Hi Guys,
Interesting fault.
It makes me wonder why the IR LED 'senders' would go faulty though? is there a design flaw and theyre running the wrong value current-limit resistor to the IR LED sender ???
LED's will work seemingly forever, and to see that a few machines are dropping LEDs smells like it'll happen again unless the fault truly cured.
The new leds may work now, and might even work all next year, but it may also be sloooowly frying away.
I'd love to see a circuit and see what's really going on in there 
Good Luck,
Marty.
Actually, LED's do not last forever. They usually start to get dull over time, then eventually die.
The transmitter (IR) LED's are on the whole time the machine is on, so they will eventually fail.
The circuit on a Williams/Bally pinball is 12V going through a 270ohm resistor, through the IR LED to ground... that's it.
