This may be related to my last question in which I thought soldering temperature damaged the module.
About my first prototype with an HL7800-M module. Firmware is latest 126.96.36.199. I have 3 SIM cards from the same M2M sim card company. Two of the cards worked and connected immediately. AT+COPS reported the operator T-Mobile. A 3rd card for some reason connects though AT&T, and takes up to a minute before it decides to connect.
I just built 2 new HL7800-M prototypes on a new PCB version. All the relevant wiring is the same. Firmware is latest 188.8.131.52. Suddenly the 2 cards that had worked do not connect. The 3rd SIM that reported as AT&T still delays before connecting, but AT+COPS now says the operator is name of the SIM card vendor instead of AT&T as before.
I have an RF probe connected to an oscilloscope with which I can tell when the module transmits. With the 2 similar SIMs the HL7800 never transmits. Apparently these SIMs never attempt to connect. AT+COPS? result 0 (not searching).
I know the hardware is working because with the 3rd SIM there is a big transmit signal when it eventually decides to connect. Both of the new prototypes work similarly with all SIMs. Unfortunately I cannot compare to the first prototype because I used those parts for one of the second prototypes. See my last post " HL-7800 Easily Damaged By Soldering?" They may not have been damaged by soldering. They just stopped working with the 2 SIMs.
I have a TELIT cellular module UE866 in which all SIMs still connect immediately and COPS still shows the original AT&T and T-MOBILE operators. So I don’t think there is anything wrong with the SIMs.
Debug initialization output seems the same between working and non working SIMs. One thing I don’t understand is at the end of initialization there is always a line or two of “[CRI] Fail to send At respond”.
Output of some commands:
+KBNDCFG: 0,0000000000000A0A188E+KBNDCFG: 1,0+KBNDCFG: 2,0
After the 3rd SIM connects this command result shows a band: