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 neonixie-l+unsubscr...@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/f941a2c9-e666-4498-ae4a-dc7638898e7dn%40googlegroups.com.
