Initial tube hook up killed High Voltage at test points

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1 year 3 months ago #9777 by Dan1066
Building the Nixie classic with RTC using IN 12 tubes. Completed building circuit board. Had 200V at test point after completing HV portion of board.

Completed the circuit board, hooked up RTC, tick LED, RGB LED, LDR and button. Still had 200v at test point and everything worked as expected.

I hooked up two tubes per the instructions. Lamps did not light. Performed factory reset, LEDs gave indication of reset finishing. Now I have no HV at the test point. Voltage between the HV test point and GND test point is around 2V.

On power on, I do have 170v on the middle leg of Q1 for about 60 seconds.

I would appreciate any next troubleshooting steps.

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1 year 3 months ago #9778 by Ian
That's totally normal: The HV generator only runs for 60 seconds when in test mode. When you tell the clock to exit test mode (press the button when all the digits show "88:88:88" it will go on to the HV calibration and then normal run mode.

The reaosn for this is that when you are in test mode, the clock has not yet done the calibration yet, and depending on what the state of the clock is, this could cause the circuit to overheat.

As long as you are getting HV for 60 seconds, you are tine!

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1 year 3 months ago #9782 by Dan1066
Ian,
Thanks for the quick reply.

I only have HV when I probe the middle leg of Q1 and ground. I do not have HV when I probe between the HV test point and ground test point. Is this normal as well?

Dab

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1 year 3 months ago #9783 by Ian
That's not normal: The test point is there just for the purpose of testing the HV. Please check that the diode D2 is the right way round. The white stripe on the diode should be closest to the square pad.

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1 year 3 months ago #9787 by Ty_Eeberfest
I'll toss out a couple more troubleshooting thoughts...

Try taking the opto-couplers that correspond to the anodes of your installed tubes out of their sockets. Does HV work now? If so, the problem almost certainly is in your tubes / tube wiring.

If that didn't solve it, consider these things:

The HV takes a long and winding path from the HVG area of the board over to the test point. Any chance a trace got cut or shorted, perhaps by some stray stuff on the work surface, while hooking up your tubes?

Do you have HV at the + terminal of C1 (2.2uF 400v)? If so your D2 is okay.

If you have HV at C1, I'd start checking all the places HV should be found, trying to isolate where it gets lost. Try reading the HV OUT pin of SV1 (4-pin power header) and Pin 4 of every opto-coupler.

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

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1 year 3 months ago #9796 by Dan1066
Thanks for the quick replies. Did the following
1. Checked D2 orientation. It was as it is supposed to be.
2. Checked voltage at C1. No high voltage
3. Checked input of D2. High voltage present.
4. Checked output of D2. No high voltage

So I think this means D2 is bad and needs replaced?

Dan

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