Modular Nixie Clock Rev3 keeps restarting

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9 months 1 week ago #10474 by jjansen
Orientation is good. But one remark. The diode D3 (1N5819) was not included in the kit, instead there was a 1N4007. I had some spare 1N5819, so took one of my own. (and informed Ian about this).


I will do the VIN measurements this evening. Thanks!

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9 months 1 week ago #10475 by Ian
Does it also do it with one or more of the tubes taken off the board?

I couldn't tell - does it always do it on the same digit? I mean always when, say "33:33:33" is showing?

Just another little note: I know you were trying to be extra careful when you did it, but I would snip the header pin on the "HV" side of P1 now that you have chosen LEDs. A header is going to get moved sooner or later and there's nothing good that will come from putting 170V into the LEDs.

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9 months 1 week ago #10476 by jjansen

Ian wrote: Does it also do it with one or more of the tubes taken off the board?

Yes, I experienced resets with a few tubes. Also the osc shows some spikes to zero without any tube, but with only the HV generator on. It stabilizes when the HV generator switches off. This evening I will try with just one tube, just to be sure.

Ian wrote: I couldn't tell - does it always do it on the same digit? I mean always when, say "33:33:33" is showing?

No, it is seems to be random.

Ian wrote: Just another little note: I know you were trying to be extra careful when you did it, but I would snip the header pin on the "HV" side of P1 now that you have chosen LEDs. A header is going to get moved sooner or later and there's nothing good that will come from putting 170V into the LEDs.

I know, will make this 'permanent' as soon as I do some experimenting with neons. Thanks for the warning!

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9 months 1 week ago #10477 by jjansen
I measured VIN on the board with my crappy oscilloscope. But the downward spikes are also visible on VIN during a reset.

The board draws about 200-380 mA (at 12V).

This evening the resets where triggered when touching the crystal. I replaced the crystal with another one. Did not solve the resets / spikes.

I have a IRF540N at home. Would it be useful to test with this mosfet?

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9 months 1 week ago #10479 by Ty_Eeberfest

jjansen wrote: I measured VIN on the board with my crappy oscilloscope. But the downward spikes are also visible on VIN during a reset.

The board draws about 200-380 mA (at 12V).


I'm guessing that a scope trace of current would show an upward spike in current that corresponds to the downward spike in voltage.

If you look at the schematic you'll see the HV generator is a non-isolating boost converter topology. That means that when the MOSFET turns on the inductor is connected directly across VIN and GND, That's perfectly fine as long as the MOSFET shuts back off before the inductor is completely charged up but if the MOSFET doesn't shut off the inductor becomes a short across the power supply.

The gate drive to the MOSFET is a string of short positive-going pulses. There's nothing I can think of that would cause the pulses to intermittently stay high too long but you might want to stick a scope on it anyway. It's more likely that the MOSFET itself is bad, or R18 (which pulls the gate down insuring full cutoff) is defective(?) - you might try reading resistance from MOSFET gate to GND, should see 3K ohms.

jjansen wrote: I
I have a IRF540N at home. Would it be useful to test with this mosfet?


Testing with a replacement MOSFET is exactly what I would do next if it were my board. That IRF540N is only rated at 100V though so it's not a good choice. I doubt it would last more than a second or two before smoking. Do you have any MOSFET on hand with Vds rating of 300V or higher?

Look into it later when the dust is clearing off the crater.

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9 months 1 week ago - 9 months 1 week ago #10482 by jjansen
Thanks for the explanation. Very nice to learn more about how things work!
No, unfortunately I don't have such a mosfet at hand. The current one is a IRF640, Vds is 200V, is this enough?
Last edit: 9 months 1 week ago by jjansen.

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