It doesn't seem like a sound issue. If it's not scoring then its not registering the event in the first place. check the switch contacts, etc.

A good place to start for information on your game is here:

https://www.ipdb.org/search.pl?any=flash+williams&sortby=name&search=Search+Database&searchtype=quick#871

To find schematics: You need to verify which MPU board you have as it may have been upgraded from the original, then look on that site for games that were originally built for that board.

You can try the built-in diagnostics (see owners manual) and run the switch test. Those diagnostics are not the best, but they may tell you something.

If you still can't get anywhere, you can try these test ROMs: http://pincoder.reversion.ca You will need access to a chip programmer and a chip, but they are
much better tests and could help you find the problem quicker.

Start with the switches and wiring though, and then check that you have good power going to the MPU board. This is also a good source of information: http://www.flippers.info/system6repairpart4.asp

It applies to a system 6 board, but there are still lots of good bits to get you started. Flash was manufactured with a system 4 board, but it is possible to upgrade to 6 and 7. They're all quite similar in how they are built.

Hope this helps

On the DRIVER BOARD (lower board, hanging off the MPU board), there are two 9-pin connectors on the upper right side.

The weight of the wiring harness usually cracks the solder joints on the back of these connectors

https://pinside.com/pinball/forum/topic/vids-guide-to-bulletproofing-williams-system-6

6bdf8d3b1946b13a0fb4bc72634b870092f7568c (resized).jpg

The backbox is an oven.

As it heats up, the boards expand

Use a magnifying glass, the cracks in the solder may be much smaller than the picture, could just be a hairline **ring** around the pin.

Remember also, that the pins might be or originals that are 40 years old. Those had a 25 insertion cycle rating, so by now they could be grey and worn out, rather than bright and shiny.

New pins will be square, old ones round

Even worse than a loop, they are in an 8x8 matrix. So a problem in one row can affect a switch in another. Sometimes you have a whole row or column out = 8 switches not responding.