Not much repair activity lately, but in honor of Halloween, note that a photo gallery of cheap multimeters of the “Harbor Fright” variety has been posted. New also is a quick look inside the Weston 6100 Roadrunner.
The Fluke 26-III and 79-III models are identical except for the model number. This model adds some extra features not available on the 77-III (and its identical twin the 23-III), like frequency and capacitance measurement, 4000 counts vs. 3200, RMS response, and a faster update speed. It also has a special 40-ohm resistance range that provides 10 milli-ohm resolution, aimed at electricians who may want to measure and compare contact resistances on relays and switches. It’s not a bad tool for the electronics workbench either, provided you do not need precise measurements of current in the micro-amp range. It does however have 1μA resolution in its lowest current range (4mA).
No this is not about green energy or climate change. It’s about DMM repair, of course. I found it interesting for two reasons, the fact that a very simple fault almost escaped detection, and that the root cause was, while totally obvious to the naked eye, possible to dismiss as just a cosmetic problem.
The victim in this case is a fairly recent Ideal-branded multimeter, a model 61-481 (from Taiwanese maker APPA Technology Corp.) It was the subject of a teardown post over at the EEVblog forum, and then passed by my workbench on the way to someone else. The DMM was described as basically working, but acting a bit funny and not reading voltage correctly in some ranges.
Posted in Repair
This is probably the single most common problem with older Fluke DMMs such as the 83, 85, 87, and 88 models. Referred to as “faded digits”, “faded segments” or “fading display”, it happens when the connections between the printed circuit board and the glass display panel become contaminated enough that the liquid crystal display (LCD) does not receive enough charge to flip all it’s little crystals around and become nice and opaque.
Does your Fluke 179 have a loose kickstand (tilt stand, tilting bail) that pops out whenever you try to prop it up for use on the workbench? Blog reader LDSisHere from over at badcaps.net contacted me with this problem, and together we came up with this solution. So the following is a new feature on this website, a reader-contributed repair!
This problem can happen on any of Fluke’s “tapered” style meters, including the 175, 177, 179, 77-IV, and also most of the 7x-III series as well. It happens when the plastic crumbles around the joint that forms the hinge where it is supposed to be firmly snapped in place.
Properly-designed multimeters that are suitable for professional and trade use have a number of components, usually near their input jacks, that are for the sole purpose of protecting both the user and (secondarily) the multimeter itself from over-voltage and over-current situations. Everybody knows about fuses and can probably recognize them right away. But the fuses are only used to protect against having too much current passing through the meter and test leads when using the Amp and/or milliAmp jacks.