I have pulled both boards out either side of the trough, and reflowed all soldering.  This did not fix the problem (ie: still shooting two balls at startup).

I then pulled each board out of my working indy and swapped them one at a time across to STTNG, neither fixed the problem.  So from this i assume the problem is definitely not the boards themselves.

I have also read that the trough itself can become a bit pitted where the balls sit, causing them to roll slowly to the upkicker coil.  I chocked one side of the machine to make it slope more and the balls roll down no worries.

From this i assume the problem is elsewhere, i see from the switch matrix, this column goes to pin 13 of U20 - could u20 be stuffed???

the only other bit of relevant info i can pass on is that this only occurred after the machine was shifted across a couple of metres.

Help please