ASUS TP412F 3.3V Regulator chip gets very hot

[mferna14]

Hi all., I am working an ASUS TP412F., motherboard Model TP412FAC R: 2.0. The problem I am facing is the 3.3 buck converter (L8=7J RT6256BGQUF) gets very hot when 19v is applied through DC-in jack. I don't think Schematics or Boardview is availble for this model. The chip get so hot that I can't even take the voltages of the pins. I replaced the chip but the problem is still there, new chip even gets very hot. The input on pin 5, 19v is present. So I removed the Output coil & the chip & checked the voltages on the chip pads which are as below: Please view if any volts seem to be abnormal.

Pin 1: 0v
Pin 2 & 3: 0v
Pin 4 : GND
Pin 5: 19v
Pin 6: 0.045V
Pin 7: 0.097V
Pin 8 & 9 : 0 v
Pin 10: 0.42V
Pin 11: 0.1V
Pin 12: 0V

Any tips or help will be greatly appreciated., Thanks

[mon2]

For each output, measure the resistance to ground. Someone is shorting and causing an excessive load, leading to heat. If the loads are removed or disabled, this regulator should be cool.

[mcplslg123]

3.3V LDO resistance to GND?

[mferna14]

Dear friends., I got the ohms readings. I soldered back the RT6256BGQUF & the inductor. Only removed the IO chip. Turned it on without the IO chip but still this chip RT6256BGQUF gets hot. Anyway the readings are as below:

BOOT (Pin 1) 1.3M
LX (Pin 2 & Pin 3 OUTPUT 3.3V) 3.6K
PGND (Pin 4) 0 Ohms
VIN (Pin 5) 17K
EN (Pin 6) 49K
PGOOD (Pin 7) 159K
AGDD (Pin 8) 0 ohms
VCC (Pin 9) 367K
VOUT (Pin 10) 3.6K
LDO3 (Pin 11) 13.5K
FF (Pin 12) 19.4K

Thank you for the help

[jasko_jacker]

Have you a boardview ? without the boardview it is very difficult to look for a solution

[mferna14]

No Boardview or Schematics available... I searched & ask for it, not available.

[mon2]

Can you confirm that this regulator is the original for this PCB location?

Can you test with a fresh part here? You still have time to order this for a potential delivery for tomorrow from DK:

RT6256BGQUF Richtek USA Inc. | Integrated Circuits (ICs) | DigiKey

NB: Our order that arrived today took 2 days from DK due to some delay with Fedex.

[mferna14]

Thanks mon2., I have a dicto similar board TP412C, only difference, components seems to be the same, layout a bit different. I removed RT6256BGQUF from a good working board. So I can eliminate this. This is why I came to know that this IC works on good board. I need to have the schematics or boardview for further trouble shooting.

[mcplslg123]

No shorts on any of the pins of this IC. Really cant see any reason for its hotting up except short in RTC.
Remember 3.3V LDO goes to RTC as well. So only probable reason is short in RTC section.
You have sufficient experience to trace RTc circuit without schematic. So go ahead and probe RTC section.

[mferna14]

Yes @mcplslg123., surely will trouble shot the RTC Section & will come up with an answer. thanks friends