Ian,
I will to the issues in order:
1) My mistake, the electolytic on my board is 10v not 16v. My 10v cap is a little too tall to allow the Wemos board to seat. I just bent the legs (like you do for the MOSFET) and laid it down on the board - there is plenty of room.
2) Regarding the neons: I had soldered the jumper. The Ah-Ha moment came when testing the display board against the plasma ball. The neon bulbs did not light. I tried several new ones from the package, and they also did not light when held to the plasma ball. I now think these are actually neon sparkgap devices, not neon bulbs. They look identical to neon bulbs. I attached a (crappy) picture for your viewing pleasure.
3) Using a plasma ball as a test tool!! Cracked me up - I love it! It worked great. I have attached a picture of the display board held near the plasma ball, and you can clearly see the second nixie tube (N2) is dark.
4) Your recommended tube removal procedure worked great. Breaking the thicker base glass which holds the pins was nerve-wracking. I draped a small piece of cloth over the display board to catch the glass chips as I chipped out the glass with a small diagonal cutter. After cleaning off the attachment wires, I easily removed the pins 1x1. A slightly more difficult issue was cleaning up the pads to accept the new tube. I used a spring loaded solder sucker to suck the solder out of the pin holes, and then tiny drill bits held in my fingers to open up the holes to accept the new tube.
As recommended, I dry fit the new nixie tube and it worked fine. I am going to solder the new nixie and new neon bulbs in tonight. I will measure the voltages and waveforms for fun as well.
I am going to add all your excellent suggestion to my tool box, right next to my diagnostic plasma ball!
Finally, I included a picture of the numeric filaments from the IN-2 which I had to break just for entertainment value. I can see using a flipped 6 and 9, but it still puzzles me why they bothered to use a flipped 2 for the 5 in this, and other, nixies. Could not have saved that much money.
Thanks again for the awesome help, will let you know how the clock runs after the new parts are soldered in.
- Bill