I know this is a bit of an old post - but wanted to say thanks to the OP for posting his problem and solution. I bought a MPU327 in December for my Firepower and its been fine until last week when the top left pop would lock on when I started a game. Turned out to be a bad 7408 at IC8. Not sure why it decided to let go as I hadn't been under the hood messing around, but it's good to go now.
New! Dark mode!
Browsing Pinside at night? Getting tired of all the white? Switch to dark mode using the button in the top right (or CTRL-B)!