Thanks for the continued support. The LED's may have won the first round (a Pyrrhic victory, for sure) but I am not giving up (yet). Taking the mutts for a walk to clear my head, and prolly reorder parts tonight.

Your analyses of the potential causes for the problems seem valid to me. All I know of operating this Mastech is the little pamphlet it shipped with. Doesn't cover much; includes a couple of recipes for LED disaster, apparently. I definitely was disconnecting the LEDs abruptly and this possibly resulted in some of my catastrophies, since the LEDs appeared to be working fine when I disconnected them. I think I was subconsciously (rather, consciously and ignorantly) trying to avoid a turn-off spike from the PS and in the process spiked them even more effectively.

Anything you can think of to help keep the next batch of LEDs alive will be appreciated.