[volt-nuts] Fluke 343A

Dick richiem5683 at gmail.com
Sat Nov 17 00:54:23 UTC 2012

Hi Fabio -- nice work on the LEDs -- easy when the original Fluke posts/lenses are still there from the old lamps. My second 343 only had one of the orig. posts in place, so i removed it and used black plastic LED panel mounts for the replacement LEDs.

I went ahead and opened up my LED-version 343 and it has 2.2k 1W resistors for R180 and R181, which are the limiters for the range lights and the ON light -- this runs them at around 12mA. These 4 are supplied from a 28VDC supply. Overkill wattage on the resistors, I think. The LEDs in the previously modded second unit are sufficiently bright at 5mA -- I think 10mA or more is too bright -- just want a clear indication in normal room lighting (my lighting is fluorescent).

Dick Moore

On Nov 16, 2012, at 4:00 AM, volt-nuts-request at febo.com wrote:

> Message: 2
> Date: Fri, 16 Nov 2012 12:52:09 +0100
> From: Fabio Eboli <FabioEb at quipo.it>
> To: Discussion of precise voltage measurement <volt-nuts at febo.com>
> Subject: Re: [volt-nuts] Fluke 343A
> Message-ID: <20121116125209.20471b0fsk4s7pih at webmail.micso.net>
> Content-Type: text/plain; charset=ISO-8859-1; DelSp="Yes";
> 	format="flowed"
> Hello,
> I cannot help with the original schematic, but
> I replaced the lamps of my unit with leds.
> I didnt know that there are units wiht leds from
> from the manufacturer, I'd like to know more
> about this also.
> What is the problem you found with the conversion
> of your unit? There can be problems with this conversion?
> I replaced the lamps with high efficiency orange
> leds, with 1W 2k7 resistor in series, so to have
> about 10mA of current, the resistors will dissipate
> around 230mW.
> Mechanically they fit nicely with the help of
> a little heat shrink tubing.
> Here are 3 pics:
> http://www.flickr.com/photos/14336723@N08/8190772946/
> http://www.flickr.com/photos/14336723@N08/8189690069/
> http://www.flickr.com/photos/14336723@N08/8189689929/
> Fabio.
> Dick <richiem5683 at gmail.com> ha scritto:
>> Hi nuts, thanks for your help with the Fluke 343A. Replacing the  
>> p-MOSFET and two 5uF/15V caps, C37 and C42, fixed it up just fine. I  
>> checked D and ESR on the other caps in the chopper circuit, and they  
>> were good. I've cal'd it with my HP 3458A,and it's working very well.
>> Now I have a second 343A to bring back from the dead. Some previous  
>> tech had replaced most of the 7387 lamps with LEDs, and didn't do a  
>> very good job. Trouble is, I can't find a schematic for the LED mod  
>> to the 343 -- the one I just fixed has them, but I'd like to know  
>> some recommended resistor values for current limiting the LEDs. Some  
>> are fairly obvious, but I'd like to be able to confirm values. If  
>> anyone has a circuit diagram for the later 343s that have LEDs, I'd  
>> be happy to pay for copying or whatever.
>> Dick Moore
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