DELL n5010 runpwrok issue

[IamPritesh]

Hello friends and happy new year to all the lovely badcaps family.
Laptop N 5010 came with no display. Upon investigation found the PGOOD ( RUNPWROK) is missing . Now if I remove the +1.05V_VTT output COIL , the RUNPWROK is back at 3.3 volt.
Also +1.05V_VTT is not generated on TPS51218 (PU4901)

The readings on PU4901 is as follows with coil removed :

1 - 0V
2 - 0.8V
3 - 3.3V
4 - 0V
5 - 0V
6 - 0V
7 - 5V
8 - 0V
9 - 0V
10 - 5V
The impedance on the VTT coil is Good as well.
The mosfets on this DC DC converter is OK. What could be wrong ?

Thank you

[Sephir0th]

Re: DELL n5010 runpwrok issue

And resistance to GND measurements of the Pins with missing voltage (except GND)?

It seems the requirements are met. So, If +1.05_VTT looks healthy, it might be the time to inspect the buck converter more detailed. Start with the mosfets (are they internal shorted?) and replaced the Controller along with the mosfets if nothing turns out

[mcplslg123]

Re: DELL n5010 runpwrok issue

Replace PU5001 and very likely RUNPWROK will be back to 3.3V.Put PL4901 back.

[Th3_uN1Qu3]

Re: DELL n5010 runpwrok issue

Seconded (and thirded, it seems) the firm suggestion to replace PU5001 ALONG WITH BOTH MOSFETS AT THE SAME TIME. Put PL4901 back. Should run fine then.

Done this same mistake so many times for years and years and years myself, especially on VGA and battery charger circuits. Find mosfet short, replace mosfet, burns again on all terminals. Replace controller chip and burned mosfet, controller chip burns again. Replace controller chip a 3rd time. Mosfet burns.

Rinse and repeat and measure and check untill I FINALLY get fed up and "pull out the shotgun" - replace controller chip, ALL associated mosfets and low value gate resistors (if any) and all the fuses too. Then, the magic happens. The smoke stays in, the power supply delivers healthy voltage, the battery charges and the dedicated graphics card works unless it needs reballing.

There is an actual physical, electrical and very real and measurable explanation to this, it's not just "old technicians' talk", service bulletin or something you learn from experience. It's called MOSFET gate leakage. Look it up. You will find everything about it in less than 1 minute. Fully understanding what it means, why and how it happens and how you can prevent it from happening if you are the designer doing that power circuit could take many years, though.

[mcplslg123]

Re: DELL n5010 runpwrok issue

Agree with @Th3_uN1Qu3 to replace PWM along with high/low side fets. Thats the standard practice and we all do that. Since the OP is here for long time, i expect him to replace fets along with PWM though perhaps i should have mentioned it.