Xref: utzoo rec.ham-radio:12376 sci.electronics:7341
Path: utzoo!utgpu!watmath!iuvax!rutgers!bellcore!jupiter.bellcore.com!karn
From: karn@jupiter.bellcore.com
Newsgroups: rec.ham-radio,sci.electronics
Subject: Converting a Fluke 75 DVM into a model 77
Message-ID: <17373@bellcore.bellcore.com>
Date: 9 Aug 89 20:38:25 GMT
Reply-To: karn@jupiter.bellcore.com ()
Organization: Bell Communications Research, Inc
Lines: 42


I recently purchased a Fluke model 75 multimeter. This is a middle-of-
the-line model in their autoranging handheld DVM series. It differs from
the top-of-the line model 77 by being about $30-$40 cheaper and by
lacking the model 77's "touch hold" feature that allows the meter to
latch a measurement after you remove the test probes. (The model 77 is
also specified to have slightly better accuracy).

A friend in the lab here has a model 77, so on a hunch I decided to compare
the PC layouts. Sure enough, there was one jumper that occupied different
positions in the two models. When I moved the jumper on my model 75, I
discovered to my delight that it had gained the touch-hold feature of
the model 77!

The change is quite easy to make.

1. Turn the unit over and remove the four screws holding the case
together. Remove the case top and set it aside.

2. Remove the 15A fuse at the bottom of the PC board to reveal a single
screw that holds the PC board to the bottom of the case. Remove the
screw and take out the PC board.

3. Holding the PC board with the display at the top, examine the
components just above the function switch. Just to the right of the
calibration pot is a resistor, and just to the right of that is what
looks like another resister but is actually a jumper (it has the color
code of a 0-ohm resistor!) In the model 75, the jumper occupies the
second and third holes of a set of three holes, counting from the left.
Unsolder one end of the jumper from the third hole and move it to the
first hole.

4. Reassemble the unit, taking care to ensure that the function switch knob
shaft position lines up with the switch on the PC board before screwing
the cover back on.

To enable the touch-hold feature, hold down the button in the center of the
function switch as you turn the meter on. To disable touch-hold, turn the
meter off momentarily. (The instruction manual provided with the model 75
also covers the 77).

Phil