[volt-nuts] Fluke 883AB differential voltmeter

[Alan Scrimgeour]

I also recently restored a Fluke 845AB  Null Detector. I used cheap Nickel 
Metal Hydride batteries to replace the originals, but I was tempted by the 
improving capacities of Low Self Discharge NiMH batteries:
http://en.wikipedia.org/wiki/Low_self-discharge_NiMH_battery

The repair seemed to work very well, but a fault quickly developed: when 
switched to 'LINE OPR' (mains powered) the meter swings to the extremes and 
then settles to zero and won't move again as though it's switched off. I'm 
too busy to deal with that right now, but I was wondering, how much noise 
should I expect to see in the meter needle with the input shorted?

Alan


----- Original Message ----- 
From: "Mark Sims" <holrum at hotmail.com>
To: <volt-nuts at febo.com>
Sent: Friday, March 19, 2010 1:04 AM
Subject: [volt-nuts] Fluke 883AB differential voltmeter


>
> I just finished restoring a Fluke 883AB differential voltmeter (and a 
> 845AB null voltmeter).
>
> The 883 AB needed new battery packs (I used 4 x nine AA cell nicad packs 
> and a 4 subC cell pack)...  remarkably cheap from a Ebay vendor.  The 
> original 9.6V packs used an unobtainium coin cell and would have cost 
> around $200 to replace).  Also the power supply for the AC input converter 
> was fried (transistor, zener, cap).
>
> Final problem was it would not zero properly.  The zero circuit uses two 
> diodes to make a +/- 0.6V supply driving the offset pot.  The unit was 
> offset so that you could not reach zero and the offset pot had fairly 
> little range.  Adjusting the chopper didn't help.  I replaced the diodes 
> with three 1.2V reference chips (making a -1.2 to +2.4V supply).  This 
> centered the zero adjustment and gave better range.
>
> Adjusting the KVD is a pain...  you have to unsolder/solder various 
> jumpers, etc.  Anyway,  it now seems to be working better than new.
>
> Now to the Fluke 515A calibrators.  They have two 18 (AAA?) cell packs. 
> Replacements can be had for $175...  I think I can do better (or will do 
> without).
>
> I also have a Space Labs digital igniter tester (basically a Kelvin ohm 
> meter).  Uses a 6 cell NiMH coin cell pack built into a piece of PVC pipe. 
> One place wanted $600 for the replacement!   Since the unit only draws 11 
> ma while you hold the test button,  I replaced it with a 9V smoke alarm 
> battery / diode to block charging.  Should last forever (and not self 
> discharge in a month)
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