Start by checking your 12VR at TP3 of the power driver, its right next to F115. If that checks out, you will want to verify your 12V is also good on the CPU board.

https://www.pinwiki.com/wiki/index.php?title=Williams_WPC#Check_fuses_F114_and_F115_message

That is very odd...it's like you have no 12VU to the playfield, but I know you have 12VU on the PDB since you have a working display. I can also tell the switch matrix appears to be working at least in part as the always closed SW, SW24 (Column2, and Row4) is reporting correctly; this makes me want to rule out the 12V to the processor; If I really wanted to check it, I would check across U20 pins 8 and 9, but yours are going to be under that battery board making it harder to access.

Usually is a contact failure on the panel underside the playfield. If your led is not dimming on it check the connection.

In my experience with this, its the cap at C2. If the cap has never been replaced, its very likely it has leaked and caused some corrosion.

I'm familiar with this type of failure, there is a actually another topic opened today where I believe that to be the case, however I see no indications of that type of problem here. The picture of this part of the PDB isn't the best quality, but IMO its good enough to see a lack of discoloration you would see in the presence of corrosion. A close inspection of this area would let you know for sure but with a functioning SW24 you know for sure that U20 is generating at least 1 column pulse for column 2 and it's being read back through the LM339 for Row4.

That being said, I do replace this capacitor whenever I have one of these old power boards on my bench as a preventative measure if there are no signs that it was replaced.

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LED1 is on so you have 12V. You must get back this voltage at J116/117/118. If the result is right your 12V is disappear between backbox and opt board.

If the cap is original, i would replace regardless. I wouldntn

I wish I took a pic of my last c2 repair. Pulled cap and it had just started leaking. Couldn't tell from either side of the board. Stayed under the cap.

You need to get a meter and test some voltages. You have the connector that should be plugged into J118 plugged into the splitter that powers the color dmd and also plugs into J116. That's ok as J116 and J118 put out the same voltages, but J116, J117 and J118 is where you want to start. You're looking for 12V dc on pin 2 of each of those connectors.

If you get 12V on each of those pins, you need to test your opto board for 12V. Manual will show you which pin carries the 12V.