Continuing on from my previous update, the non working display is first on my hit list for this post. I’ve checked the cables and swapped the displays around to verify that the issue is indeed with the display itself. Last time, I tested the two UDN6118 chips on the display and they were OK. I did this on the chip pins however and not the solder joins on the rear of the board. This time, I flipped the display over and tested the chips using the joins. Both tested OK again. After some further research I decided to modify an old power pack that can refresh the displays by burning off the crap that becomes attached to the filaments. I was hopeful that the issue was simply a very faded display. For this, I found an old powerpack for a 28.8K modem I purchased back in 1995 or something. I’m amazed I still have it. It’s rated at 9V and 500ma. I replaced the connector with two alligator clips. I put some red tape around the positive lead.