Measuring 12v does not rule out the ULN2803 at U20. All the output lines of U20 are pulled high to 12v through a 1k resistor. The ULN will pull that line down to 0v when it drives it and let the 1k resistor pull it back to 12v when it is not driven. I don't see a huge mark on the upper part of U20 , but that doesn't look like real physical damage. Do you have continuity between pin 9 of J207 and pin 11 of U20 (red line in pic).

I see corrosion on the battery post , any corrosion below it at all ? no matter how small? Pictures look clean except for a blue glow in one of the pics , but it looks like a camera reflection.

On the picture, ULN receives the signal for column 8 on pin 8, in yellow, outputs it to pin 11 , the red line. Both green marks are the power of the chip, which is far from the mark on the upper right. If you have a logic probe, you can verify easily both pins 8 and 11 of the ULN. You might be able to test it with a multimeter only but most meters don't react fast enough to really see a change, but some do. Analog ones would. These pins are constantly driven at a regular interval. The ULN inverts the signal as it drives the output. On pin 8 you should measure 0v until it receives a 5v pulse. On pin 11 you should measure 12V until it pulses to 0v quickly.

No reason to type more than as already been explained, just read this post:

https://pinside.com/pinball/forum/topic/terrybs-guide-to-logic-probes#post-2514877

Most likely U20 really is faulty. It's a very common part and should be fairly easy to change , especially when you don't care about salvaging the part, for the rookies cutting the pins and removing the chip, to then desolder each pin one a time by pulling them out yields the cleanest results. Rule of thumb , if you change an IC , install a socket.. It costs cents and can save headaches down the road.

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