Looks like a design problem to me. The proper way to blank a nixie tube is to remove the anode voltage, either by killing the HV power supply or disabling the anode drivers. If you leave the power on and the anodes multiplexing with no cathode grounded, the anode has some capacitance to ground, and the multiplex signal is effectively AC, so some small anode current flows and the gas glows. I had a cathode go open circuit on one of my clocks - it was the '8' of minutes - and when that digit was selected, the whole inside of the tube lit up with a dim diffuse glow. Being as it stayed like that for a whole minute it was quite noticeable. Since in this case it's entire digits lighting up, probably the cathode driver is breaking down. Does it use one of the Russian 74141 equivalents? They're only rated for about 70V and if there is no cathode grounded to pull the anode voltage down, considerably more than 70V can appear at the driver.
The clock probably won't die from this problem for years, but why take a chance? If I were you, I wouldn't use the timer function to turn off the tubes, since the tubes run continuously will last longer than a TTL chip being broken down by HV pulses on a regular basis. -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/1647bea7-9eb1-46c3-87a3-48d077799c8c%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
