fujitsu t730 mb power draw from ac adapter

[nule4]

hi, im newbee to all of this, but learning. i have problem to locate failed component on motherboard. laptop suddenly stop working, no signs of life at all. try measuring power rails, but as soon i connected before measured multiple power adapters (all of them gave me 19V and working on another laptops), and start measuring first spot on mb (black on ground and red on red wire on mb power connector) it showing power fluctuacting from 0.40V to 0.60V instead 19V. from one ac adapter heard clicking sound, from another ac adapter standby led start blinking. any help would be greatly appreciated. thanks.

[mon2]

Disconnect the power adapter. Meter in DC voltage mode (30v or higher scale is ok). Connect your meter to the center tip / ring of the power adapter (RED probe); outside ring (ground = BLACK probe). You should be able to measure ~19v if the power adapter is still ok.

Next, remove all power from the mother board. Meter in resistance mode. Connect one probe (either colour since resistance does not care about the polarity) to the main power rail connector pin; other probe to ground (any metallic shield is ok). What is the exact resistance?

If you are tanking the power adapter voltage from 19v to almost zero, then you have a shorted part on the board. Could be a bad capacitor but first confirm the same with the resistance check. Post the measurements. Again, no power to the board during resistance checks.

[nule4]

thanks. resistence is between 54-60 ohms, black on ground red on main power rail, vise versa show nothing.

[mon2]

Locate the DCin power connector on the board. Measure the same resistance to ground. Is the resistance this low at the DCin connector? If yes, then the circuit from the DCin connector to the first mosfet are suspects.

[nule4]

it is little higher.

[mon2]

Next, you must locate the first DCin mosfet in the path from this same DCin connector on the motherboard. All parts from this DCin connector to the first mosfet are suspects due to the low resistance. Suggest to flux and remove the first DCin mosfet and test if the resistance is still this low or not. If yes, the remaining parts in this power path are suspects. Someone is shorted in this region.

Take pics of your motherboard and also the DCin mosfets for proper resoldering of each. Some of the parts like the mosfets are with a polarity. Ceramic caps and resistors do not matter on their orientation on the PCB.

[nule4]

thank you, i will try that.

[mon2]

The issue will most likely be a bad / shorted cap but it is ok to remove the DCin mosfet to isolate the circuits. Do so only if you feel comfortable with the hot air tools.