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game king 17" 3902 board, was working ok last time i turned it on (a few weeks ago) now powered up, the touch screen not working,(monitor works ok but nothing works upon touch)  (touchscreen communication error displayed on screen), keying cpu with chip#22 cleared but didn't help, turned the jp key, calibrating never shows dots to touch. figured it was a t/screen controllerr so i swapped whole working monitor (from a good game king next to it)  still giving same error,  next tried swapping working board, and power supply.  good grounded outlet.  -the components i pulled off this machine work fine in another one.

so monitor ok, cpu board ok, and power supply ok,  but touchscreen still not working, what else? only thing left in machine is motherboard, and cable from monitor to motherboard -or did i overlook something simple?

It's to early today for a long story so will keep it short.

I had two machines with this problem ( at the same time )  and it was the same trace burned on the mother boards  both machines.  Soldered a jumper wire in and as for as I know they are still working.

Try unplugging the printer and see if the touchscreen error goes away. If that doesn't work try the I/O cards.

 talked to a tech in las vegas, i followed his suggestions,  also swapped motherboard and video cable,  still nothing.

after running out of things to try, he said to disconnected the bill validator.  (pulled it out) -touch screen error disappeared. slid the validator back in, it cycled and restarted. all is well -wtf?

seems that if the validator doesn't communicate properly with the netplex,  the netplex shuts down communication with everything

all is working now.

Netplex is a funny thing.

I would suggest disassembling the BV tray / housing and study closely the wires coming out of the back of the BV black port.  These wires are thin and frail and often the plastic coating gets frayed where they turn down up against the top sharp edge of the housing.  On a GK these wires typically lead to the right out of the port before they head down and get squished up against the metal housing when the BV is pushed in and pushes up against them.  When you pull the BV out it releases the pressure.  The problem you are having is often a result of one of these frayed wires getting pushed up against the metal housing and it grounds out the comm.

To Buzz, what trace did you hard-wire on the motherboards?

 

That was a long time ago.  :103- :103-  As I recall it was real close to the edge close to one of the large edge plugs. Was pretty easy to find, the trace on both boards was fried.

looks like the power for the touch screen controller runs through the motherboard through j-5.  (the red and black wires on end of plug) thinking if one was going to burn it would be one or both of them.

hello you first suguiero you change the CPU:
transistors Q7, Q8 2N3904 if you are out the same fault changes
the integrated U87, U86 are optocouplers and if that sige you mention the error coming from
Finally change the transistor Q4 is a 2N3904, so I repaired several communication error cards