Does the issue happen more to certain tubes/digits than to others? If so, it could have something to do with the layout of the traces: i'd be especially worried about long runs of high voltage lines parallel to the lines switching the transistors. E.g., in your PCB, the trace at the very bottom (originating out of "M" at the header) is a low voltage line that controls the anode switch transistors, and if you follow it up, it runs parallel to some high voltage lines. The high voltage line's fast switching could induce a smaller voltage spike at the base of that transistor, which could then turn it on. If this is the cause, it probably would show up more to certain digits/tubes than others.
If it's the same for all, then there might be some problem with the program controlling it: e.g. you need to make sure to wait a small while after turning off one anode, then switch the cathodes, then turn on the next anode. Are you doing that? On Tuesday, February 24, 2015 at 1:15:37 PM UTC+1, joenixie wrote: > > Hi Yall, > > I've attached a picture of the display pcb layout and a pdf of the > schematic for it. The cathode drivers are just the MPSA42 with a 100K ohm > base transistor and the collector is tied directly to the cathode and the > emitter is tied to ground. > > -joe > > On Mon, Feb 23, 2015 at 10:58 AM, gregebert <[email protected] > <javascript:>> wrote: > >> >>> I will try the biasing. would biasing both sides help? This would be >>> sort of like terminating the lines. >>> >> >> No need to worry about termination at this frequency, as in reflected >> waves, unless your PCB traces are several feet long... >> I did check the datasheets for the MPSA42/MPSA92 and they are a good >> choice because they have low leakage and high Vceo. >> Therefore *driver* leakage is not your problem; can you post a schematic >> of the driver & predriver circuits ? It could be the predriver. >> >> It's possible the device driving your PNP anode driver is leaky, causing >> the PNP to turn-on slightly. Are you using a NPN predriver --> PNP driver >> arrangement ? >> If so, your NPN device could be leaking 0.1uA and your PNP will conduct >> "beta" times this. This is easy to fix with a resistor across the PNP's >> base/emitter to shunt-away >> the predriver leakage. >> >> It's also possible there is noise entering the predriver; this is where a >> scope will help. If you dont have a scope, then proceed with debugging he >> predriver. >> >> -- >> 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] <javascript:>. >> To post to this group, send email to [email protected] >> <javascript:>. >> To view this discussion on the web, visit >> https://groups.google.com/d/msgid/neonixie-l/6c5852ba-b890-4d1d-b20f-0a4c2ab78324%40googlegroups.com >> >> <https://groups.google.com/d/msgid/neonixie-l/6c5852ba-b890-4d1d-b20f-0a4c2ab78324%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> >> For more options, visit https://groups.google.com/d/optout. >> > > -- 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/31f85a50-6d1e-4c4e-84c9-a064f2235db2%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
