KC868-A16S GSM/LTE Connection Issue - CSQ=99 (No Signal)

[vardan]

Problem Summary
I cannot get network registration on my KC868-A16S board. The modem consistently returns CSQ=99 (No Signal) and fails to attach to GPRS.
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Hardware Setup
• Board: KC868-A16S (ESP32 with integrated GSM module)
• SIM Card: Active SIM with data plan (tested working in phone)
• Antenna: LTE antenna connected to the antenna port
• Power: 12V DC power supply

Software Configuration
Platform
• PlatformIO with Arduino framework
• ESP32 Dev Module target
• TinyGSM library v0.11.7
Pin Configuration (from our code)
// GSM Module Pins
#define PIN_GSM_RX 32  // ESP32 receives from modem
#define PIN_GSM_TX 33  // ESP32 sends to modem
#define PIN_GSM_PWR 23 // Power pin (unused currently)
APN Settings
#define APN_NAME "internet"
#define APN_USER ""
#define APN_PASS ""
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Initialization Code
// GSM Modem Init
SerialAT.begin(115200, SERIAL_8N1, PIN_GSM_RX, PIN_GSM_TX);
delay(3000);
Serial.println("Initializing GSM modem...");
modem.restart();
// Check Signal Quality
int csq = modem.getSignalQuality();
Serial.print("Signal Quality (CSQ): ");
Serial.println(csq);
// Wait for Network
if (!modem.waitForNetwork(15000)) {
    Serial.println("Network registration FAILED");
} else {
    Serial.println("Network OK");
    // Connect to GPRS
    if (!modem.gprsConnect(APN_NAME, APN_USER, APN_PASS)) {
        Serial.println("GPRS Connect failed");
    }
}
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Serial Monitor Output
Initializing GSM modem...
Signal Quality (CSQ): 99
Waiting for network... FAILED (will retry in loop)
Network lost. Reconnecting...
Network unreachable
CSQ=99 means "Not Detectable" according to AT command specifications.
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What I Have Tried
1. ✅ Verified SIM card works in mobile phone
2. ✅ Tried different APN names ("internet", "")
3. ✅ Checked antenna connection
4. ✅ Tried baud rates: 9600, 57600, 115200
5. ✅ Power cycled the board multiple times
6. ❓ Not sure if there is a PWR_KEY or RESET pin that needs toggling
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Questions for KinCony Team
1. What is the GSM module model on the A16S? (SIM7600, SIM800L, A7670C, or other?)
2. Are the TX/RX pins correct? (We use GPIO 32 for RX, GPIO 33 for TX)
3. Is there a power-on sequence required? Does the GSM module have a PWR_KEY or RESET pin that must be toggled before use?
4. What baud rate should we use? (Currently 115200)
5. Do you have a working demo code or .bin file that we can flash to verify the hardware works?
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Additional Information
• Wi-Fi connection works perfectly on the same board
• All other I2C devices (PCF8574, RTC, sensors) work correctly
• The board was purchased recently and appears undamaged
Thank you for your help!

[admin]

1: A16S pcb can connect with SIM800L 2G or SIM7600E 4G module.
2:
GSM:
RXD:GPIO15
TXD:GPIO13
here is ESP32 pin define for A16S: https://www.kincony.com/forum/showthread.php?tid=2788
3: if use our GSM module, not need to use PWR_KEY.
4: SIM7600E: 115200
5: if you use by SIM7600E, you can download KCS v2 firmware directly to use it. Just SIM800L not support KCS v2. if you are using SIM800L, i suggest you use serial monitor to test AT command.