I realize there are quite a few posts on modern Stern machines ejecting two balls. Before you jump me, please read everything I've done so far and you should understand why I'm posting for help. At this point I'm desperate and would try anything. Before anyone asks, yes I only have four brand new balls installed.
The issue: Every once and while two balls will be ejected instead of one. It's random and after hours of testing I find no pattern as to when and why it will happen.
What I observe: Diagnostics reports all trough switches, optics, and shooter lane switch working properly even after thorough testing. The clear function also has a nice visual that also confirms this as I test. Most testing is done using the clear function as I can reproduce the issue faster this way.
What I've test/tried:
First thing I did was replace both the transmitter and receiver optics, no luck. Next I took a multimeter and tested the resistors and transistors on the receiver board to make sure they were reading right (switch on or off). I then continued to test the soldered leads that the wires connect to, the harness itself, up and up all the way to the board. On the board itself it reads correctly from the optics on or off.
The next thing I tried was adjusting coil power. Soft doesn't eject balls and there is no difference in behavior between normal and hard.
Then I adjusted the leg levelers to make sure things were dialed in correctly and they were.
In an effort to try to reproduce the issue consistently and perhaps eliminate some root causes I tried the following:
Catching the ball before it hits the shooter lane switch. - Does not change behavior or cause behavior.
Causing the ball to bounce back into the ejector. - Does not change behavior or cause behavior.
Tilting the table (the table does not have plumb line installed) to make it easier to eject. - Does not change behavior or cause behavior.
Tilting the table to make it harder to eject. - Does not change behavior or cause behavior.
Adding an extra ball. - Causes the behavior everytime there are five or more balls in trough.
If anyone has any ideas of where to look next I'm all ears. Trough switches seem to work fine, but then again I'm not sure how to test them with the multimeter so if anyone can explain that to me I can always try that. Thanks!