1.Check Whether the screen or controller is working or not;
2.Check whether the SIM card is overdue;
3.Check that the SIM card is oxidized resulting in bad connect;
As shown in the figure below, SIM card quality is poor, especially in the outdoor, moisture is more, easy to be oxidized
If possible, customers are advised to use SIM cards with high gold-plated quantity or industrial grade SIM cards, as shown on the right of the figure below
4.Check whether the SIM card can access the Internet, you can plug the SIM card into the phone to check whether it can access the Internet.
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Huidu Asynchronous LED Controller