Yeah...that's an old drawing I made...lol
I can't remember the last time I've used actual door optics.
Try these troubleshooting notes below...>>>
How to diagnose a netplex link down error.
First disconnect all netplex drvices except the vfd.
This includes the bill acceptor, printer, some progressive displays, some top box bonus devices.
Now that those are disconnected check the following.
Is your error solid or blinking.
Blinking
Do you have a 50x or 1270 mpu?
1270
Remove the varta and u16.
50x
Mpu fault.
Solid
Do you get no disp on your credit display
No
The mpu is not booting check the mpu for signs of faults or problems with the chips.
Yes
Check voltage at the vfd on the 2 pin connector
Check the data cable for any signs of damage especially where the door closes.
Mpu is faulty or damaged check for bent pins.