IGT Game King Coin-In issue

[Saurkraut]

New member here, first I would like to say the amount of knowledge on this forum is remarkable. It is amazing to see such a community here helping everyone out with any problems they might have.
Backstory- My wife and I purchased two machines for my parents, who like to frequent the casino but isn't the easiest for them at their age anymore. One of them, Wild Taxi IGT Game King, is giving me more grey hairs daily... After having for about 2 months the MPU back-up battery died. As a mechanic I didn't realize the complexity I was about to dive into...  I have a great general understanding of electronics and how things "work", but this rabbit hole is deep and I'm at the point of throwing parts at it just to see if I can get it working again.
I pulled the MPU (power off), replaced the battery, and then found out I need a "magic" key chip to be able to set up the machine again since I basically fully wiped all settings popping that battery out. I ordered the 22 chip and thought we are good to go as soon as I set up the machine again. I was wrong, this machine was set up with a Tito Home 3 so I also had to find those settings for printless/no coin transactions. (thank you forum for understanding this  ) So now I'm stuck at a Coin in error after my reset. I have replaced both of my I/O boards (used/tested good), checked wiring connections, looked for any board damage, and following the breadcrumbs here my next step was going to reach out to Jim @ Midwest Slots to replace my 3902 MPU board. Maybe it shorted somehow? Aside from replacing all of the guts of this machine I'm kind of at a loss here. Thought I'd post this because I'm defiantly a noobie to this hobby and any help would be greatly appreciated.
Attached are pics of the board (incase I'm wrong with the 3902) and the error.
Thank you in advance

[Tilt]

Take a real close look at U74 on the MPU board.  It's going to be under the soundcard next to one of the long white connectors that the soundcard plugs into.  See if there's any signs of discoloration, a crack, bubble, or any other signs of damage on it.  If you've already replaced the I/O cards the MPU is probably the cause assuming of course that the machine worked fine before the battery died.

[Saurkraut]

Thanks for the reply! I don’t see anything apparent on the chip but I’m out of other solutions… I might be just ordering a board from Jim.
Just got off the phone with sixcardmark (big thank you by the way) who just verified my Tito setup and we both are stumped haha
I can’t upload right from my phone so I will post a picture when I get home.

[Tilt]

Ok.  There's not always visible damage when it goes bad, but often there is.  It's normally accompanied by a Meter's Disconnected error message too, but again, not always.  Get a new MPU from Jim and hopefully that gets it back up and running again.

[Saurkraut]

Here is that pic, tried to get as close as possible without distortion

[Tilt]

Nice picture!  No signs of damage there. 

Is yours a coinless machine?

[Saurkraut]

This is a coinless machine, yes.

[Tilt]

Do you have an optics bypass plug like this on the wiring harness inside your door?

[Saurkraut]

My jumper isn't as pretty as yours but it should still do the same thing.

[Tilt]

Ok, well that was the last thing I could think of before trying a new MPU.  Some game software has a coinless setup option that will let you run the game without that jumper being in place.  I was thinking that maybe yours did and after the battery replacement you needed to re-enable that option, but with the jumper in place it wouldn't matter if it was on or off. 

[Saurkraut]

I did see that option in some of the other posts/videos I have seen in the key options menu but my machine doesn't have that. I'm not opposed to replacing the MPU just making sure I'm not missing anything else it could be. I really appreciate your input in this matter, I will follow up once I have a new board installed and fingers crossed it solves my issue.

[Saurkraut]

Update: Just swapped everything into the new MPU board, keyed, and coin in error is gone! Big thanks Tilt, Mark, and Jim I really appreciate the help figuring out this error.

[Tilt]

Glad you were able to get it up and running again     Thanks for posting the solution to your problem!