Abstract: Disconnection faults in the control circuit of 10 kV switchgear can easily cause circuit breakers to fail to trip or close, seriously threatening power grid security and power supply reliability. Taking the VS1 type withdrawable circuit breaker as the research object, this paper analyzes the principle of control circuit disconnection, identifies major causes such as damage to trip and closing coils, abnormalities in the spring charging circuit, auxiliary switch faults, and loose wiring, and proposes a systematic troubleshooting method that proceeds from external to internal components in descending order of fault probability. In addition, a convenient measuring point selection scheme based on PCB wiring is provided, offering technical support for maintenance personnel to rapidly handle faults.