Hi Marty and Beaky, thanks for the replies.

Beaky, there are no LED's lighting up on the MPU. I checked for continuity on the plug and I'm pretty sure the circuit is not complete (I used the lowest resistance setting because I don't think my multimeter reads continuity). There was no change in the reading when I flicked the switch and I compared this to another machine which did change. So that means there is a problem with the power lead, the varistors, the fuse or the filter itself, right? The fuse is definitely OK, Can I test the other components?

yep you sure can. it is possibly the power filter.  again you will need to have the plug disconnected from the supply to do the following tests.

unplug the plug between the switch under the pinball machine and the transformer. then check resistance from the brown wire going in to the fuse holder to the brown wire connected to on your 3 pin mains plug and then test the blue wire on the filter to the blue wire on the plug.

if all is ok (0 ohms on each) then test from the brown wire going into the fuse holder to the orange wire coming out of the fuse holder. if this reads 0 ohms then proceed to the next step. if not then there is a problem with the fuse or fuse holder.

next test from the orange wire coming out of the fuse holder to the orange wire going into the line filter,

if this is 0 ohms check the orange wire going into the line filter to the black wire coming out of the line filter. then test the blue wire going in to the line filter to the white wire coming out of the line filter.
if all is ok (0 ohms) then proceed to the next step. if not then it is the line filter that is faulty.

next test the black wire coming out of the line filter to the black wire on the plug that connects to the transformer that you disconnected earlier. if it is open and does not read 0 ohms then try changing the position of the switch if it is ok then do the same with the white wire coming from the line filter.

let me know how you go.

at no stage during these tests is the machine to be plugged into the wall