I am replacing some old brown emitter bulbs on the little opto boards in my STTNG with new ones from Pinball Life -
https://www.pinballlife.com/williamsbally-led-transmitter-emitter-for-opto-assemblies.html
and just wondering, before I solder them in, if these bulbs are polarized? Wouldn't have occurred to me but then the little boards are marked with an "A"node side and a "K"athode side and I don't want to do this incorrectly.
Yes both sides are polarized. For the LED transmitter side the longer lead is anode (positive) and the shorter lead with the flattened edge of the LED bead is kathode (neg).
The receiver side is basically a transistor where the infrared LED light turns it on. The longer lead is typically the emitter. The shorter edge is the collector. And the light is the base. I would double check the datasheet as the receiver side pinout can actually vary. I got burned once assuming the polarity dot on a SMT photo transistor was always the emitter.
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Yes, bare LEDs are always polarized. For a regular/standard-size LED, the longer lead is the anode side, and the flattened side is the cathode.
Of course, the LEDs already in the board are presumably mounted correctly, so you should be able to just match up the new LED's flat side with the old LED's orientation.
Boy-o-boy am I glad I posted about this! Never noticed the longer lead and the flattened edge until you guys pointed them out. And I thought it was gonna be a dumb question. Thanks so much!
I also notice that every little opto board has a dab of what looks like rubber cement between the board and the bulb. Was this to hold the bulb in position while soldering, or it is to mitigate the vibrations of the solenoids firing?
Quoted from jibmums:I also notice that every little opto board has a dab of what looks like rubber cement between the board and the bulb. Was this to hold the bulb in position while soldering, or it is to mitigate the vibrations of the solenoids firing?
Probably some of both. These boards are often mounted in a place that gets abused with vibrations and its critical to be pointing the right way. Bent over ceramic disc or cockeyed typical transistor not the end of the world, but an opto not perfectly oriented could cause an issue.
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