That's usually a netplex issue. The way you diagnose that is you remove one netplex device one at a time until you find the offending part. (Printer and validator are netplex devices as is progressive displays and coin-in hardware).
So I did get the machine this weekend and here is what I know.
The former owner swapped out the old 19 pin Kortek LCD screen which he gave me to a 25 pin Wells Gardner door mount LCD. He said once he swapped out the LCD is when all the error messages started.
I did what you said and stared unplugging devices. The printer was already unplugged and so I went for the Bill Val and booted up with the same error. On the touch screen it has a microtouch 3m box that has a flashing green light. When you touch the screen it turns solid so I can only assume that it knows the screen is getting touched.
Last night I went Frankenstein on the old monitor and took out the guts and swapped the machine back to the 19 pin.
I took a power cord from my personal computer to give the Wells power.
I took the old touch board and hooked it up but didn't connect the cable from the monitor because it wasn't the same plug but the old touch board did turn green upon booting.
I took the VGA connector from the 19 and connected to the Wells and booted it up.
All same error messages.
My ram clear came today and did that and still no response from the touch.
When you do the touch screen calibration on it the screen says to press the dot on the screen but no dot every shows up.
So with my Frankenstein move last night is it safe to say that the Wells monitor is good and that he may have done something wrong which caused damage to the MPU or Backplane?
I do have replacement MPU and Backplane coming to swap out.
My gut is telling me bad MPU...
Thoughts?