OK, reading through the thread, it seems to me that the MOSFET or the inductor is the culprit, and when the high voltage circuit starts to go wrong, it loads the power supply and this causes the 5V line to drop.
Once that happens, we no longer have the gate voltage to drive the MOSFET full on, and we go into meltdown.
I can think of three possible causes here:
1) The MOSFET has a high switch on voltage that the controller can't reach and this means that the FET stays partially in the linear region and heats up. Unfortunately, a hot MOSFET has a higher transition voltage than a cold one, and this has a runaway effect. More heat means worse switch on, means more heat.
2) The inductor is out of spec (<<100uH) and saturates, causing the MOSFET to short the supply, getting hot and running away.
3) The controller is either running below the required frequency, or has an unstable clock circuit. If the frequency drops, even temporarily, we go into 2)
At the end of the day, we have a "get you going" guarantee, and if you've had it with this board, let me know and I'll repair or replace it, giving you a fully assembled board if you want, or a kit, or a set of parts to substitute. Totally what works best for you is the best option for me.
I wouldnt say i had it with this board, but i need to know that i can trust it, i believe that if the overheating of Q1 happened at nighttime it could have started a fire, i hope that i am wrong.
I wouldnt mind a new kit, but in a way that feels like i am ripping you of as this probably could have been fixed with a few new components, my problem is that i am not capable of telling which components needs replacement, and if the issue is truely fixed...
What would you suggest as the best solution for both parts?
If you dont want this discussion public, you have my email.
My $0.02 worth... it depends on your desoldering skills and equipment. I've found these boards to be very easy to damage when trying to replace parts. One false move and you end up with a cut trace.
If you have a high(er) end desoldering tool, e.g. Hakko 808, or exceptional skill with desoldering braid, then replacing the MOSFET and inductor should be okay (unless the real problem turns out to be Ian's Item 3). Otherwise accept the offer of a new kit and make a fresh start.
I doubt the MOSFET could start a fire. Most likely it would fail internally and stop conducting before it got hot enough to ignite itself. If you have it in direct contact with a wood or plastic case it might be a different story though.
Look into it later when the dust is clearing off the crater.
Why don't we do it like this? Send the board back (less tubes - take them out) and I will exchange it for one of mine which has gone through a test cycle. I'd also like to inspect the components in any case, and figure out what happened.