100203

Check Key Physical Condition

Inspect the channel switchover key on MCP for mechanical damage, stuck position, or loose connections.

Ensure machine is in STOP mode before inspecting control panel components.

Test Key Electrical Continuity

Use multimeter to check electrical continuity through switchover key contacts in all positions.

Check voltage levels at key contacts - should match specifications in electrical diagrams.

Verify MCP Connection

Check cable connections between MCP and NCU, focusing on channel switchover signal lines.

Look for loose X122 connector on NCU which carries MCP signals.

Replace Switchover Key

If key is defective, replace with genuine Siemens part maintaining proper wiring sequence.

Power down system completely before replacing MCP components.

Check Channel Count Parameter

Navigate to HMI > Commissioning > Machine Data and verify MD10000 $MN_MM_NUM_CHANNELS matches actual system configuration.

This parameter must match the number of physical channels configured in your system.

Verify Channel Names

Check MD10001 $MN_CHANNEL_NAME array to ensure all configured channels have valid names assigned.

Channel names must be unique and follow Siemens naming conventions.

Validate Channel Assignment

Review MD10002 $MN_CHAN_ASSIGN_TAB to confirm proper channel-to-axis assignment mapping.

Incorrect channel assignments can cause axis conflicts and safety issues.

Reset and Reload Parameters

After corrections, perform NCK reset via HMI > Commissioning > Reset > NCK Reset to activate changes.

Always backup machine data before making parameter changes.

Check Digital Input Status

Navigate to HMI > Diagnostics > Hardware > Digital Inputs and monitor switchover key input signals in real-time.

Input signals should change state cleanly when key is operated.

Verify Input Assignment

Check MD11210 $MN_EXTERN_CHAN_SYNC_M_NO_FCT to ensure correct digital input assignment for channel switchover function.

This parameter links physical inputs to channel management functions.

Test Input Card Functionality

Use forced I/O function in HMI > Diagnostics > PLC to test individual input points on the card.

Only force I/O signals when machine is in safe state and axes are disabled.

Check Signal Interference

Inspect input signal cables for electromagnetic interference sources and proper shielding.

Keep input signal cables separated from power cables and use proper cable routing.

Review PLC Channel Logic

Open STEP 7 and examine PLC program blocks handling channel switchover, particularly DB21.DBX system interface signals.

Look for DB21.DBX1.6 (channel switchover request) and related handshake signals.

Check Interface Signal Status

Monitor PLC-NCK interface signals in HMI > Diagnostics > PLC > Interface Signals during switchover attempts.

Verify proper handshake sequence between PLC and NCK for channel commands.

Validate Channel Selection Logic

Test PLC logic for proper channel number encoding and transmission to NCK via interface variables.

Ensure channel numbers sent to NCK match configured channel indices.