bang on playfield with ball in shooter lane and look for phantom switch closures?

run the switch test to look for stuck switches?

Does it show any visor targets scoring when it scores points ?

It doesn't require a stuck switch for phantom switch closures to occur (would be easier if it did). Typically switch wired wrong, reversed diode, shorted diode or diode lead touching switch lead.

Did you do any work on any of the switches during your project?

Remove all of the balls from the game and raise any drop targets then see if the problem persists.

In order to get a phantom switch indication the following has to happen: Three switches closed and then the fourth indicates closed even though it isn't. These four switches will form a rectangle on the switch matrix. Since at the moment we only know two of the switches (and they're in the same row) we need to find at least one of other two switches (thus why we want to open all switches and test). The other two switches will likely be in the same row as each other, but not in the same row as the two switches you've identified.

A long answer to say the other two switches can be almost anywhere. Take the balls out, raise the drop targets and test again. That should tell us something.

Did you do any switch work?

Also make sure that when you close the credit button that the 5 right bank middle is the only other switch that closes. If the entire row closes then there is a different problem than phantom switch closures.

All of the testing should be done in switch levels test.

On System 11 you have to wait patiently to get the full list of closed switches.

I would presume any other switch in row 3 will also have the same issue. Also, when you go into switch test do you get any errors (specifically ground row short error)?

Remove the row and column connectors after going in to switch test. Jumper from row 3 to any column and see if only the one switch shows closed or you get multiple closures. This will narrow it down to the playfield or the board.

http://www.pinwiki.com/wiki/index.php?title=Williams_System_9_-_11#Switch_problems

Maybe the 1000 points is a clue. How many switches score exactly 1000 points at that point in the game?

Go through the switch matrix test that rob identified...remove the two connectors from the mpu for the row and column. Using a short jumper of wire and with the game in switch test, start jumpering pin one of the row to each pin of the column one at a time. The display should register one switch only. Follow along with the switch matrix chart in your manual. Then move to pin 2 of the row and again jumper to each column pin one at a time. Then pin 3 and so on. If more than one switch shows up during this test for each jumper combination then you have a board issue. If not then you have a shorted diode in the pf.

Yes it means the issue is in the playfield...so shorted diode likely.

Since the problem only happens when you close the switch that would indicate there is a short to ground between the switch and the diode (or possibly the column side of the diode). If the short was on the row side of the switch you would get a ground short error in switch test.

Since none of the other switches in that row cause a similar problem I would highly suspect the credit button as the problem. You should also check if any other switches in that column cause a similar problem with their row.

After that I would check all switches in that column, and then all of them. You're looking for a reversed/shorted diode, diode lead touching a lug on the switch, diode lead or lug touching ground, etc. The short always seems to be at a position where you can't see it so I just slightly arrange all leads for maximum clearance as I go through the switches.

Narrowing down the problem is a reasonable approach. You can split the daisy-chain in half on the same row (or column) as the credit button. This would eliminate half of the switches, and then proceed based on the results.

It would take some re-wiring, but there is another approach: swap the rows and columns. You can't just swap the plugs, but would have to wire up an adapter cable. If you put the column lines on the rows and the row lines on the columns then none of the switches would work because of the blocking diode. You then go through and press every switch and if one indicates closed then that switch is your problem.

I don't want to speak out of school, but I'll PM someone who may have an adapter for sale that will do the above switching of rows and columns. I forgot the board is just for WPC at the moment.

Don't forget to check if any other switches in the same column cause that issue on other rows.

In that case I would start narrowing down the problem as I described above.

Or you can just make sure that you are always 'player 1'

I'm kind of revisiting my thoughts on where your issue is. It's really not acting like a phantom switch closure issue so let's try some other things before tearing stuff apart (although everything still points at the credit button).

Test continuity from column 1 to ground (game off) and see what you get.

When you did this are you sure you waited long enough to see if additional switches would be listed?

Do you have a logic probe?

This may not be your issue, but I was getting phantom points on my xmen when I shot the ball. Turned out to be coming from the sling shots. The gap on one of the leaf switches was to small, and the vibration of the kicker caused points to be awarded.

That's a problem. Disconnect IJ8 and test from the grn/brn wire to ground.

Yes it is. Could be a pinched wire, but most of the time the diode lead or a lug on the switch is touching ground. Only 8 to check now.

Check the Plumb Bob and Roll Tilts. They're grounded and metal and if the switch is grounded to the switch mount, then it makes its way through the plumb bracket or roll tilt to ground. I had a Getaway once where the switch was grounded to the habitrail. Everytime someone shook the machine, the PF bounced around enough that the habitrail grazed the hinge bolt on the side of the cabinet which was grounded. So from switch, through metal habitrail, to bolt head to ground. That was a fun one to find.

The fix is always simple, it's the troubleshooting that can be a bitch. Glad you got it working.

Good job