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Glad you got it working! Let me know if there is anything else I can help you with.

First, confirm that the voltage from pin 3 to ground is still 2.9V, and the voltage from pin 2 to ground is 0V. This is the issue - if pin 3 is stuck high, then pin 2 should be high as well. Measure the voltage across R5, D2, C3, and R9. Those voltages will help us troubleshoot what is going on. It'...

Can you post a high res photo of the top and bottom of the PCB?

Check the direction of D2 and make sure it matches the silkscreen on the PCB. Also check the solder connections around R6, D2, C3, R9, and U1.

no change

Glad you got it working. Let me know if I can help with anything else!

There is an archived version of that page here: https://web.archive.org/web/20120626122 ... probe.html

There's some information here:
viewtopic.php?f=15&t=487

I suspect most switching NPNs would work fine for Q2. The 2n3904 is just a generic NPN.

The HV transistor needs to be a fast switching type because it is responsible for quickly switching current through L1 in order to generate a series of high voltage pulses that are filtered to create the HV supply. I'd try the STL128DN or a similar transistor - I can't guarantee that it will work bu...

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