Black Horse F2304 8-Channel Output Module – Single Channel Stuck ON Due to Shorted Output Transistor (H50 System) - Excellent PLC

Fault Scenario

During system operation, the F2304 module exhibited the following abnormal behavior:

Output channel 5 remained ON continuously
Command from controller: LOW
LED indicator for channel 5: constantly ON
Downstream actuator energized continuously, creating safety hazard
Other channels functioned normally

Symptoms indicated internal output transistor short rather than command or wiring error.

Step 1 – Verify Input Signal

Controller output for channel 5: LOW
Voltage at input terminal: 0V → correct
Other channels respond normally

Inference: Module is receiving correct command; fault is internal.

Step 2 – Measure Output Terminal

OUTPUT_MEASUREMENT:

Measure DC voltage at channel 5 output terminal.

Compare with other functional channels.

Check for abnormal current draw.

Findings:

Terminal voltage: 24V regardless of command
Current: higher than rated for the load → confirms shorted transistor

Step 3 – Module Diagnostics

Engineering software reports: Channel 5 Driver Fault – Overcurrent
Self-test confirms output transistor failed in closed state
Other channels unaffected

Observation: Fault is localized to a single output driver.

Step 4 – Corrective Action

Immediately power down module to prevent actuator damage
Replace F2304 module with a spare
After replacement:
- Channel 5 output responds correctly
- LED reflects command state
- Actuator operates as expected
Optional repair: replace output transistor (advanced repair, requires calibration)

Step 5 – Preventive Recommendations

Avoid exceeding channel current rating
Inspect wiring for short circuits that may stress outputs
Conduct functional tests regularly
Keep spare F2304 modules available for rapid replacement

Engineering Insight

F2304 output transistors are wear-sensitive under high-load or shorted conditions
Single-channel short does not affect remaining outputs but poses safety risk
Early detection prevents equipment damage and downtime

Conclusion:

If a channel on a Black Horse F2304 8-channel output module is stuck ON despite correct command, the cause is likely a shorted output transistor. Replacement restores safe operation in H50 systems.