Finished product is looking good! I'm glad the clock is finally working right and I appreciate your sticking with the "long distance" troubleshooting and following up.
I'm not sure what to think about the failing IRF-640s but yes, the change from 840 to 640 is certainly suspect. I think I will do a little bit of research this weekend into what MOSFETs might be available now that are sturdier and have ultra-low Vsd (and that don't cost a fortune!).
Look into it later when the dust is clearing off the crater.
Ian wrote: That intrigues me. I see no reason why replacing the MOSFET should have solved the problem. Do you still by any chance have the faulty MOSFET? If so, I'd like to investigate it. Perhaps it has a gate problem... I really don't know...
Where you able to investigate the problem of the MOSFET?