Hi Terry, I guess I could have been more clear... The label plate ink is only *moderately* conductive; black ink on a somewhat flexible white substrate... the label is not FR4 pcb material and there are no metal layers. I have no experience using this material and am just letting you know what I saw looking at the sheet on my friends clock. Both photos show pretty good detail of the sides of the label sheet.
I measured about 18K between each pair of two side case screws securing the label plate. I measured higher resistance side to side between the more widely spaced pairs of front and back screws. Again, moderately conductive. Obviously no conductivity to speak of for the laser cut plastic case parts that the retaining screws screw into. I was able to measure the high voltage with one probe gently resting on the black ink surface. Lightly touching the black paint with the rounded side of a probe tip was sufficient. I did not need to touch the metal screws or use the sharp probe tip to break through a surface layer in order to measure voltage. The flexibility of the printed sheet likely contributes to the problem. The sheet was able flex a bit to make contact with the pots. Moving forward, my friends two clocks are packed and will be in the mail tomorrow. I no longer have a clock that I can look at or experiment with. Again, all best regards, stay safe and well! Bob On Thursday, January 27, 2022 at 8:10:27 PM UTC-8 Terry S wrote: > Is this printing on a PCB? Not clear from your photos. > > It seems unlikely that ink used on a PCB would be conductive. > > > On Thursday, January 27, 2022 at 2:52:25 PM UTC-6 Robert L wrote: > >> Hi folks, >> >> A friend received a rather nasty shock from one of his Mr. Nixie ITS-1A >> clocks... To add insult to injury, he dropped the clock when shocked and >> two tubes were broken. >> >> I've repaired his clock and, in the process, identified and mitigated the >> shock hazard. Note that I am not connected with Mr. Nixie. I'm simply >> trying to help others avoid this nasty experience. >> >> Here's what I found... >> >> 1) The black bottom case cover with labels for "SET", "ADJ" and "ALM" is >> likely printed using a carbon black based ink... Whatever the ink used, >> it's conductive. >> >> 2) There are 6 trim pots on the tube carrier assembly used to >> individually adjust -270V supplied to each of the six tubes. Tabs on the >> trim pots are directly over the conductive black printed base plate. >> >> The trim pot mounting tabs on my friends clock had come into contact with >> the conductive printed label. My friend touched the label and a grounded >> piece of the clock and was rewarded with the rather nasty shock. >> >> The photos below show the mitigation I used on my friends clocks. >> >> The mitigation is to assure that the trim pot tabs do not contact the >> black label plate. I added a triple thickness of Kapton tape between the >> trim pots and the label plate on his clocks. This may not be the best >> possible solution, but it's a starting place. I leave it to each of you to >> find a mitigation that you feel is safe. >> >> I urge you to check your ITS-1A clock for this hazard and mitigate as you >> see fit. >> >> I used a DVM to measure the voltage with one probe to the supply ground >> and the second probe touching the black printed label. I could also measure >> resistance between these two points with the clock unplugged. There should >> be an open circuit between these points - no voltage / open circuit >> between these points. >> >> A visual check will let you see if there's clearance between the trim >> pots and the label plate. I strongly recommend that you mitigate the hazard >> - clearance or not. At a minimum, I think that you want a non-conductive >> barrier between the trim pot tabs and the conductive label. >> >> Trim pot tabs are very close to the conductive label plate on the clock >> shown below... tabs were touching on the clock that shocked my friend:: >> >> [image: PXL_20220127_175801532.jpg] >> >> This is the clock that shocked my friend. The photo shows a triple >> thickness of Kapton tape separating all of the trim pot tabs from the label >> plate. Tape is held in place by adhesive backing and is also trapped >> between the tube carrier and label plate: >> >> [image: PXL_20220127_180629685.jpg] >> >> This hazard and a possible mitigation posted here in the hope that it >> prevents others from receiving a nasty surprise! >> >> All best regards, >> Bob >> >> >> -- 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 view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/f68dbaf8-e04e-4ac6-8c6a-3b073f325990n%40googlegroups.com.
