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@febo.com wrote: > > Message: 2 > Date: Fri, 16 Nov 2012 12:52:09 +0100 > From: Fabio Eboli <FabioEb@quipo.it> > To: Discussion of precise voltage measurement <volt-nuts@febo.com> > Subject: Re: [volt-nuts] Fluke 343A > Message-ID: <20121116125209.20471b0fsk4s7pih@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@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 >> _______________________________________________ >> volt-nuts mailing list -- volt-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts >> and follow the instructions there. >> > > > ---------------------------------------------------------------- > This message was sent using IMP, the Internet Messaging Program. > > > > > > ------------------------------ > > _______________________________________________ > volt-nuts mailing list > volt-nuts@febo.com > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > > End of volt-nuts Digest, Vol 39, Issue 8 > ****************************************