Pinwiki has very good steps for diagnosing switch matrix issues, try to follow those steps.

First determine whether it is a board issue or play field issue by following their steps.

Do the jumper test between the column & row connectors as described on pinwiki:

http://pinwiki.com/wiki/index.php?title=Williams_WPC#Switch_Problems

4.20.3 Switch Matrix Problems

Isolate the problem to the MPU or to the game wiring/diodes/switches

Do you have a logic probe?

Hmm, since it is not detecting any column strobes on J209-9 then I guess you should test for continuity from pin 8 on U19 to that pin. Look at the diagram on pinwiki, there is a diode D10 and resistor R65 along that path.

I tried jumpering to that pin on mine and switches on the bottom row closed.

Getting beyond my skill to help... pinballrehab.com has some instructions on testing using a logic probe when an entire row is out. Might want to start a new topic to get more experienced help!

I have all the old boulders, previous owner replaced mine with a new set. I'll check at home whether that one is in good shape & let you know.

I tried to fix my ball hangups last night. I have the rubber on the VUK wireform and pushed the Cliffy up against the ramp so there is no ridge. Sadly I am still getting ball hangups. The reason is that the ball guide and ramp edge don't line up so the ball hangs up against the edge of the ball guide.

Has anyone bent the ball guide to fix this? Looks like 2-3 mm would fix it.

I have decided to drill another hole in the ball guide mounting tab beside the existing hole. This will shift the ball guide a few mm and in my tests eliminates ball hangups. I'll drill & reinstall tonight.

Spent a few hours disassembling the upper playfield area where the ball infamously gets stuck. I filled the lower ball guide hole with epoxy filler and re-drilled a new hole, so now the ball guide and ramp line up. My ramp and cliffy line up so there is no gap between them on the bottom. Still, I had the ball get stuck!

For me, it just sits near the end of the plastic ramp. Not on the gap. That spot is pretty much flat left-to-right so it just seems to hang up there if it loses momentum.

I'm going to add another little rubber to the VUK to see if that reduces the number of slow balls that get hung up. I've got a rubber on the left side now.

Any other ideas? Almost like I need to make a little bump-out in that area so it'll roll either left or right rather than just park there.

Switches require different force depending on the model of switch. Wonder if it was replaced with a higher force one.

Long thread about different switch options here: https://pinside.com/pinball/forum/topic/cherry-microswitches-in-wms-games

Pinball Life even has some original Cherry switches: https://www.pinballlife.com/da3-switch-body.html

I'm a noob at this but was able to recreate the flashlamp speaker panel board for my #BSD using KiCad off a scan of the original board and some caliper work. Made the lamp holes a little tight but otherwise it was perfect. HEP even used one in his latest restore!

Super cheap to have made too! I did mine at https://jlcpcb.com

Noticed Bigfoot's head was moving slowly then got a 'bigfoot error'. Looked at Bi-Directional Motor Drive Board for Bally/Williams Machines - A-15680/A-14768 and C2 had failed and leaked electrolyte on the board.

Removed impacted components and cleaned and scraped traces with a fibreglass pen. Minimal trace damage thankfully. Covered up the scraped traces with conformal coating from a bottle.

Got to try out my Hakko FR-301 desoldering gun -- WORTH IT. Put in a socket for the LM339. I ended up cutting the pins with a little fine-toothed saw as part of the removal, maybe a Dremel with a cut-off wheel would work better.

A few bucks in parts from digikey and I'm back in business, working well. Ordered a backup board just in case.