Two of the three relay boards worked as expected immediately after installation. Other reviewers had similar issues. I checked the signal paths with an oscilloscope and noticed that two pins are shorted due to a solder jumper on the bottom of the board. After I scraped off the solder jumper with a small screwdriver, the board worked as it should. I would have given 5 stars if it wasn't for the post production quality control. I would buy again.
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