Applicable Systems
PSR-TRISAFE
Symptoms
The controller power supply has failed. The OK LED is off and the controller does not respond to communication attempts. All outputs are de-energized.
Possible Causes
- Power supply input voltage outside the rated range (20.4-28.8V DC)
- Power supply output overloaded by too many I/O modules
- Power supply internal fuse blown after a short circuit on the output bus
- Power supply component failure from age or thermal stress
Troubleshooting Steps
- Step 1: Measure the input voltage at the power supply terminals
Voltage should be 24V DC +/-10%; if outside this range, investigate the source - Step 2: Disconnect all I/O modules and measure the power supply output voltage
If voltage returns to normal, an I/O module short is overloading the supply - Step 3: Reconnect modules one at a time, monitoring the output voltage
The module that causes the voltage to drop is the faulty one - Step 4: If the output remains low with no load, the power supply is defective
Replace the power supply with an OEM-equivalent unit
How to Reset
Reset: After the power supply is replaced or the overload is removed, the controller restarts automatically when input power is restored.
Common Replacement Parts
- Power supply: 24V DC, 5-10A output (Match to controller power requirement)
- Power supply fuse: Fast-acting, 5A, 5x20mm (Match to existing fuse rating)
- I/O module: Digital or analog (Test each module with a bench power supply)
Frequently Asked Questions
- Q: How do I size a controller power supply?
Sum the current draw of all modules and the controller base. Add 25% margin. For a typical system: controller 0.5A + 8 modules x 0.15A = 1.7A; use a 2.5A supply.
- Q: What causes power supply failure?
Overload, input voltage spikes, thermal stress from poor ventilation, and aging of electrolytic capacitors are the most common causes.
- Q: Can I use a switching power supply?
Yes, most industrial controllers accept switching supplies. Ensure the supply has low ripple (<50mV) and can handle inrush current from relay outputs.
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Source: OEM Technical Manual
Category: PLC & VFD
Published: 2026-10-08
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