TI-45: Rejuvenation of a faded VFD-Display

[voltaage]

Thank you Pjwum for the post!

I tried to do this on one Elektronika MK 61 of mine which had a very, very dim, unevenly lighted display. In my case, the voltage through the filament had to be between 12V-15V to make a difference. Initially I went for 8V but the filament was not glowing at all, even with a couple of cycles I couldn't get the digits any brighter so I opted to raise the voltage.

This calculator was such a pleasure to work on since each end of the filament is directed through a daugther-board that does all the voltage magic. I had to cut two of these wires that the small board used to hook up to the main pcb to make sure the voltage was applyed solely to the VFD, so no other component could blow up. When monitoring the improvements I just re-soldered the wires each time to power up the calculator. After I was satisfied with the results, those tinned wires had to come out, nothing that some donor resitor legs can't help with.

The number of times I've seen a worn VFD is very reduced. My local supermarket has one IBM-branded POS information pole (I'm not sure how you'd call these things) that dates back from the early 2000's. That's thing has been on literally, 24/7 for the last 22 years and no fading, no unevenly lighted portions are present.

My MK 61 has a very unique display. Most of the models I find online only have the -88888888°88 layout, whilst mine is arranged as 888888888888. Any dedicated digit for the sign display is just a simple middle segment for your regular "8". Probably the earliest ИЛЦ2-12.8П tubes were like this before realizing that is was better to leave just the bare basics. While true, under normal circumstances using the -88888888°88 layout is fine, I found some tricks to trigger the use of those segments that shouldn't.

Therefore, I had no choice but to work on the old part, which gave great results.