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(Topic ID: 272678)

Opto transmitters blowing [Solved]

By SunMonkeyAZ

3 months ago

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  • 8 posts
  • 3 Pinsiders participating
  • Latest reply 3 months ago by SunMonkeyAZ
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257A1575-BB31-4676-9B4F-75B144C80B3B (resized).jpeg

#1 3 months ago

Have had some weirdness with optos lately on an NBAFB and narrowed down to 7-opto board. Ordered a replacement, installed today. Went into switch edge test and one ramp opto wasn’t working. #7 on the board. No glow on the transmitter with camera. All others ok (5 in trough #1-5 on board and #6 another ramp). Thought maybe new board had an issue or maybe opto just gave up. It happens. So I flip-flopped with the other ramp opto set that’s on #6 since they have molex connectors so easy to swap to see if it followed transmitter or stayed with #7 location. After turning back on neither worked at either location. Like being on #7 blew them. All the trough optos transmitters are 1.4v but these two are 12v measuring at transmitters. Don't know if that is normal. Receivers work with flashlight test. So now I have two dead optos. Grabbing some more tomorrow locally but worried what will happen. Put old board in and measurements are all the same. With the old board all optos worked but was getting phantom closures. Not sure what I can check to make sure everything is ok before connecting and blowing more out.

#2 3 months ago

The transmitter side should have 12V.
Make sure the high watt current limiting resistor is doing its job.

Chris Hibler - CARGPB #31
Http:// - The new place for pinball repair info

#3 3 months ago

The transmitters are powered by 12v, but the voltage is dropped to about 1.4v by the 270 ohm resistors R15-21. If somehow your new board was somehow fitted with the wrong value resistor in any of R15-21 it could result in damage to the opto transmitter. Once you measure 12v directly across an opto transmitter you know the transmitter is bad, has to be.

#4 3 months ago

OK. This afternoon after work I will check the R21 resistor tied into #7 since it's the problem one and compare to the other 6. If it reads different I can trying taking one from my old board.

#5 3 months ago

Tested resistors and R21 was showing a short, no resistance. All the others were around 270. So figured bad resistor. Removed it to put in one from my old board but checked resistor off board and it was fine 270-ish. Checked and had continuity between the two pads for the resistor with it out. Turns out the pad was touching the trace for the 12v so both sides of the resistor were connected to the same 12v source so transmitter was getting the voltage with no resistor in line. Peeled back the pad so it wasn’t making contact but had to still put on the old resistor from my older board since I cut the leads on what I that was the bad new one. Replaced the transmitters and tested good now.

257A1575-BB31-4676-9B4F-75B144C80B3B (resized).jpeg
#6 3 months ago

Good job on your repair, and thanks for letting us know what it was.

#7 3 months ago

Nice job. Is that an OEM board or an aftermarket?

Chris Hibler - CARGPB #31
Http:// - The new place for pinball repair info

#8 3 months ago

Aftermarket. I notified where I bought it so they are aware in case there are others and it’s a design or manufacturing issue. But hopefully just one of those odd things that happens and not a recurring problem.

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