Lenovo Yoga 2 LA-A921P No DDR Voltage

[KvnTM]

Hi!

I need some help/advice with an Lenovo LA-A921P Board.
It turns on but the RAM Voltage is missing. The previous owner shorted B+ to GND on PL501. The RAM Shield touched the inductor.

Every Power rail is OK except for RAM.
+1.35VP is 0.2V

Is it either the controller PU501 (RT8207) or one of the Mosfets?
PQ501 (AON7408L) & PQ502 (AON7506)
They don't seem to be shorted. Drain to Source is a few MOhm's.

I attached the Schematic.
Thanks!

[caspian]

Re: Lenovo Yoga 2 LA-A921P No DDR Voltage

what is +1.35VP with another RAM or without any RAM?

[Techtiger]

Re: Lenovo Yoga 2 LA-A921P No DDR Voltage

The 2 Fets Voltage are contrôle by RT8207, pin 5 of PQ501 need B+ test the Voltage , remove one pad of PL502 test the resestence to GND both sides, and check if RT8207 getting Voltage on pin 11 5 7 8 9 4 20

[KvnTM]

Re: Lenovo Yoga 2 LA-A921P No DDR Voltage

what is +1.35VP with another RAM or without any RAM?

RAM is soldered to the Mainboard.
Resistance from +1.35VP to GND is around 108Ohms. Should be OK

+5VALW is present so the chip is getting power.
CPU gets warm and keyboard backlight turns on. Also it beeps when connecting/disconnecting the charger.
So I guess it POST's but can't access the RAM obviously.

SYSON is 3.3V
TON was around 0.9V iirc.

[KvnTM]

Re: Lenovo Yoga 2 LA-A921P No DDR Voltage

The 2 Fets Voltage are contrôle by RT8207

Yeah I know but i'm not sure if the controller is dead or the fets.

[KvnTM]

Re: Lenovo Yoga 2 LA-A921P No DDR Voltage

I've made measurements

RT8207
Pin 1: 0V
Pin 2: 0.02V
Pin 3: GND
Pin 4: 0.02V
Pin 5: 0.03V
Pin 6: 0.01V - 0.02V
Pin 7: 4.9V
Pin 8: 3.25V
Pin 9: 0.56V
Pin 10: NC
Pin 11: 5V
Pin 12: 5V
Pin 13: 4.43V
Pin 14: GND
Pin 15: 0V
Pin 16: 0.03V
Pin 17: 0.03V
Pin 18: 5.3V
Pin 19: 0.03V
Pin 20: 0.02V

[Techtiger]

Re: Lenovo Yoga 2 LA-A921P No DDR Voltage

I've made measurements

RT8207
Pin 1: 0V
Pin 2: 0.02V
Pin 3: GND
Pin 4: 0.02V
Pin 5: 0.03V
Pin 6: 0.01V - 0.02V
Pin 7: 4.9V
Pin 8: 3.25V
Pin 9: 0.56V
Pin 10: NC
Pin 11: 5V
Pin 12: 5V
Pin 13: 4.43V
Pin 14: GND
Pin 15: 0V
Pin 16: 0.03V
Pin 17: 0.03V
Pin 18: 5.3V
Pin 19: 0.03V
Pin 20: 0.02V

Voltage in pin 7 S3 should be around +3V it's to high track it Back

[KvnTM]

Re: Lenovo Yoga 2 LA-A921P No DDR Voltage

Well, good news. I fixed it!

The pcb track under PL501 was soooo thin and burned away that i could measure proper voltages but it couldn't handle enough to current and the RT8207 wasn't starting properly.

Removed that stupid "EMI" inductor, reworked the pub & bridged the pads and et voila. It works.

Thanks for your responses though!