WPC board here.

I had to do rework on a new WPC CPU board.
Symptom one: no dmd display.
After scoping the board, I found a broken trace to one of the pads.
(Here I had to scrape the coating off to make connection.)
IMG_0001[1] (resized).JPG
Symptom two: lamps and coils erratic operation.
I changed a buffer IC and had no results...
I found out it was many cold solder joints to the output connector.
IMG_0002[1] (resized).JPG
The test game kind of worked but went haywire...
I had to reflow the solder to the CPU,RAM,EPROM, and ASIC and a few resistors.
Finally, got the board to function.

I would not be harsh on @Pinball_Basement; Nobody is perfect.
It was just a repair I got stuck doing...
The board came from a game that got smoked from to many
Like connectors that got switched around...
At first, I did not know if the severe board shorts blew up the new CPU; It did not.
It was just a bunch of little mishaps that I thought I would share.
In all, with this one repair, I really blame Williams electronics for having to many
like pinned connectors close to one another that allowed this stupid mishap to happen.
There's nothing like a game that comes into a repair shop with gremlins...
Each game has it's own personality, and traumatic life history.

Start small:
I would inquirer for a used solder wave bath machine or the table top version.
The CPU board is the most critical board to do correctly.

With the new regulator, you need to add a few boards to stress the +5 volts.
Then, adjust the regulator. The voltage drops on the WPC system going through all the IDC connectors.

From a place I worked at, the wave solder machine had a preheating area that brought the
whole pcb up to a certain temperature before the solder chamber... then cooling chamber...