Printer or scales lose communication: how to fix COM and USB ports

Trade automation expert at Torgsoft

Instructions for hard fixing ports and drivers in Windows. Use this if, after rebooting or reconnecting equipment, the port changes and the Torgsoft program loses connection.

These instructions involve changing Windows system settings, drivers, COM ports, power-saving parameters, and in some cases GPO policies, so they should be followed carefully. Incorrectly changing the port number, blocking the wrong driver, or applying an unsuccessful device installation restriction policy may result in a complete loss of connection with the equipment. Before making changes, we recommend recording the current device names, port numbers, and driver versions. If you are not sure which driver or port is currently working, it is better not to change them at random and to contact your system administrator or technical support.

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When ports and drivers need to be fixed

After restarting the computer or server.
After updating Windows or drivers.
When working with USB-COM adapters.
When working through Remote Desktop (RDP).
If a lot of USB equipment is used.

How to understand that the problem is in ports or drivers

In Torgsoft, there is an error «Port not found» or «Device unavailable».
The printer in Windows creates duplicates: «Copy 1», «Copy 2».
The COM port number changes by itself (it was COM3 → became COM5).
Printing or scale reading works only after reconnecting the cable.

Why Windows changes ports or loses the device

Changing the socket: Windows binds settings to a specific USB port.
Dynamic IP: the network device address has changed.
Updates: Windows automatically replaced the stable driver with a newer one (incompatible).
Power saving: the system turns off power to USB ports or puts the computer to sleep.

How to fix ports and stabilize the connection

1. Physical fixing of the USB port (Basic)

Rule: one device — always the same USB socket.
Mark the cable and the port with a colored marker.
Avoid passive USB hubs (without a power supply).
If possible, connect critical equipment (fiscal registrar, scanner) to the motherboard ports (rear of the PC).

2. Disabling USB power saving and computer sleep mode

To prevent the ports and the PC itself from "falling asleep":

Control Panel → Power Options (Control Panel → Power Options).
Next to the active plan, click Change plan settings (Change plan settings).
Disable sleep mode: in the line «Put the computer to sleep» (Put the computer to sleep), select the value «Never» (Never).
Disable USB power saving: then click Change advanced power settings (Change advanced power settings). Expand the USB settings branch (USB settings) → USB selective suspend setting (USB selective suspend setting). Set the value to: Disabled (Disabled).

3. Hard fixing of the COM port number (for scales and scanners)

To solve the problem of spontaneous COM port changes:

Open Device Manager.
Find the section Ports (COM and LPT) / Ports (COM & LPT).
Right-click the required device (for example, USB Serial Port) and select Properties.
Go to the Port Settings tab and click the Advanced... button.
In the COM Port Number field, explicitly select the required free port (for example, COM3) and click OK. From now on, Windows will try to always reserve this number for this device.

4. Fixing the IP address (for network devices)

If the device is connected via LAN/Wi-Fi:

Log in to the router settings.
Find the DHCP Reservation section (Address Reservation).
Assign the current IP address to the MAC address of the device.
In Windows, in the printer port properties, specify a Standard TCP/IP Port with this IP address (avoid using WSD-type ports).

5. Blocking driver updates (via GPO)

If Windows forcibly updates the driver and breaks printing or communication with the scales:

Device Manager (Device Manager) → Device Properties (Properties) → Details (Details) → Hardware Ids (Hardware Ids). Copy the ID.
Press Win + R, enter gpedit.msc.
Path: Computer Configuration (Computer Configuration) → Administrative Templates (Administrative Templates) → System (System) → Device Installation (Device Installation) → Device Installation Restrictions (Device Installation Restrictions).
Enable the policy «Prevent installation of devices that match any of these device IDs» (Prevent installation of devices that match any of these device IDs).
Click the "Show..." button and paste the copied ID into the list.

6. Stable drivers and LPR (for RDP)

For Chinese printers (Xprinter, Gprinter), use old stable drivers (for example, Seagull version 2018.x), not the newest ones.
For Remote Desktop (RDP), configure printing via the LPD Print Service (locally) + LPR Port (on the server) to avoid problems with port redirection through EasyPrint.

How to check that the connection with the device is stable

Restart the PC.
Launch Torgsoft, without changing the settings.
Print a test receipt or weigh an item.
If the equipment worked immediately — the ports were fixed successfully.

What is important to remember

If the equipment "drops off", the problem is almost always USB power saving, a change of the physical port, or automatic driver updates. Always fix this at the Windows level before changing settings in Torgsoft.

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