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I have opened up my friend's laptop and cleaned up the fan and changed the thermal paste. Then, I closed it up and the screen did not work. Also, connecting a monitor via VGA doesn't help, the monitor does not show anything.

On the motherboard, near the screen connector, there is an IC with designator U1, and I am guessing it is an LDO. It is marked 1Y=61J.

Two pins, 4 and 5, are shorted together and I measure 3.4 V on them. On the other pins, I measure nothing, and they are not shorted to ground except for one pin, pin 2, which is obviously the ground pin. Pin 3 goes to a capacitor and to the screen connector. I've checked the fuse and it is shorted.

Here are some close up photos, click on them for high-resolution: enter image description here

enter image description here

Edit:

The problem was with the male connector. I have accidentally damaged some pins while connecting it. Problem is solved now. Also, it seems like this is not an LDO, instead it has some kind of transistors that pull some pins to GND.

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  • \$\begingroup\$ 61J is usually a MMBF4091, except it doesn't have enough pins... \$\endgroup\$ – Ignacio Vazquez-Abrams Sep 2 '13 at 12:18
  • \$\begingroup\$ It may be a proprietary part. \$\endgroup\$ – tcrosley Sep 27 '13 at 0:18
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Richtek RT9724

100mΩ, 2A Slew Rate Controlled Load Switch

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  • \$\begingroup\$ Good find. 10 points to Gryffindor. \$\endgroup\$ – Ignacio Vazquez-Abrams Oct 9 '13 at 17:16
  • \$\begingroup\$ Great find! How did you do this? \$\endgroup\$ – abdullah kahraman Oct 10 '13 at 7:30
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    \$\begingroup\$ Google for sot-23-5 "1y=" \$\endgroup\$ – realtime Oct 10 '13 at 9:21
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I know you figured it out but I'll provide some insight as to what to think when seeing these:

An LDO is only sometimes in a SOT23-5 package. They will usually be in a different package that allows for much better heat dissipation. Its usually that SOT23-5 and SOT23-6 are related to driving logic.

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