When a CNC vertical lathe fails, systematic fault diagnosis and repair are required. Here are the general repair steps:

1. Observation of fault phenomena: First, record the fault phenomena, including the specific circumstances of the fault, frequency, and whether there are abnormal sounds or vibrations. This helps narrow down the scope of the problem.

2. Check the electrical system: Check the electrical system of the CNC vertical lathe, including power supply, cables, switches, etc. Make sure the electrical connections are OK, there are no shorts or breaks, and check to see if any electrical components are damaged.

3. Check the hydraulic system: If the CNC vertical lathe uses a hydraulic system, check the oil level and quality of the hydraulic oil. Check hydraulic lines, valves and pumps to make sure there are no leaks or blockages.

4. Check the mechanical system: Check the mechanical system of the CNC vertical lathe, including guide rails, screws, bearings and other components. Observe for unusual wear, looseness or damage.

5. Check the control system: Check the control unit, programming equipment, sensors, etc. of the CNC system. Make sure the CNC program is correct and has no syntax errors. Check the working status of the sensor to ensure that it can correctly sense the status of the machine tool.

6. Diagnose the display and communication system: If the CNC vertical lathe has a display screen or communication module, check the connection and working status of these systems. Make sure the display is normal and communication is smooth.

7. Fault code analysis: If the CNC system provides a fault code, analyze it by consulting the fault code manual. Fault codes usually provide information about the cause and solution of the problem.

8. Equipment manual reference: Refer to the equipment manual of the CNC vertical lathe to find solutions to common faults. Manuals often contain detailed instructions for repairs and troubleshooting.

9. Professional maintenance: If the above steps cannot solve the problem, you may need to contact the manufacturer's technical support or professional maintenance personnel for more in-depth fault diagnosis and repair.

When performing maintenance, ensure that relevant safety operating procedures are followed and appropriate protective measures are taken according to the specific situation. If the operator does not have the repair skills, it is best to have the repair work performed by an experienced professional.