How To Remove the Knob on a Fluke 170-series DMM

Fluke 177 Rotary SwitchFluke 170-series rotary switch knobs can be removed for cleaning and/or lubrication.  The area under the knob can collect dirt and gunk, which will lead to rough operation and possibly even damage to the end stops.  But it may not be immediately obvious how to go about getting it apart without damaging something.  Follow these steps for easy disassembly.

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Fluke 77-IV Copper Corrosion

White residue on 77-IV PCBThe fourth generation of the classic Fluke 77 shares the same basic design and circuit board as the rest of the 170-series (175, 177, 179).  Apparently a common problem with these circuit boards is the appearance of a white powdery residue that collects in certain areas.  A couple have passed my workbench, and I’ve heard reports of more.

The source of this residue is unknown to me.  Chances are, it is probably environmental, perhaps humidity.  What is clear however, is that the residue can be accompanied by the corrosion of parts of the copper PCB traces.  [Added later: best theory is water-soluble flux residue has reacted with humidity to create a corrosive salt.]

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Inside a Multimeter Fuse

Ever wonder what’s inside those expensive multimeter fuses?  This is a Bussmann DMM-B-11A fuse used in many popular late-model DMMs for the 10A current range.  The arc-quenching sand filler and glass fiber-reinforced melamine tube gives it a high rupture capacity (HRC).  It is rated at 1000V (AC or DC) and is capable of interrupting 20,000 amps.

I find it interesting that the zig-zag shaped element has separated into several pieces, no doubt by design.  Fortunately it did its job and the multimeter and forgetful multimeter user it protected suffered no damage.

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Fluke 8020A LCD Replacement

Fluke 8020A LCD ReplacementFluke introduced the 8020A in the late 1970s as its first handheld DMM.  These 3½-digit, 2000-count models can still be found on the used market, and can still be very useable, if they’re in working condition.  Unfortunately though, LCD problems are common on this 30+ year-old device.

This example was obtained rather inexpensively in a group of three derelict handheld meters. (See also: Elenco LCR Meter, Keithley 135 DMM)  The LCD is obviously suffering from some malady that causes it to look dark.  None of the segments can be seen at all. Continue reading

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Beckman Industrial HD110 Multimeter

Beckman Industrial HD110 MultimeterThis 3½-digit 2000 count manual-ranging heavy-duty multimeter is an interesting example of mid-80s technology.  With an impressive safety-yellow thick sturdy o-ring and gasket-sealed case, it looks like it could survive a drop test with the only damages being to the floor it lands on.  Ironically, the most serious damage to be repaired was not electronic, but a broken internal screw post, perhaps due to age and over-tightening.

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Fluke 83 DMM Repair

Fluke 83 Digital Multimeter

The Fluke 83 Multimeter is part of the 80-series that was introduced in the very late 80s.  This unit is the lowest model in the line-up and has a basic DC accuracy of 0.3%.  It does not have an RMS AC converter or a backlight like its venerable cousin, the model 87.

This example arrives without its usual yellow holster and is completely dead.  No display at all.  Inspection of the internals reveals no particular problems, except for the fact that someone has inserted the wrong fuse at the F1 location.  This should be a BBS-1 fast-blow fuse, but a 1A time-delayed fuse has been installed instead.

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