Error Appeared After Thunderstorm: Connection Shaken Loose

Errors on a system with no history of trouble at all, appearing gradually over a period rather than suddenly. Both units are clean and undamaged inside. Nobody has touched the wiring since the day it went in.

Trouble that arrives gradually on undisturbed equipment fits something loosening rather than something failing. Boards fail at a moment; screws loosen across years. The connector blocks at both ends carry every signal the system depends on, and checking them means opening a cover and applying a screwdriver. That takes minutes and costs nothing in parts, which is why it belongs well before any consideration of the electronics inside.

Terminal screws are tightened once and then left alone for the life of the installation. A running system vibrates continuously and heats and cools every single day, and both of those work against the fixing over years. Eventually contact pressure drops far enough that the signal becomes unreliable, while the connection still looks entirely normal to anyone who inspects it by eye. Nothing has failed and nothing needs replacing. One screw has backed off a fraction, and that is the whole of it.

Every terminal at both ends is checked and retightened, not just the one that had backed off. All of them went in together and have taken the same years of vibration since, so the rest sit at much the same point. This is the cheapest and most productive routine work available on a system, and it gets skipped almost everywhere.