If this uses an isolated supply (such as from a wall-wart), you need to touch 2 circuit nodes at different voltages in order to get shocked. Any chance this was from electrostatic discharge (ESD) ?
On Friday, January 28, 2022 at 1:26:31 AM UTC-8 Robert L wrote: > *I just remembered one more hazard... again an issue with the conductive > black layer coming in contact with various voltages.* > > There is a small tab at an interior edge of the label plate sticking out > toward the tube carrier pcb in the middle where the tube carrier connector > is soldered to the tube carrier pcb. This is on the front side of the tube > carrier pcb and is shown in circled the image below. The label plate tab is > a few mm wide and is near the center of the label plate. > > Make sure this tab is clear of and above the tube carrier connector > mounting pins. It is possible to catch the black conductive side of the > label sheet tab on the connector pins when mounting the tube carrier. > > This issue will not be a problem if the label plate is properly installed > with the tab clear of and above the connector pins. > > Again, the same potential problem... there is the possibility of various > voltages coming in contact with the conductive layer... possibly another > shock hazard as there are moderately high voltages on pins in the center > section of the connector. I could also imagine a possibility of damage to > clock circuits depending on which pins touch the conductive black surface. > While the -270V pin is at the side of the connector well clear of the > plastic tab, there are other voltages on center pins where contact with the > label sheet is possible. > > Once again, *make sure the tab is completely clear of and **above all of > the connector mounting pins*. It is possible to catch the black > conductive side of the label sheet tab on the connector pins when mounting > the tube carrier. > > The tab is circled in red in this image copied from the assembly manual. > [image: tab.jpg] > > I think assuring that the label sheet tab clears the tube carrier pins > will mitigate this additional hazard. I leave it to each of you to > determine that the mitigation you adopt is safe and sufficient. My intent > is to make others aware of the hazard so that they can mitigate as they see > fit. > > And once again, best regard, stay safe and well! > Bob > On Friday, January 28, 2022 at 12:33:26 AM UTC-8 Robert L wrote: > >> 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/2f72f2ad-d6a3-47d4-a2c3-5af76bd68720n%40googlegroups.com.
