This article briefly introduces a solution. When you encounter that the router cannot start normally, and the sys and pwr lights are always on, you can try this method, and it may solve the problem.
Background
Due to a sudden power failure, after an old msr3620 router was started, two of the three ports were off, and the sys light was always on. After several attempts, I found that sometimes it can start normally, that is, the sys light will flash after starting. But it is not very stable. After Baidu, some people said that it can be reset, but on this machine, there is no reset button. Considering that the pwr is normal and there is no abnormal sound, the probability of hardware failure is not high, so I plan to use the console port or the page to reset the system configuration.
Alternative solution
Since the connection to the console port was garbled in the previous boot state, it should be judged that the system did not start normally.
After shutting down, the console line has been connected to it. Unexpectedly, after booting up, the console can output content. It can be seen that the loading system is normal. After about 5 minutes, the system shows that the loading system is successful, and there is no error report!
Since I didn’t take a video, I took two photos for reference. Under normal circumstances, the PWR light should be on and the SYS light should be flashing. There are also some routers that have a light that keeps flashing green, which is normal.
After starting, check the previous configuration, all are there. At the same time, I also checked the CPU and memory usage, which is also normal.
Then, guess that when the console port is not connected, the system probably cannot be loaded normally, and only when the console port is connected, it can be loaded normally. Although it feels absurd, I still record it.
It will be put on the shelves later for testing and observation. The preliminary judgment should be that the power failure suddenly caused the bin file to be unable to be read normally, or the memory was occupied, etc., so that the system could not be loaded normally.
Due to the rush of time, no further testing was carried out. If there is a failure to load next time, because of the output of the console port, the cause of the error should be quickly judged.
Finally, it is recommended that when encountering a network device failure, you must first connect to the console port to avoid wasting time caused by human speculation. After all, in our business, sometimes solving problems is more urgent than analyzing the cause of the problem.