A few "pro" tips for IR ball sensors

[LegoTekFan486]

In my case it was the early 2000s model of Alley Roller (by Ice Ball) but there's enough games with IR sensors these days (and as it turns out, from an earlier period than I realized) that these should apply to all of them.

• If the IR sensor would normally be obscured from extraneous light, bright lights in the room (or sunlight from a window) may confuse such sensors, when you have the playfield up or the covers off. So if you're chasing a sensor error that magically goes away and then comes back, see if casting your (literal) shadow on the sensor makes a difference.
• On some games, there is a visible indicator LED on the receiver end of the sensor. This *usually* aids in troubleshooting, but in my case, somehow the motherboard was registering the sensor as "beam blocked" while the visible LED was *off* and that threw me for quite a while.
• Some games may also interpret "too much" IR on the receiver as a broken sensor (open or shorted depending on the design of the "sensor board") see my above comment about extraneous light affecting the sensor, when the playfield is up.

I was chasing sensor errors (which the game would "scroll" through on its own) that just didn't seem to be yielding to any troubleshooting method I could think of. Pointing fans or hair dryers at things, leaving my meter on it while the machine stayed on to see what voltage was drifting beyond spec (something was affecting all sensors)

It was the sunlight through the garage door, which I couldn't really close because it would then be too hot and dark in the storage unit (it was possible to open from inside and there was power in there, but no overhead light)

I finally clued in when an error message went away just by me standing in a specific position to move my meter - but I hadn't *touched* literally anything, even the wires between the head and the lane.

I was frankly a bit embarrassed at first that it took me that long to find it. But the machines are now functional, and hopefully I saved at least one person a frustrating "loop" of chasing an intermittent problem.

P.S. : I have seen this with VCRs as well, they may think they're at the end of the tape and not play with the cover off, if external light is shining on it at exactly the wrong angle (for an IR sensor, sunlight or an incandescent light may matter more than a LED or fluorescent, but it depends on the design)