 15v supplies are currently down and I suspect the germanium
transistors around T202 may be leaky?.
Am thinking of replacing them with Si transistors. Your thoughts?
Regards, Lou

On Mon, Jun 6, 2016 at 12:35 PM, Dallas Smith <dosmith at outlook.com> wrote:

> 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 <
> http://www.ko4bb.com/getsimple/index.php?id=manuals&dir=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
>>
>>
>>
>> Quote
>>
>> Dallas Smith, 2 years ago
>>
>> Permalink <http://narkive.com/bdOZWNXt.1>
>>
>> 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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