Excellent suggestions. Here is an update. I do have the schematic -- however I do not have permission from the designer to publish it. I have ohm'd out the entire circuit, anode and cathode sides.
I did check the timing -- as you said, it was in the millisecond range, and no tubes are being skipped. I finally did test the tubes with my sign tester. The working tubes lit up with a nice orange glow. The two non-working tubes lit just slightly, with a purplish glow. This told me there was something different about those tubes. I extracted one of the non-working tubes from the board, and unlike a known good tube, I could not get the individual cathodes to light with the tester. So I am now convinced the clock has two bad or gassy tubes. As of yet, I've been unable to install a new tube -- having trouble cleaning the solder out of the PCB holes. Not my clock, so I'm working very hard to not damage the PCB. Thanks for the help -- I will post updates as I make progress. Terry On Wednesday, November 16, 2016 at 12:00:11 AM UTC-6, gregebert wrote: > > OK, all of the obvious culprits have been ruled out so now we have to > consider weird things. > > Wish you had a schematic, but it's not mandatory. > > 1. With your scope, do you see similar on/off times at the base of each > NPN 'predriver' ? It should be in the milisecond range. Trying to rule-out > the possibility of the control logic 'skipping-over' the tubes that aren't > lit. > > 2. This might be risky, but you could try momentarily connecting the anode > of the bad tubes to the anode of a good tube. You may want to play it safe > and use a resistor of a few K-ohms instead of a short. If all 4 tubes are > off, there's a low-impedance path somewhere. > > 3. Connect a 10K resistor to +170V supply. This will not damage the PNP, > and assuming it takes 150V to illuminate the tube, the 10K resistor will > limit the current to a safe value of 2mA (1 mA per tube). It wont be a > strong glow, but you will see it if the tubes are alive. > > Connect a voltmeter to the other side of the resistor, and GND. > > Next, momentarily touch the resistor (voltmeter side, not +170V side!) to > the dead tube's anode. You should see the 2 dead tubes glow, and see around > +150V. If you see significantly less voltage, or zero, there is a short or > low-impedance path somewhere. It could be the voltage divider, or a bad > tube. You may need to unsolder one or both anodes to confirm > > If the voltmeter still reads ~170 when you touch the tube, and there's no > glow, there could be an open somewhere. You'll need to buzz-out the > connections between the tube's anode pin, anode resistor, and PNP. If that > still fails, then I see no other culprit besides the tubes. > > -- 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/161c1cfd-da4b-48a7-a688-a26faad44a48%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
