When I worked with the robotic systems at the General Motors Oshawa Truck Plant, I was told by one of the engineers that there was an open capacitor on the motherboard of a robot controller. I told the engineer that an open capacitor on the motherboard was not a possible error message. I checked the servo-on activation of the suspect robot and did not find a problem.
Later on, I received another complaint about the same robot. This time, I cycled the servo-on activation many times until I finally got a dual-channel supervision fault. The servo-on activation includes a 24V series circuit and a 0V series circuit. When both circuits do not make, this results in a dual-channel supervision fault, which I assumed the engineer somehow interpreted as an open capacitor.
I used a multi-meter to check the voltage across the monitoring contacts of the relays and contactors until I found a voltage drop. I cycled the servo-on activation a couple more times to see if that contact open was repetitive. Once I was sure that contact was the problem, I replaced the contactor. Then I repeated the servo-on activation testing many more times to see if another fail would happen.
The next time I saw that engineer, he asked if I had replaced the capacitor, and I told him that I had replaced a contactor. The engineer did not ask me for any details.
This entry was submitted by Glenn Aitchison and edited by Rob Spiegel.
Glenn Aitchison's first field service job was in 1987. Since then, he has worked in robotics, automotive, and industrial automation and machinery. He received his Certificates of Qualification as an Industrial Electrician and as an Industrial Mechanic (Millwright).
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