Environment And Situation

• Control room of an apartment
• Number of installed product : 1 (PC-based NVR, dual-LAN supported)
• Remote support : O

Reported Issue

1. When the user connects LAN cables to both NIC on the product(one NIC is connected to a private network and the other one is connected to internet)simultaneously, internet is unreachable.
2. Monitor connection keeps disconnected after system booted. It happens in random minutes(mostly between 1~5) - The colleague in the site told me he's not sure whether it's just about monitor disconnection or the entire system down.

Diagnosis And Assumptions

• I asked to change the monitor but the monitor issue kept happening. -> The monitor was innocent.
• If it was the case that the entire system was down, it might be because of kernel panic. -> I needed to check kernel messages using dmesg and journalctl
• Every time the monitor issue happened, fans on the product started running faster.
• I was debugging via Anydesk, but when the monitor issue happened, Anydesk remote screen stopped.
• This site was where I'd already resolved other issues. But back then, there was no kind of this issue.

-> Suspicion on hardware(GPU or CPU heat problem, power supply issue, etc.)

-> Suspicion on environment(Based on the fact that the monitor issue was not there in the site back in the day) - The user might have connected other products on the same power strip

-> Suspicion on the product itself(hardware related malfunction caused by physical shock).

First Solution

-> Recall the product and check it in company.
-> After check the product in the company, send it to hardware vendor.

Second Diagnosis After Recall the Product

• The monitor issue didn't appear again.
• I checked the recording data -> !!Recording data was well!! == The system didn't go down entirely. It was almost surely about only VGA issue. -> The user might have connected other products on the same power strip or been about another electronic issue.

Final Conclusion

• VGA malfunction caused by electronic issue(site dependent)

Solution

About Network Issue

-> Even though I couldn't check the network issue properly, I was pretty sure that the issue was related to routing metric(similar issues happened multiple times in other sites)

Keep This in Mind

• When system related issue happens, check recording data first.
• Even if an electronic issue occurs, it does not necessarily affect the entire system. In this case, only VGA output appeared to be affected.

Additional Assumption

• VGA output might have been affected first because of its sensitivity to power-related issues(not verified)