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How to repair LCD monitor Samsung SyncMaster 920NW

How to repair LCD monitor Samsung SyncMaster 920NW
How to repair LCD monitor Samsung SyncMaster 920NW
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In this article we'll give a real life example on how the monitor's internal power supply was repaired.

Very often, after 3-4 years of service LCD monitors SyncMaster simply cease to be work (even the LED on the power button doesn't light up). The reason is poor quality components in the internal power supply. The good news is it's fixable! Well, let's investigate.

First unscrew the stand:

First unscrew stand

Gently, using a guitar pick release all the clips of the case:

Release all clips of case

Remove the back cover:

Remove back cover

Unplug the connector leading to the matrix:

Unplug connector leading to matrix

And now lamp connector (hidden under protective cover and held with a clip):

Lamp connector

Remove the piece of metal to which the boards are bolted to and you'll see a clear imprint of something burnt on the matrix:

Remove piece of metal

After careful inspection of the board we see a cinder burnt PWM chip controller NCP1337:

Cinder burnt PWM chip controller NCP1337

Unscrew the board of the power supply inverter and conduct a detailed inspection. We can see that NCP1337 is not the only thing that burned out. It's clearly visible that some traces of burnt residue come from resistor R805 (0.24 Ohm, 2W). Also resistor R806 (10 Ohm, 0.125W) is visually defined as "gone beyond repair". In addition, the capacitors C818 1000mFx10V and C815 1000mFx25V are swollen:

Board of power supply inverter

Final list of burned parts after a long test night:

  • Transistor Q804 AP2761
  • Microchip IC802 NCP1337
  • Resistor R812 10 kOhms SMD (when soldered out shows 38 kOhms)
  • Resistor R832 1,2 kOhms SMD (disconnected)
  • Resistor R807 1,2 kOhms SMD (shows up to 2.1 kOhms)
  • Resistor R806 10 Ohms 0,125 W (shows up to 34 kOhms, probably it's burnt)
  • Resistor R805 0,24 Ohms 2 W (disconnected, didn't find similar in a shop, had to put two resistors with value 0.47 in parallel)
  • Capacitor C818 1000x10V (swollen)
  • Capacitor C815 1000x25V (swollen)
  • Capacitor C501 470x25V (just to be on the safe side I replaced it)
  • Capacitor C817 470x25V (just in case, replaced to prevent further complications)
  • Fuse F801 2A.
Burned parts

Yep, general conclusion - the monitor was utterly fried;). What was the reason? I see it this way, the main reason was swollen capacitors, and as a consequence increased current overloaded the transistor Q804. The rest was merely the consequence of the transistor's failure.

Well, reassemble in reversed order and turn the monitor on.



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