Cheers, nothing stands out on a first look.
Use the playfield schematic I posted above, it has the correct wire colors listed.
Quoted from wawhite92025:What I don't understand is how the MPU can show switch numbers 1, 3, 5 for three of the drop targets when there are no such switch numbers?
The switch test mode on these early Stern/Bally games is flawed, it only displays the lowest number closed switch. i.e. when you press that left outlane switch, because of your particular fault you're not seeing the game telling you that it's also seeing switches #40, #32, #24, #16 as well as #8 being closed. So when you press that left outlane switch all these other switches I just mentioned are being seen as closed aswell. This is a phantom effect with your fault and how switch matrix's work. This is the reason I asked if you could run the switch test mode and press the switches in reverse order of the switch ID numbers listed in the manual.
The switch matrix is made up of columns and rows. Referencing the matrix picture above, when the game wants to read the switches, it first raises strobe #4 line from zero to 5 volts. It then reads all the eight switch return lines at the same time. Any of the switches on those return lines that are closed with respect to strobe #4 will report 5 volts, open switches will report zero volts.
Strobe #4 is then released back to zero volts and then strobe #3 is raised from zero to 5 volts. Again all the eight return lines are read at the same time. Any of the switches on those return lines that are closed with respect to strobe #3 will report 5 volts, open switches will report zero volts.
Ditto strobe #2, #1 and then #0.
The diodes on all switches is what separates the return line signals from the strobe lines to prevent phantom reads.
Now in your scenario, all the wrong switch readings you're getting are coming from the strobe #3 line (white-yellow wire).
The errors you're getting suggest the strobe #3 is shorted to something. The moment you close a switch on strobe #3 the switch return line is getting stuck such that it's reported as closed on every strobe line read.
But this doesn't explain why two switches on that strobe #3 line are apparently ok (drop targets B and D). Can you confirm this?
BTW, when you're pressing switches with your hand, make sure no other part of you body is touching ground.
Can you comment on the below:
left drops b.jpg