Right then have new components arrive today, the circuit will not power up without it and problem now is which way round should it go?

if i was to just bridge it it would be closed circuit. I'm now thinking the diode is part of clamping circuit maybe? if this was the case then the negative side of the diode would need to go to the negative side of circuit?

It does not make sense to just have a diode across the power lines as a protection circuit right? am i missing something here? wish i had a circuit diagram. The board won't clean up enough for me to see the tracks either