What game? If it’s a classic Bally it could be an intermittently shorting capacitor.

disconnect all caps on that daisy chain . its a switch matrix issue most likely. dealt with it plenty.
install new caps if needed.
can also go in switch test see if a switch is closed in the matrix column or row associated with tilt.

I think he meant that on that entire line of switches (row or columns) , there are more caps and they should all be removed.

Also check all the diodes while you are in there.

If not a cap problem, then I would guess you have a shorted diode on the single drop target or one of the upper flippers (the switch that triggers the sound effect).

If this is the case, the game is tilting occasionally when the right pop bumper is hit.

There is also a tilt switch on the bottom of the playfield that is often overlooked. Make sure that is not misadjusted. Without delving too deep into the matrix, check the coin door for stuck coin switches. They can cause issues like this when the right combinations of targets are down and hit.

Using the rectangle switch theory, three switches have to be closed for the signal to flow through a shorted (or bypassed) diode and end up on the wrong return line. Since it's a single ball game, there are no balls sitting on trough switches and because there's no way one ball could hit three switches simultaneously, the only other switches that could be closed are drop targets and the flipper sound effect switches.

Drawing the rectangle as you did, you can see the 3-bank of drops in the same column as the tilt switch. Any one of those could be a corner. The only other drop target, as well as the flipper sound effect switches are all in the far right column. One of them would be another corner. So the final corner would be in the far right column and same row as the tilt switch, which is the right pop bumper.

I'm confused, though, how you found the problem to be the rebound switch. The way the theory works, whatever switch is on the opposite corner of the phantom switch will be the one with the shorted diode.

These problems are usually tied to stuck coin switches because they are not shown in the playfield matrix schematic, you have to pencil them in, and they do not have diodes so nothing stops the signal from going backward through them.

When trouble shooting a switch matrix read it like a road map. In this case you need to travel from ST0 to I6 and tilt bridge is out. So how do you detour and get there easily? Start on St0 and travel up to one of the knocked down drop targets. Go through that to the corresponding coin switch which you penciled in. There is no diode on the coin switch to stop you from passing through backwards to St1 and down to the clone chamber target. In this more likely scenario a stuck coin switch will tilt the game if you have the drop target down and you hit the clone target.

We've inherited this problem from Basement Facts .

We have narrowed the problem to be either the A or C drop target switches. If either are closed, the right pop bumber will tilt the machine.

We picked this up yesterday. We have since repinned the connector to the mpu, scanned reverse side of the playfield, and everything tests ok in switch test. Nothing looks out of the ordinary. We've also tested all the diodes in circuit with the switch closed and they all test within expected ranges.

I am guessing we'll have pull diodes in the rectangle to see if we can get any further.

What I dont understand is why drop target "B" does not cause the issue.

Any help would be appreciated.

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When you draw the boxes linking all the switches in the matrix regarding the issue, the switches opposite to the tilt switch with reference to those two drop targets are the two upper flipper switches. Maybe someones wired both those flipper switches wrong by forgetting to add the diodes and left the switches normally closed.

Agree upper flipper switches are suspect. Even if they have diodes, if the diodes are installed on the wrong lugs, or the wires aren't attached properly, you'll get problems like this. Neither of those switches should have wires soldered to the banded end of a diode. That's an easy thing to check.

If the right pop bumper has a factory looking cap, I would replace that and probably the diode too.

Speaking of diodes, I've had one that looked perfect until I desoldered one leg to replace it, and the leg just fell out of the diode. So, even if it looks good, it might be fried. I usually just clip them out and replace even on the possibility of a problem. It's cheap and quick.

I actually suspected the upper flippers after reviewing the matrix diagram. I didnt have a paper diagram and was using my phone (I'm old school).

This machine is in one of my neighbor's garage. Here is the picture he took of the upper flipper switch, I beleive the right side.

received_3427245550730429 (resized).jpeg

The diode is soldered directly across the two wires which is wrong. See the extra lug with the cut diode lead? and the lug with the two yellow-red wires have remnants of the other cut diode leg.

Here is a different view.

received_287336272382975 (resized).jpeg

The pictures don't clearly show how the switch is stacked, but it looks to me this is how the diode should be wired:

SpaceInvaders_FlipperSwitch.jpg

The pictures are lousy. The left side flippers have been rebuilt and there is no place to include a diode. Good thing is it playing now however we have no flipper sound.

This image is the correct wiring of the diode.

The diode is currently reversed in the machine which means it will block the strobe signal instead of allowing it to pass through when the switch is closed. Also, because it’s backwards and connected to the return wire directly, the switch doesn’t even have to be closed for the signal to pass through the wrong direction and cause a tilt when the pop bumper is hit.

My guess is when someone did flipper work they installed the diode in the proper orientation, but connected it to the return wire instead of the switch tab (or in your case in lieu of a switch tab). I assume it would continually make the flipper sound so they just reversed the diode.

Guy said he wired this way intentionally because it was only way to get sound from flippers. The pictures, first off, are the best to illustrate, but the is a post with no wiring that banded side goes to. I'll try to better pics.

The tab needs to be isolated from the switch blades. If it is, move the yellow/red wires and the non-banded end of the diode to the tab. The white wire should be alone on one switch blade and the banded end of the diode should be alone on the other switch blade.

We got this issue resolved. We reversed the diode and the new EOS switch did not have a blank stud. We put the loose leg on the switch mounting screw. Resolved the problems in the switch matrix.