RR - Fluke 8840a Display
I have been keeping an eye out for a good, name brand bench DMM for personal use for a few months now. Did a bit of research and started looking for a Fluke 8842, 8840, or a 45. Watched some popular auction sites and even CL. These Flukes, especially working ones go for $150+ and well, didn't want to pay an arm and a leg for one. So, during my research, I know that these have VFD (vacuum fluorescent display) that dims after a time. Figured I could get a dimmed display DMM cheap.
I finally came across a 8840a with the AC option 9 and the GPIB options included and had one person bid at $32 with 13hrs remaining! In the description, it stated that they did try some solutions found on the web to get the display working, but couldn't. Long dramatic story short, I placed a bid in the last 2 seconds and won an 8840a!
Previously, I stated that I did research on what type of DMM is best and the best value. I knew the 8840a was going to be the cheapest and it is widely common with hobbyists. But in my search, I noticed there wasn't many documented cases where someone had replaced the VFD with an aftermarket display. I did find one forum post where a user had implemented some LED 7 segment displays and a few LED bar modules. But he had a Fluke 45 and not a 8840/8842 where I could have just used his research. But not all is lost. The 45 has a VFD and basically is the same except for the display driver IC, D7527ACU. The 8840a uses the TMP82C79P IC and a couple of NE594D, which is a VFD driver IC.
At this time, I know that my VFD is dead and I have checked all voltages and they are spot on, so I am now planning on hacking in some 7 segment displays in the place of the VFD. I do have a 4 digit 1.58" Common Anode display and 3x 14mm x 40mm Common Anode displays to start playing with. In other hackers documentation, they are using common cathode displays. So I may order some CC displays just to make my life easier.