Certified IT Support Professional Learning Resources Troubleshoot SMPS

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Troubleshoot SMPS



 Take a small piece of wire and connect one end in GREEN wire port and other in the BLACK. Switch ON the supply if the fan in the smps is working the smps is good. If not open the cover and check whether the Capacitors inside the Smps is bulged on the top. If bulged replace the capacitor with the same value of the earlier.Check the voltages with a multimeter.


  •  Amphenol connector gives power supply to Mother Board
  •  Mole x gives power supply to IDE drives
  •  Mini Molex gives power supply to floppy drive.


 WIRE                                      VOLTAGE                              FUNCTION


Black                                                   0                                Ground

Blue                                                   -12                               Serial Data

Brown/Violet                                    +3.3                             Sensor

Gray                                                   +5                                Power good supply

Green                                                +5                                Power supply on/off

Orange                                              +3.3                             D Ram Refreshing

Purple                                                +5                                Stored by voltage

White                                                  -5                                 Refreshing Ram

Yellow                                                +12                              Motor Rotation

Red                                                     +5                                Logic circuit

General problems encountered are-

The computer boots normally, but behaves erratically after some time.


  • The power supply may not be able to support the load inside the computer.
  • The internal fan in the SMPS could have failed and excessive heat inside the SMPS might have caused the erratic output voltages.
  • Check whether the SMPS fan is functioning.
  • If the fan is okay, then switch off the power. Remove the power cable and open the cabinet..
  • Check the SMPS output voltages, after connecting the power cable and switching on the computer.
  • If the SMPS outputs are not satisfactory, then check by replacing the SMPS.
  • Now the problem is solved. Send the faulty SMPS for a service.

After adding one hard disk drive and one DVD drive to a computer, which already has a hard disk and CD writer, the computer does not start.


  • Remove all the power connectors, except connectors to the old drives and motherboard.
  • Connect each drive one by one and test.
  • After connecting all the drives, if the computer does not start, then it may be due to insufficient power from the SMPS. Replace the SMPS and check again.
  • If after connecting any particular device, then the problem may be due overload or faulty device.
  • Check on the SMPS, what is it’s output power rating.
  • For standard ATX computers, minimum 350 watts or 400 watts SMPS is sufficient.
  • Install a new SMPS with 400 watts power output and check
  • Now the computer works well. The problem is due to overload, because of adding more devices.

After switching on the computer, there was no display. Continuous beeps come, indicating some abnormal condition.


  • Check if power is available and the power cable is okay.
  • Check if the monitor is turned on, and the monitor LED is lit to green or blinking in orange-yellow.
  • Switch off power and disconnect the power cable.
  • Open the cabinet. Check whether all the cables are connected properly.
  • Check if all the memory modules are properly fixed to their slots
  • Insert a PCI VGA card, and connect to the monitor and switch on to check.
  • If the problem is not solved, check the SMPS output voltages.
  • Check with a new / working SMPS.
  • Continuous beeps may come due to problem in the SMPS.
  • Replace the SMPS and restore the system.
  • If the problem is not solved, then send the motherboard for a service /replacement.

After you assemble the new computer and switch on the power, it does not start.


  • Check whether the power is available at the power socket, using a multimeter or electrical tester.
  • Check whether the earth-line-neutral voltages are okay.
  • Open the cabinet and check whether all the front panel connectors are connected properly to the front panel header, on the motherboard
  • Check whether all the power connectors are properly fixed to the motherboard connectors. Check, whether the processor power connector is properly fixed.
  • Check if there is a switch at the back of SMPS, to switch the power on or off.
  • Keep the switch in ON state.
  • Check whether the system switches on. The system will now work.


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