S2000 Double Diamond Stuck at "Coin-in Jam" & "Close Door M" Errors

[rcjones]

UPDATE: took a closer look at replacement MPU and it appears to have arrived damaged. Working on getting replacement and will advise if this doesn't resolve!

Hello all!
First time poster here stuck at "Coin-in Jam" & "Close Door M" Errors on new to me S2000 Double Diamond 3 reel.

I've spent hours going through previous posts to troubleshoot and unsure where to go next based on steps taken so far. Any suggestions?

Here's where I'm at:
- Replaced what appeared to be defective 502 MPU board with refurbished+tested 504 and cleared the "Please close main door error"
- Machine now boots up with no alarm, reels spin, and sticks at "Coin-in Jam" & "Close Door M" Errors.
- Setup menu viewable pressing reset button or turning JP key, but unable to enter as buttons don't appear to work.
- All buttons are lit up
- Replaced door I/O board and still stuck at errors listed above
- Machine is setup for coin, BV and tickets, and error persists with these components unplugged.

Not sure what to try next and will gladly provide any further details required. Greatly appreciate any guidance this forum can offer.

Thank you!

RC