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I work with a LTE modem. Normally when I plug it, ttyUSB0/ttyUSB1/ttyUSB2/ttyUSB3 appear. Suddenly it stops working and I don't know what happened. Why does it happen?

Thank you in advance

Update: more information about the modem

The modem even doesn't appear as usb detected (lsusb)

lsusb
Bus 001 Device 003: ID 0424:ec00 Standard Microsystems Corp. SMSC9512/9514 Fast Ethernet Adapter
Bus 001 Device 002: ID 0424:9514 Standard Microsystems Corp. SMC9514 Hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

Information dmesg:

dmesg | grep usb
[    0.070655] usbcore: registered new interface driver usbfs
[    0.070710] usbcore: registered new interface driver hub
[    0.070802] usbcore: registered new device driver usb
[    0.339993] usbcore: registered new interface driver lan78xx
[    0.340051] usbcore: registered new interface driver smsc95xx
[    0.367935] dwc_otg 3f980000.usb: base=(ptrval)
[    0.769196] dwc_otg 3f980000.usb: DWC OTG Controller
[    0.769229] dwc_otg 3f980000.usb: new USB bus registered, assigned bus number 1
[    0.769265] dwc_otg 3f980000.usb: irq 56, io mem 0x00000000
[    0.769581] usb usb1: New USB device found, idVendor=1d6b, idProduct=0002, bcdDevice= 4.19
[    0.769593] usb usb1: New USB device strings: Mfr=3, Product=2, SerialNumber=1
[    0.769602] usb usb1: Product: DWC OTG Controller
[    0.769612] usb usb1: Manufacturer: Linux 4.19.56-v7+ dwc_otg_hcd
[    0.769621] usb usb1: SerialNumber: 3f980000.usb
[    0.771222] usbcore: registered new interface driver usb-storage
[    0.775835] usbcore: registered new interface driver usbhid
[    0.775841] usbhid: USB HID core driver
[    1.191896] usb 1-1: new high-speed USB device number 2 using dwc_otg
[    1.432191] usb 1-1: New USB device found, idVendor=0424, idProduct=9514, bcdDevice= 2.00
[    1.432206] usb 1-1: New USB device strings: Mfr=0, Product=0, SerialNumber=0
[    1.751888] usb 1-1.1: new high-speed USB device number 3 using dwc_otg
[    1.882172] usb 1-1.1: New USB device found, idVendor=0424, idProduct=ec00, bcdDevice= 2.00
[    1.882186] usb 1-1.1: New USB device strings: Mfr=0, Product=0, SerialNumber=0
[    1.975380] smsc95xx 1-1.1:1.0 eth0: register 'smsc95xx' at usb-3f980000.usb-1.1, smsc95xx USB 2.0 Ethernet, 
b8:27:eb:8a:ea:fc
[    5.112990] usbcore: registered new interface driver brcmfmac
  • Include the relevant part of the dmesg log in your question. – Dmitry Grigoryev Jun 27 at 11:57
  • Many possible reasons: modem broken, usb socket broken, power supply broken, ... Try swap things to narrow down trouble making area. – tlfong01 Jun 27 at 11:57

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