Hi Greg, No, not ESD... My friend touched the shell on the cable to an external time source (clock ground) and the label (-270VDC). Not sure exactly what he was doing at the time to touch both, but there you are.
Bob On Friday, January 28, 2022 at 5:28:27 PM UTC-8 gregebert wrote: > 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 neonixie-l+unsubscr...@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/e2d59d81-104a-4051-80d1-d0d90ac0f3b8n%40googlegroups.com.
