170V does not have high enough voltage

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3 years 4 months ago #7467 by nullpoexc
I have assembled half of the nixie clock kit. Now I finished RGB LEDs and they can light up according to the correct startup procedure. However, the 170V test point does not have high enough voltage.

I got the following voltages at these points:
VCC: 5V
Vin: 9V
170V: 10V in DC, 20V in AC
HV5 (feedback input): ~0.1V

No part got excessively hot, and I believe I have soldered them correctly. I have no idea what's going on. If you can see anything from the picture please let me know. Thanks!
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3 years 4 months ago #7468 by Ian
Did you try a factory reset? (Hold down the button while powering on)

Do you hear any faint "crackling" sound?

This should cause the RGB LEDs to flash random colours for abou 10 seconds, and then go into the High Voltage Generator calibration routine.

It seems that the controller is working, (you are getting more than VIN at the HV test point), but it is not working at full power.

The HV calibration runs when you first turn on the circuit, and if it finds no load, it turns itself right down, and because this has a tiny duty cycle, it can look to a meter like the voltage is low.

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3 years 4 months ago #7469 by nullpoexc
Factory reset does not help (LEDs flashed, but the voltage is still ~10V)
I cannot hear any crackling sound when it's operating. Where is it come from?

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3 years 4 months ago #7471 by Ian
The crackling sound (it is very faint, you have to listen carefully to hear it) comes from the modulation of the HV generator: it runs only when we are displaying digits.

What are you measuring the 10V with? Do you have an oscilloscope? If so, please look at the waveform at the gate of the MOSFET to see if there is any pulse there.

It is good that the LEDs flash, that means that the controller is working.

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3 years 4 months ago #7474 by nullpoexc
I have retested it with some new instruments this time. With a 9.00V power, I can only get 8.31V output at 170V. Vcc seems correct (4.96V, very stable). I still can't hear any sound from the board.
I also took the waveform at MOSFET gate, at 2 different time scales. These are really weird...
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3 years 4 months ago #7475 by Ian
The scope traces are fine: The weird waveform is because we only drive the MOSFET when the tube output is enabled. The reason why is a bit involved:

We calibrate the HV Generator during the factory reset to hit 180V when the tubes are on full duty cycle. However, when we are dimmed, the tubes are only on for a short part of the cycle (around 10%), and if we left the HV Gen running with no load, it would ramp the voltage up while the tube is not lit, and this would cause the digits to be lit unevenly. Therefore we turn off the HVG when the tube is not lit.

The waveforms you see are exactly what they should be. There are short pulses of activity (because the LDR is not installed and the clock thinks it is dark), and inside each of these pulses, we see the HV generator square wave.

So the problem can be localised to either the MOSFET, the diode D2 or the high voltage capacitor.

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