Fluke 8050A LED Conversion

A common problem with Fluke 8010A, 8012A, and 8050A bench/portable DMMs is the LCD will ‘bleed’ or turn completely dark.  Replacements are hard to come by.  But if some common 7-segment LCD displays are hacked in, you get a meter that can be read in the dark.

I did this project before starting this blog and did not fully photo-document the process.  But you get the idea.

This is not an original idea.  More 8050A LED conversions from around the web:


25 Responses to Fluke 8050A LED Conversion

  1. Sean says:

    Have you ever done a conversion for an 8010a? Do you have any suggestions or ideas?

  2. William Tang says:

    My Fluke 8050A meter head (LCD) is not showing any digits and I believe the meter is perfectly functional. If I can convert the display to LED, it will be great. Is any circuitry involved and if so can you send me that circuitry so that I can do some conversion of my meter to LED display.

    Thanks and regards


  3. Rob says:


    Just wondering: Did you make or buy the power supply in the photos? If the later, which make/model is it? Great work with the display. I have an 8050A and the display is in very good shape. I use it all the time and, though it’s a manual ranging DMM, I still enjoy it. Great performance for such an old design. Thanks for publishing this.

  4. Alex says:

    I just purchased an 8050a with a dying LCD. Thinking about using your guide to swap for an LED. Is the schematic in the first picture all that needs to be done? Besides the pull up resistor and trace cut on the reverse of the board.

  5. Jaco says:


    Thanks for this mod, it really works very well.

    I would like to know if I can use this post and or content to publish it in our HAM Radio Club News Letter called “QRX” we normally have about 4 publications and we share what we have done in the past quarter.

    Thank you..

  6. Ron says:


    Great work Mr Modemhead! In the diagram, what resistor wattage are you using and is it necessary to insulate all the resistors? How is the LED display board fastened to the front panel? Is it hot glue? Thanks.


    • modemhead says:

      Thanks, it was kind of a bodge job, but even after 3+ years, it’s still working great. The resistors are 1/8 watt. I insulated the connections just to keep them from accidentally shorting to adjacent wire. Probably overkill.

      The LED board is indeed fastened with a small bead of hot glue. You can barely see it in image #10. And if I recall correctly, that excess board sticking out on the left had to be trimmed off because it bumped into something.

  7. Ron says:


    I purchased the prototype boards, resistors and LED’s. The only thing left for me to buy is some hookup wire. What gauge and wattage do you recommend? Thanks.


  8. AC says:

    With the design shown on another web page http://lous.home.xs4all.nl/fluke/Fluke8050Asite.html, the circuit for “+” and “-” used a BS170 MOSFET. You chose to use 3 transistors (2N3906, 2N3904). Is there an advantage to either design or are they pretty much the same?

    It’s difficult to see in the picture, in your final installation, is there plastic film or similar material used as a clear protective cover?

    • modemhead says:

      I just used the BJT’s because I had a drawer full of them. I added drivers for the b&c (1) segments so that one CD4054 pin wouldn’t have to provide current for two segments. Those CD405x drivers are pretty weak, they’re meant for LCDs.

      The “cover” is a piece of translucent plastic salvaged from the front of an old VCR. Remember those?

  9. AC says:

    I ended up using clear plastic combined with tinted plastic film for the cover. It looks pretty good.

    Completed the electrical mod per the diagram. Used Kingbright SA36-11EWA LED’s. Also replaced the original NiCads with two pairs of sub-C NiMH’s. After the mod, the meter displayed a couple of zeros and a decimal point dimly for about a second. Then the entire display became unstable and would display random sets of segments; new announciator LED’s also participate in the random display. Turning the meter back on doesn’t duplicate that initial “good” display. “Scrambled” display is nominally bright. In the process, F3 blew. Triple checked to ensure there are no shorts and all connections are correct. Before the mod, meter was working ok with leaky LCDs. Not sure if the fault is in the display mod or on the main board.

    • modemhead says:

      Sounds like you may have power supply problems. Double check that your battery cells are healthy (1.2V or more) and the connections aren’t accidentally reversed.

  10. AC says:

    Agree. Symptoms suggest something is not getting the correct power supply. The meter worked for a couple of minutes last night but some segments did not light up. Then the display became unstable again.

    I measured the expected -5V on pins 7 & 8 on U10 – U16, so I think the source of the problem is on the main board. Each pair of the new batteries are putting out 2.8V. I also selected the 3 zener diodes as convenient places to check and voltages were on spec. I’m still looking for more places to check. Perhaps the fault is due to one of the electrolytic capacitors…

  11. Barry says:

    You certainly do nice soldering work. Nice job! I plan to do this to my 8050A as well. Thanks for the great rundown and pictures.

  12. Barry says:

    Can you comment on the need for the 100k resistor from U12 Pin 6 to ground?

    • modemhead says:

      J1P19 is the LCD backplane clock (BP) which is a square wave at about 50Hz. This signal is distributed to all the CD405x driver ICs. It is also the common line for all LCD segments. The driver ICs would normally drive all LCD segments that are supposed to be “on” with an inverted (180° out of phase) copy of the BP signal. Segments that are supposed to be “off” just get a non-inverted copy of the BP signal. This keeps the average voltage across each LCD segment at zero, whether on or off, because LCDs are damaged by a constant bias in one direction (DC).

      To convert to common-anode LED operation, we need each active segment to be driven low and stay there as long as the segment is supposed to be on. So cutting the BP signal from J1P19 and pulling up the CD405x inputs to a logic high will accomplish this.

      U12P6 is just a convenient place for this 100K pull-up. And since the CMOS drivers are powered by the meter’s -5V rail and ground, logic high (Vdd) is actually ground.

      • Barry says:

        Okay, thanks for the reply. I have seen some of the other similar solutions online but I don’t recall seeing this in those designs.

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