Another quick update. Replacing the 10's hours tube worked fine. So I do indeed have two bad tubes. I've extracted the other bad tube (1's minutes) and will replace it this evening.
Once I got that going -- after tearing out what is left of my hair trying to get all 13 tube wires into the PCB -- I noticed that the decimal point on the 10's seconds tube was not lighting. Closer inspection revealed that not only was it not only not lighting -- it was missing all together. Looks like the connecting tab is there, but no cathode. No glow. Owner is not concerned. <https://lh3.googleusercontent.com/-knlOkmTOlNQ/WC4DNOCnFDI/AAAAAAAAAEk/t0Nf0QLDVOAgyyJgft9B8aCPj6WIvE-kgCLcB/s1600/missing%2Bcomma.jpg> Terry On Wednesday, November 16, 2016 at 2:58:29 PM UTC-6, Terry S wrote: > > 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/fd94d3e7-130e-49e7-8915-f9ce0744b3a9%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
