I'm having an issue with what I believe is trough switch #4 in a Stern SAM. During gameplay, a ball will drain but the trough switch won't register and the game will do an endless ball search rather than advance to the next ball.
I have tested the trough switches in the Diagnostic mode of the Service Menu and they check out fine. I tested them by loading four balls into the trough and then, through the open coin door, using a small screw driver to gently move the balls onto and then off of their respective switches. There is a narrow slot in the trough which allows access for this purpose. Why would the switch check out when tested but for some reason not alert the game to the presence of a ball in the trough? Do I replace the switch to begin with? Below is a link to the only trough switch I could find at Pinball Life. Marco does have a few more, but none that truly matches the Stern switch in my trough.

https://www.pinballlife.com/data-eastsegastern-ball-trough-microswitch.html
IMG_0545 (resized).jpg

Thanks, Schudel.
I amended my post to reflect how I tested the switch using balls, not my finger.
Failing opto board? I hadn't though of that, but the game is low-play HUO, so I would not suspect a failed board. Can the Diagnostic menu be used to evaluate an opto board? If not, now about a mult-meter? Such testing is nothing I've ever done before.

Thanks, Erik.
I loaded new balls in the game just today. They roll in the trough normally. No sluggish movement due to magnetization. Heck, I even have my magnets turned off.
Still, knowing there are no opto switches in my trough is helpful. I was wondering if there might be one at the entrance to the trough as I was sure the switches *in* the trough were simple, mechanical micro switches.

Thank you, too, Thermionic.