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Chuck checks out forums on test equipment

And answers some tough questions

By Chuck Newcombe

May 2013

It’s amazing what you can find in the chatter on the internet.

Recently I went looking for information about the CMOS integrated circuit used in Fluke’s first handheld DMM (digital multimeter), the 8020A, which was introduced in June of 1977. One of the things I found was a discussion among amateur radio enthusiasts about a later Fluke product known as the D800. Here is some of that discussion.

I have a Fluke DMM, model D800, in good working order. The PC board is marked "80XX Series," and matches the schematic for an 8020A, but the switches are not labeled with the conductance function. I do not have a D800 manual anymore, so I have a couple of questions that the fine people at Fluke and Intersil were unable to answer.

The questioner had apparently tried to get answers from Fluke and the maker of the CMOS circuit, Intersil. Given that the product in question (which was still working fine, by the way) was manufactured during or before 1980, the inability of people at Fluke or Intersil to answer his questions is not all that surprising.

Here are two of his questions, circa 2010:

  1. Is the D800 a “crippled” version of the 8020A, or is the conductance function merely an undocumented feature of the D800?
  2. U8 is labeled “429100.” My Google-Fu [Zen of Google] reveals this to be "NSN 5962-01-110-1555," leading me to believe that the D800 may be a Mil-Spec version of the 8020A. Can anyone confirm this?

I may be able to answer these questions…

As a member of the product marketing group at Fluke at the time, I may be able to answer these questions.

To answer the first question: The D800 was an attempt to sell a version of the 8020 through alternate distribution channels with a different feature set. The D800 was differentiated by a different case color and a reduced feature set, keeping the 8020A as the premium model.

I truthfully don’t remember whether conductance was an undocumented feature or not, but one could easily test the premise by placing the D800 in the kohms function and then pressing the 20M and 2000k buttons at the same time to get them to latch down together. If the display goes from the over range 1 _ to 00.x, then the conductance mode, scaled to 200 nS, is active. If the display remains in the over range state, then the meter has been “crippled.”

To answer the second question: The D800 was not a military model. Several special versions, and even the standard commercial product, were purchased by various military organizations, and they, not Fluke, assigned NSN numbers to replacement parts as standard operating procedure.

FS: 8020A Main IC, P/N 429100

On another forum, I found the following note:

FS: 8020A Main IC, P/N 429100 A while ago I got an 8020A handheld DMM with a bad display. At first I thought the main IC was bad, so I bought one. It turned out to be the display itself, not the main IC.

It turns out that the LCD display used in the8020A was one of the first units produced that was larger than the small ones then in use for wrist watches. It took Fluke and its suppliers a while to perfect the larger format with good temperature and humidity tolerance. Fluke regularly replaced displays that failed under warranty, and later even provided replacement displays at no cost to customers who wished to replace their failed part. The company supported the 8020 family that way for about 20 years after production was halted.

A really innovative solution

Note the old failed display beneath the repair detail.

Finally, I found a comment from a really loyal Fluke 8020A owner, who had a really innovative solution to the failed display problem. Check it out.

Just thought some may be interested in my rebuild of the LCD display on an old Fluke 8020a handheld meter. What I did was to buy a 3.5 digit LCD (cheap) with through-hole pins, and then modified the plastic mount for the old display so the new one would fit nicely and the slide in cover would keep it in place.
Next for the fun bit was to use wire wrap wire to connect the new LCD to the pcb pads where the old “Zebra strip” was.

Continuing his description of the restored meter (30 years after original production and calibration):

The calibration is in spec. and has been checked on a calibrator at work. Some may ask why bother, the answer is because I hate to see a good meter end up in landfill and I got a fully functional meter to add to my collection. – John

John’s experience with regard to the calibration and performance of his 8020A so many years later is not unique. I just checked my 8020A, and found its calibration in spec. as well. And, for the most part, I think recent Fluke DMMs are likely to perform in a similar manner. Rugged and Reliable is the name of the game.

One word of caution to experimenters like John - great care was taken in the design of these products to make sure that insulation creepage and clearance distances of electrical components were adequate to meet claimed safety specifications. While such modifications are probably ok for use in low energy bench applications, I don’t recommend using a meter modified in this way on high energy electrical circuits.