it would most likely be the big board you would need to change, check that all the contacts are ok on both ends of the loom (wiring) I would try changing the cash in and cah out meters first.
also ensure that the opto (the bit where the coins come out) on the hopper has no wires broken and the lens is clean. Check that the machine has been topped up and has coins in it. It is unlikely to be the hopper motor itself if it revolves without jamming, wd40 the motor won't hurt
try the little circuit board mentioned before, check that all the opto's on the reels are clean, clean em with some alcohol (not beer!) check that all the status lights on the mpu are lit (especially the 24v light - labelled) if not then check again the fuses in the power supply, they may look ok but meter them to make sure.
If all these check ok then you might need a new psu
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