A7670E (LILYGO T-SIM-A7670E) cannot establish GPRS or TCP connection

[ollio]

Environment

• Board: LILYGO T-SIM-A7670E (ESP32)
• Modem: SIMCom A7670E-LNXY-UBL
• Library: TinyGSM (official, v0.12.x)
• APN: sensor.net (1NCE IoT SIM, private VPN)
• Firmware: AT+CGMR → A7670E_LNXY_UBL (no embedded IP stack)
• Connection target: TCP server at 10.64.0.2:8000 (reachable over VPN)

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Minimal reproducible example

#define TINY_GSM_MODEM_A7670
#include <TinyGsmClient.h>

#define MODEM_BAUDRATE 115200
#define MODEM_TX_PIN 26
#define MODEM_RX_PIN 27
#define BOARD_PWRKEY_PIN 4
#define BOARD_POWERON_PIN 12
#define SerialAT Serial1

TinyGsm modem(SerialAT);
TinyGsmClient client(modem);

void setup() {
  Serial.begin(115200);
  delay(1000);

  pinMode(BOARD_POWERON_PIN, OUTPUT);
  digitalWrite(BOARD_POWERON_PIN, HIGH);
  pinMode(BOARD_PWRKEY_PIN, OUTPUT);
  digitalWrite(BOARD_PWRKEY_PIN, HIGH);
  delay(500);
  digitalWrite(BOARD_PWRKEY_PIN, LOW);
  delay(5000);

  SerialAT.begin(MODEM_BAUDRATE, SERIAL_8N1, MODEM_RX_PIN, MODEM_TX_PIN);

  if (!modem.restart()) Serial.println("Modem failed");
  if (!modem.waitForNetwork()) Serial.println("No network");

  if (!modem.ping("10.64.0.2")) Serial.println("Ping failed");
  if (!modem.gprsConnect("sensor.net", "", "")) Serial.println("GPRS failed");

  if (client.connect("10.64.0.2", 8000))
    client.println("{\"signal\":\"GO_LEFT\"}");
  else
    Serial.println("TCP connect failed");
}

void loop() {}

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Observed behaviour

• The modem registers to LTE network (+CEREG: 0,5)
• modem.gprsConnect() always fails
• client.connect() → TCP connect failed
• AT commands such as AT+NETOPEN, AT+IPINIT, AT+CIPOPEN, and AT+CIPRXGET=1 return ERROR

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Expected behaviour

• The modem should establish a data connection via APN sensor.net
• A TCP socket connection to the given IP/port should succeed
• The examples like HTTPClient, MQTTClient from the TinyGSM_Fork lib should work

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Additional notes

• I have tried to update the firmware like suggested in the documentation, but the flash tool fails and the firmware is still the old version.

Thanks for maintaining TinyGSM – this board is becoming popular, and I’d be happy to test any fixes or patches.