You would think so.. I have written some test ROMs from scratch, you could try them on the bench but they were designed to run in the game. Give them a try and see if they help you find what the problem in the flipper is.

You can download them from here: http://pincoder.reversion.ca

There is also a thread on this site where you can leave some feedback: https://pinside.com/pinball/forum/topic/new-williams-system-6-in-game-test-roms

Let me know how you make out!

I'd try the suspect PIAs in a different known good game. My experience with the used pulls 6821s you pay around $1usd each and expect around 10% to be dead on arrival bad and another 2% has infant mortality. If every single one works with the test rom but acts up in a real game you probably have some other kind of problem.

Leon test is not full proof but it should discover most bad PIAs. Some kind of logical issue could slip through as leon's test rom uses no special patterns when controlling the output ports. Just flips all the bits at the same time.

W65C21N should be fine (at $6usd or so) but they mention in the data sheet... "The W65C21N is plug replacement of NMOS and CMOS 6521 and 6821 devices with current limiting resistors". I don't think current limiting resistors are needed in any pinball application, but something to keep in mind.

There’s a reason why they were named p.i.a.

The past Russia ones seem mostly ok. Think 1 in 10 a dud! There should be more used good ones available from USA or Canada. With the Ultimate MPU, many of us no longer spend hours working on old Bally & Stern boards from 1978-1982. Same with 5101 ram. Times are changing towards replacing boards instead of working on them.