On Tuesday, December 20, 2016 at 11:11:50 AM UTC-5, N_Cook wrote:
Dropped on hard floor and now just 1/2 second LED illumination.
No sophisticated chippery inside, an LM324 and 2x TL494, no SMD unless
under something.
No obviously failed solder joints of big lumps or elsewhere , no cracked
pcb.
4 IRF740 and 4x RFPN06 and a 7812 complete the main active stuff, what
would be most likely mechanical failure inside? DIP IC, transistor,
diode, other?

Look wherever something heavy is attached to something light, and at some angle other than aligned to the drop force. Anywhere there is heat at such a connection, irrespective of the angle-of-force.

This will be something that bright light and a magnifying glass will reveal along with the usual 'wiggle-it-a-little". And, as you are not getting _any_ symptoms, I suspect more towards the input side of things.

Peter Wieck
Melrose Park, PA