Chip Level Repairing SMPS NOTES



A/C 220V/230V  supply is given to the line filter section.

A line filter coil is connected in this section which function to remove any noise that may come with the input AC supply. The filtered AC supply is received from the line filter section is given to the Bridge rectifier section converts the AC supply into High voltage DC supply. High voltage DC supply received from bridge rectifier section is given to the filter section when removes any ripples from the rectifier DC supply and forms a smooth

DC supply. Two filter capacitors are connected in the filter section which function to filter the DC supply in this manner ,an unregulated high   supply is received from the output of filter section.


In a common types of SMPS this unregulated high voltage dc supply is converted into high frequency current pulses by switching transistor. When this high frequency current pulses pass through the primary winding of a transformer.  AC

Volts get induced in the secondary winding .But instead of using this technical in a computer SMPS an  SM transformer is used. High frequency signal is given to its primary winding to get the necessary supplies from its secondary winding. This high frequency signal is generated by an oscillator section and this signal is amplified by driver section.  amplified signal received from the driver section is given to the power output section through the driver transformer. The driver transformer functions as a coupling between the power output and power driver section. Amplified signal received from the power output section is given to the primary winding of the SM transformer through the secondary winding of protector transformer. AC volts are induced in the secondary winding of the SM transformer because of this high frequency pulses. The induced AC volts are rectified and regulated to get the necessary supplies that are used for the different section of the computer.


As the high frequency signal which reaches the primary winding of the SM transformer passes through the primary winding of the protector transformer, volts get induced in it’s secondary winding also, whenever these some fault in the output supply such as a short circuit or if there is overloading of the power supply then the volts induced in the secondary winding of the protector transformer also register a change these volts induced in the secondary winding of the protector transformer are rectified and filtered before these are given to the protector section. Protector section sense the variation in these volts and cut off the output supplies whenever there is some fault in the output supply.


Power supplies are two types

  1. AT power supply.
  2. ATX power supply.

1.AT  power supply





  1. Power good signal.
  2. +5v
  3. +12v
  4. -12v
  5. GND
  6. GND
  7. GND
  8. GND
  9. -5V
  10. +5V
  11. +5V
  12. +5V.


2.ATX Power supply





  1. Rectifier and filter section
  2. Output switching section
  3. Oscillator driver and Error amplifier section
  4. Protector section
  5. Output  supply voltage section
  6. Power good section.



  1. For P.C 65 Wattage
  2. For P.C/XT 120 WATTAGE
  3. For P.C/AT 286 150 WATTAGE
  4. For P.C/ super AT386 200 WATTAGE
  5. For P.C/486 250 WATTAGE
  6. For P.C/P1,P2,P3 300 WATTAGE
  7. For P4 450 WATTAGE.




  1. If any components are open,output supply will be high.
  2. If any capacitors are short output supply will be low.
  3. If any main capacitors discharging for using 47 ohms 5 watt wire wound resistor.


  1. check the power cable
  2. check the on/off switch
  3. check the bridge rectifier
  4. check the capacitors
  5. check the output switching transistor
  6. check the output rectifier and capacitors of SM transformer secondary side.

2.Low output supply coming from SMPS:

  1. check the main capacitor voltage 330v
  2. check the oscillator I.C and related components
  3. check the secondary side SM transformer filter capacitor,diodes.
  4. check the driver transistor

3.SMPS working but no output:

  1. check the power good section
  2. if any components is defective. If  defective replace it.
  3. check the protector transistor or IC
  4. check the output capacitors and diodes.

4.AC fuse blow off:

  1. check the bridge rectifier
  2. check the main filter capacitor
  3. check the switching transistor
  4. check the related components of bridge rectifier and switching transistor.

5.System automatically restarted:

  1. check the input capacitors and check the output capacitors
  2. check the all capacitors which are surrounding of SMPS transformer.
  3. check the oscillator and the error amplifier I.C or related components.

6.System late starting:

  1. check the input capacitors and replace it.
  2. check the output capacitors.









The block diagram can be divided in two major areas.The control section and the driver section. The control section is dedicated to the peripheral interface it connects to the PC ‘s driver controller.


The driver section electronics will manage all the CD-ROM’S physical operations As well as EMF decoding and error corruction. Driver circuitary converts and analog output from the layor diode. into an EMF signal, which is interm decoded into binary data and CIRC(cross interleaved read Solomon code) information.


A drive controller chip and servo processor chip are responsible for directing laser focus, tracking sled motor control, spindle motor control and loading unloading motor control.


CD(compact disk):

The compact disk first appear in the commercial market place in the year 1982 introduced by Sony & Philips.


Mechanical Assembly spare parts:

  1. Lense—it is using for Read/Write the data.
  2. Spindle motor—it is using for spin the CD/DVD
  3. Belt—it is using for locking the tray &CD/DVD locking
  4. Gear wheel set— it is using for locking the tray &CD/DVD locking.
  5. Tray motor—it is using for moving the tray from open to close,close to open
  6. Slid motor—it is using for lence slide the top to bottom,bottom to top.
  7. Data cables—it is using for data signals carring the MLC to lence or MLC to front panel.


CD Data transfer speed:

  1. The data transfer speed is 150kilo bytes/sec

Ex:      2x   =300kb/sec

4x   =600kb/sec

50x   =7.5 mb/sec.

Note:     AT 50X CD  with 650 MB of data can ideally by read in 86.7 seconds.

2.CD-ROM spindle motor speed is 200 and 500 rpm.


DVD Data transfer speed:

1.DVD data transfer speed is 2.7MB/sec

Ex:  12x   = 16.2 mb/sec speed

16x    =22.1 mb/sec speed

Note:            The drive also lists an interface rate of 33.3mb/sec by using ultra DM model 11 and 16.6mb/sec at multimode model-11.

2.DVD access time is 120 micro seconds to 200 microseconds.


Carraying for CD’s:


1.Don’t bend the disk

  1. Don’t heat the disk
  2. Don’t scratch the disk
  3. Don’t use chemical on the disk



Trouble Shooting:

  1. check the belt
  2. check the gear wheel set and liver
  3. check the data cables MLC to lence,MLC to spindle
  4. check the spindle motor
  5. check the lence
  6. servo processor

Tray problem:

  1. check the belt
  2. check the gear wheel set and liver
  3. check the data cable from MLC to front panel
  4. check tray motor
  5. check the servo processor I.C

Reading problem:

  1. check the data cable from MLC to lence.
  2. check the lence motor and gear wheel
  3. check the lence shaft
  4. check the disk motor
  5. check the lence and replace the lence
  6. check the Buffer IC to lence

CD ROM/CD WRITER/DVD ROM/WRITER not working(dead condition):

  • check the power connector
  • Dry solder the power connector
  • Check the voltages 5v,12v supply to MLC.

Note:   5v  using for buffer IC and 12v using for servo processor IC to disk motor,motor and front panel.

  • Check the servo processor IC.

5.Drive not detected:

  • Check the IDE cable
  • Check the BIOS setup
  • Check the interface to buffer IC.