Sure looks like a power supply decoupling cap to me since there is a polarity mark on the largest component on the backside of the hash chip PCB (2 pin component).
Right - makes sense, thanks guys! I just assumed diode since it has the distinct polarity mark which diodes also have. But it seems a cap makes more sense in this part of the circuit.
I'm surprised your works without the cap in place, @Biffa! Then I'll see if I can get it working simply without that.
Would still be great to hear what component this is (specifications) so it can be replaced if it is missing or blows / melts like in that case.
One could de-solder it, test it, & determine it' value.
So if it screwed up it could be replaced.
PITA for sure, but . . .