Joe -- the anode driver I "borrowed" from the open-source clock looks slightly different than yours. It uses the same transistors, but the MPSA92 has 100K directly across the BE junction, and a 470K between the MPSA42 collector and the MPSA92 base. In other words, imagine moving your R22 to the left of R21, and making R21 470K. (Temp 10 tube) Also, mine has a 33K from the driver to the base of the MPSA42, as opposed to your 100K. A little stiffer drive. I'm not saying either one is better -- just pointing out a difference. I haven't built this circuit yet, so it may need tweaking. I do think Niek has an astute observation regarding coupling -- I went to great pains in my layout to keep the low V drive circuit lines short and far away from the high V switching noise. Put my driver pairs right next to the decoder, and the lines from the connector to the decoder are as far from anything else as possible. Observing what flickers on and what other lines are switching at the time should point you right to the crosstalk source. Terry S. On Tuesday, February 24, 2015 at 6:15:37 AM UTC-6, 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 <greg...@hotmail.com > <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 neonixie-l+...@googlegroups.com <javascript:>. >> To post to this group, send email to neoni...@googlegroups.com >> <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 neonixie-l+unsubscr...@googlegroups.com. To post to this group, send an email to neonixie-l@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/b1588d4e-55f7-4d6d-b3ff-c399857d684f%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
