Price drop!
$6200

Okay good...your voltages are checked out ok.... Hmm

Turn OFF the power to the machine.
Earlier Qbert  pointed out the corrosion to the MPU board.
I'm concerned about that as well.
That machine at some point in its lifetime, was horribly neglected/stored in a VERY damp place.
We need to try to determine if we can solve the Netplex down message before sending out the MPU for repairs.
Member Lookes is very good at repairing MPU's that have acid damage from leaking Varta batteries.... that big green one that used to be on the board...someone removed it at some point.

A little bit of history...did you see this MPU working before?
When did the Netplex messages start popping up?

FYI Netplex devices are the printer, progressive displays, topbox LCD computers, and bill acceptors (BV or BA)
One can disconnect them one at a time to find out what's causing the error, but you also get messages that they're not connected, and you have to be able to disable/enable the Netplex device, so you don't get that error.
That's harder for you to do right now.
Let's try simpler things.... with the power OFF, slide out the I/O card on the door panel for the button deck.
It's located just behind the top of the panel looking at it with the door opened.
If you look at it, it's in there on an angle.
I just want you to tug on the metal handle...pull it up about an inch, then slide it back down firm re-seating it onto the pins.
The Molex plug that's connected to it in the handle hole is rather difficult to get off....you don't need to remove it as you're only pulling up on the I/O card one inch so you can re-seat it back down.

You might have another I/O card on the side of the MPU enclosure.
Go ahead and slide that out an inch towards you and firmly re-seat it back into the socket.
I don't want you take them out all the way...you don't need to.
All we're doing is re-seating them....why? Because sometimes a pin or two gets oxidized...sort of like a car battery terminal from the 80's.
The oxidization creates a film of non-conductive junk....so pulling the circuit card off and pushing it back on kind of rubs the oxidization off of the pins and promotes better electrical contact.

I need to point out that a machine "getting stuck initializing" could also be software having bent chip legs folded underneath its own chip body.
When that happens, it's hard to see whether or not the chip is actually fully inserted all the way down into the socket holes.
The only way to check those is to carefully, slowly remove each chip one at a time out of the sockets and re-insert them back in making sure each leg goes all the way down into the socket holes.

Thank you never saw one with this type of low jackpot numbers on a 5 line dd

That is a $1 encoder guide. IKE silver dollar

 

The mystery is solved!

The backside of that coin head looks pretty big, I believe it was still a dollar denom??

That's where I am leaning toward.