Brittle mb 15256-3 no power

[ahmarzo]

I have brittle mb 15256-3 with no power and no led on dc jack. Ic pu4501 get heated it number is 5x=4e.it is 6575d please help me how to solve this problem.
I have vin 19 v, 5v ldo is present and 3v ldo gets drop to 2v.
How to solve this problem.

[mon2]

Re: Brittle mb 15256-3 no power

Hi.

1) Post or link the schematic if on this forum.

2) Is the Richtek regulator very hot ? It may be defective. You can remove all power -> check the resistance to ground on the output pins to see if there is a shorted cap.

3) Remove all power -> check the usual DCin mosfets that are linked to the charger IC. Which charger IC is onboard this logic board ?

A good idea to measure and post the voltages present on the charger IC.

Often the trouble is with the first 2 DCin mosfets.

[mcplslg123]

Re: Brittle mb 15256-3 no power

3V ldo is dropping to 2V- There can be two reasons.
01. The regulator it self is bad,corroded or nearby components are bad.
02.There is some short on 3V LDO line.

What is the exact resistance on 3V LDO pin(Meter set to 200K sacle or higher), No power attached.

[ahmarzo]

Re: Brittle mb 15256-3 no power

Thanks for reply. 3v ldo line resistance is 256 ohms Without connecting power. There is no shorting capacitor nearby i have arranged the ic and will reply after changing it. Thanks again

[mcplslg123]

Re: Brittle mb 15256-3 no power

Resistance on 3V LDO is 256 Ohms and thats too low. Dont replace the ic yet. Remove the IC from board and re-measure resistance on 3V LDO pin?? Is it still same or has gone higher in Kohms??
PSont connect power to mb while 3/5V regulator is off the board.