testing Liftmaster garage door sensor with DVM

[Donald]

Has anyone used a DVM to test the sensors for Liftmater garage door openers. I know there is a diagnostic LED on the opener and lights on the sensors. I assume they put a DC voltage on the wire to power the sensors and push (or not push) AC voltage when the sensor detects something.

 

[Dan55]

Heres more info http://www.youtube.com/watch?v=GbmufXgpl14

 

[Dan55]

I just replaced mine a few weeks ago, the led started flickering and at first I thought it was the alignment. Did all kinds of troubleshooting and realized sensors are a weak spot. Not expensive to replace http://www.amazon.com/gp/product/B0006N1RH6/ref=oh_details_o00_s00_i00