Hi everyone,

I probably have done something that was not very sensible: on an otherwise working STTNG I was fixing a problem with the left return lane sensor, and I raised the playfield with the machine switched on (I did remove all the balls before doing so). Because of the nature of the problem I was fixing I had the machine in test mode with the switch matrix displayed on the screen. While I was raising the playfield, I noticed that all of a sudden almost all switches in the matrix went from a large square to a single dot.

After I was done and lowered the playfield, none of switches in columns 3, 4 and 6 registered anymore, with the exception of switch 68 (shooter): that still worked. According to the Operations Manual, this corresponds to all optos. Looking at the ball through opto board (which I believe is a redesigned replacement), I didn't see any LEDs that were lit. The same goes for the opto board under the playfield: its LED was not lit. I tried triggering some optos (e.g. the cannons), and nothing registered.

I made a picture of the switch matrix afterwards. There were no balls in the machine when the picture was made.

What would be the best approach in trying to troubleshoot this?

IMG_20191224_115450 (resized).jpg

I did check the fuses... or at least I thought I did. I probably missed one, because when I checked again I indeed found the 12V fuse to be blown. After replacing it all optos were fine again, so thanks for your suggestion!