Quoted from jimy_speedt:
I have the exact same problem, at the same period, with a TZ and Dr who.
One row and one column on the SM are lit (squares) in test mode. I replaced the Dr who CPU with a new one, no change.
When the pin is on, if I remove the 4 SM connectorson the CPU (205, 206, 208, 212), the switch matrix in test mode does no longer show any square, I deduct the CPU is good.
When the machine is off, I remove the same 4 connectors, at boot it tells me check fuses f114, f115.
I received and read the litterature about the voltage sent by the driver to the CPU, my 12v is ok on Tp3 and 5vdc ok on TP2.
Some very focused support (no general articles or comment) would be helpful .
Thanks a lot in advance
If removing the connector shows all boxes off then the MPU is good.
Column 7 being mostly on is CORRECT, this holds true for most WPC era machines, as those are all opto switches are are normally closed instead on normally open when at rest.
Any opto switch will show as closed in test. The check fuse message is because you removed the connector, and all the optos went open, and that (never correct) error message shows since the machine thinks there is no 12 Volts to any opto since they are all open, and thus it "must just be a fuse". Ignore this message.
The real problem is a ground short on Row 2, somewhere you've shorted the white-red wire to ground, or a diode has blown. REMOVE ANY MODS YOU HAVE RECENTLY MADE, especially lighting or switch bling. Look at all switches in ROW 2, find a backwards diode or short to ground.
Attached is a switch matrix for Dr. Who.
Again COLUMN 7 is normal, there is NO DIRECT PROBLEM with COLUMN 7, OPTOs are NORMALLY CLOSED. This also applies to any other switch with the word OPTO in it for WPC era machines. It will show lit when it is working correctly.
But, since there is a switch in column 7 on row 2, it may still be the source or your row 2 issue.