Where are you checking your 5V rail? At TP1 or at the chips themselves?

Make sure you have 5V at pin 8 U9 etc.

Reason i say this is that after TP1 there are a whole array of ceramic caps - one of these goes down and you will not get the logic voltage to the chips or TP5, but it will read at TP1

I measure 5 volts at TP1 and TP5 and pin 8 on U9.

I have just swapped C14 and C15 (470pf capacitor) with some i de soldered off another board this did not work either, LED still stuck on.

must be U16 (9602) or U15(MC3459L or 74S37) anyone got both of these chips for sale PLEASE.

Ian