Have an issue with Stern Quicksilver, if i drop the middle right drop target, it accumulates points continuously until the 3 bank of targets resets.

Put the machine in switch test, and when i hit the middle right drop target switch (31), switch 23 also appears on the displays (which is one of the drops on the left bank of targets). They both share a brown yellow wire. I tested the diodes (in circuit on both sw 31 and sw 23, and both test good - and the same as the other diodes nearby. When i test sw 23 by itself in switch test, it only fires itself.

I also noticed that standup target sw 15 in swtich test also fires sw 7 (tilt) - but it doesn't tilt during a game. Interestingly, sw 15 also has a brown/yellow wire.

Any suggestions on where to from here - should i replace the diode on 31 even though it tests OK?

Even more bizarre is another guy is having exactly the same issue with a Meteor - Sw 31 is causing sw 23 to fire, as well as sw 7 occasionally!

Further info - i went into switch test then removed plugs J2 and J3, when jumping the appropriate row/column pins on J2, the problem disappeared - ie: confirming that it is a wiring/playfield issue, not an MPU issue.

Replaced diodes on all switches in the brown/yellow row under the playfield - no result. I didn't bother doing diodes in the cabinet switches (tilts), as i disconnected J3 which are those wires and the problem remains.

Also removed the brown/yellow wire from each under playfield switch one by one and the switch test still gives multiple hits of different switches each time (was trying to isolate it to a single switch).

Have inspected all those switches (7,15,23,31,39) with the brown/yellow wire that are firing multiple times when one is pressed, and can see no metal parts above or below the playfield around them! Starting to go nuts with this one as i don't know what to try next.

Am i heading down the wrong track just looking at the brown/yellow wire which is for row 7 - do i need to trace the corresponding column wires for each switch in that row?

OK, snipped both those caps, no change.

Further update. Even though i thought it was not MPU related (due to pulling J2 and jumping pins and it testing fine), i put in an Altek board from my Paragon, and it works fine!!!

So now an assuming its an MPU issue - i guess i will looking at J2 where the brown/yellow wire goes, but not really sure what i am looking for!

Unfortunately problem stayed when i did this...

Had some other suggestions that it could be a fault or ground short on the MPU, was told to lift one end of C25 on the MPU which is the one that the brown/yellow wire goes to after the header pins and resistor.

When i lift one end of this cap, the machine plays normally (ie: doesn't rack up points hen you drop target sw 31), HOWEVER, in switch test, sw 15 still triggers sw 7 as well (the others in that row all test fine).

Apparently C25 is 390 pf, i only had a 470pf available, and used it and it went back to the same issue with scores racking up when you drop the target sw31. Lifted the end of the cap again, and it plays fine.

Any other suggestions on what to look for or replace on the MPU?

Original MPU that has been repaired and it looks to be a pretty good job of cleaning up corrosion.

Problem solved! Replaced R40 (57k) and all is good.

Thanks for the help

I can't claim credit- someone on Aussie Arcade suggested i look for that - as well as someone in this tread. Basically i started tracing components back from the pin where that row of switches went to on the MPU

Excellent! Glad this helped someone else out as well