Electronics > Repair
Yet another Fluke 8050A LED display conversion
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gcwills:
I recently inherited a Fluke 8050A bench multimeter from a friend. However the LCD display had gone the same way as many of the displays in these meters and was very faded and the characters were bleeding.

Fortunately there are several online resources that describe replacing the LCD display with seven segment LED displays:

https://lous.home.xs4all.nl/fluke/Fluke8050Asite.html
http://mrmodemhead.com/blog/gallery/fluke-8050a-led-conversion/

However one such conversion particularly appealed to me. It used the more readily available common cathode displays and I had several of the 14mm displays in stock.
In addition, it eliminated the 50 or so series limiting resistors making wiring up all of the displays easier.

You can see Rich Williams 8050A mod at the bottom of this page: https://www.diyaudio.com/community/threads/fluke-8060a.367928/

Here is an image of my 8050A with the replaced display:



To come are some more images and details of my particular version of Rich's approach.....


gcwills:
The steps I took to replace the LCD:

1. Disassembled the unit and removed the display board
2. Cut the pcb track to isolate the LCD backplane drive at J1 pin 19.
3. Connect backplane pins 2&6 of the 4054/6 to -5V (pins 7/8)
4. Mount the LED displays on a matrix board and glue the board to the display pcb.
5. Connect all LED common cathode pins to -5V
6. Connect all of the remaining pins to IC11-16 (details in the links above)
7. Glue a piece of translucent red perspex into the front panel of the 8050A
8. Reassembled the DMM!

I simplified the wiring as my 14mm LED displays were too large to fit 5 across in the space available. So I used my power sander to grind down one LED display. You can see the "abbreviated" display on the left in the image below. As a result there was no room for a minus sign so my meter dispensed with the minus, rel, HV, db indicators.

lowimpedance:
Looks like there maybe some space above the digits to squeeze a row of LED'S to indicate dB, rel, HV and even minus. You could just put a small label external above the LED'S.
gcwills:

--- Quote from: lowimpedance on September 24, 2024, 09:51:32 am ---Looks like there maybe some space above the digits to squeeze a row of LED'S to indicate dB, rel, HV and even minus. You could just put a small label external above the LED'S.

--- End quote ---

Thanks for the suggestion. Yes those LEDs could be added if required.
gcwills:
A request!

I have spent some time attempting to add a minus sign to my modded 8050A with little success.
Here is the schematic from Rich Williams diyaudio thread:



Earlier 8050A mods that used common anode LED displays used an NPN transistor to decode the "+" and "-" outputs from IC11. In this schematic you can see that Rich used a PNP transistor to drive the common cathode display. However any of my attempts to get the PNP "minus" circuit working were unsuccessful.

Its a long shot but I thought if I put it out there someone may be able to assist?

***EDIT*** See my later post that corrects the wiring for the PNP transistor.
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