I somehow messed up something on my MPU, and now can't seem to figure out what to do next. Any suggestions welcomed!
The short story is, I replaced the switch-stacks on my pop bumpers with all-new switches, and they weren't reacting properly. I was digging around in there to adjust them, and then while rolling a ball around to see how the pops reacted, I happened to notice that other switches on the playfield weren't functioning. Bottom row of switches is out.
Reading Pinwiki (http://techniek.flipperwinkel.nl/wms11/index3.htm#switch), I determined that I likely shorted the switch matrix to the 50V. Lesson learned, turn off the game before fiddling around with the switches. Ok.
I got some replacement ICs, along with sockets, and replaced U30, U39, and U38. U30 and U39, I got 4011s; U38, I got a W65C21N6TPG-14 from Great Plains, which they say is a direct replacement for 6821: https://www.greatplainselectronics.com/proddetail.asp?prod=W65C21N6TPG-14
Turning on the game, now, sometimes I get an awful squeal (that initial squelch when you turn the game on and everything's fine, but it doesn't stop...), but usually will just get a U38 PIA Failure notice.
I thought perhaps my soldering was bad, but I re-flowed all the solder at U38, and it all looks good. The IC looks to be seated properly. Still a U38 PIA Failure.
Did I blow something else up when it shorted?
How do I go about diagnosing what the problem is?
Thanks in advance.