Lenovo ThinkPad 11e (DALI6JMB8E1 REV:E) not powering On

[classicandy]

Hi, I have a Lenovo ThinkPad 11e (DALI6JMB8E1 REV:E) that is not powering On.

Immediately i plug the charger, the 3.3v/5v I.C gets extremely hot. I don't have the schematic yet.

[piernov]

Re: Lenovo ThinkPad 11e (DALI6JMB8E1 REV:E) not powering On

Check for short to ground on outputs of 3V/5V regulator. (LDOs and buck converters)

[classicandy]

Re: Lenovo ThinkPad 11e (DALI6JMB8E1 REV:E) not powering On

Before that I.C started getting hot, there was a buzzing sound coming from a component close to the DCIN Jack. Check the photo attached. I think the charger was faulty too which caused it to make that sound.

I have replaced the charging I.C (BQ715), it still made that noise until the noise stopped and the 3.3v/5v I.C started getting HOT. I've changed the Charger and also the 3.3v/5v I.C, it still gets hot.

[classicandy]

Re: Lenovo ThinkPad 11e (DALI6JMB8E1 REV:E) not powering On

Check for short to ground on outputs of 3V/5V regulator. (LDOs and buck converters)

Ok.

The previous 3.3v/5v I.C was TPS51285B and i replaced it with TPS51225. Both still gets hot.

From the datasheets, they are very similar. Should i be worried or its still compatible?

Thanks for the quick reply

[piernov]

Re: Lenovo ThinkPad 11e (DALI6JMB8E1 REV:E) not powering On

TPS51285B and TPS51225 are not directly compatible (VREG5 is off by default for TPS51225 and on by default for TPS51285B, switching frequencies are different so it may require different values for output filters). That's not the problem here though.

[classicandy]

Re: Lenovo ThinkPad 11e (DALI6JMB8E1 REV:E) not powering On

Check for short to ground on outputs of 3V/5V regulator. (LDOs and buck converters)

No short to ground on VREG3 (pin 3) and VREG5 (pin 13).
186k ohms on both outputs.

VCLK (PIN 19) = 78K ohms
SW1 (PIN 18) = 114K
SW2 (PIN 8) = 126K
PGOOD (PIN 7) = 14.4K
DRVL2 (PIN 11) = 95K
DRVL1 (PIN 15) = 96K
DRVH2 (PIN 10) = 125K
DRVH1 (PIN 16) = 118K
CS2 (PIN 5) = 11.3K
CS1 (PIN 1) = 11.3K


Also, i've removed inductors for 3.3v and 5v outputs, so no connection on that rail to the rest of the board.

[classicandy]

Re: Lenovo ThinkPad 11e (DALI6JMB8E1 REV:E) not powering On

TPS51285B and TPS51225 are not directly compatible (VREG5 is off by default for TPS51225 and on by default for TPS51285B, switching frequencies are different so it may require different values for output filters). That's not the problem here though.

Ok, I can change it back. Seems the previous one (TPS51285B) might still be good.

[piernov]

Re: Lenovo ThinkPad 11e (DALI6JMB8E1 REV:E) not powering On

Weird, check if the MOSFETs for the buck converters are shorted drain/source/gate. (it may be normal to have low resistance between gate and source with the regulator soldered to the board, but it should not be 0 ohm)

[classicandy]

Re: Lenovo ThinkPad 11e (DALI6JMB8E1 REV:E) not powering On

Weird, check if the MOSFETs for the buck converters are shorted drain/source/gate. (it may be normal to have low resistance between gate and source with the regulator soldered to the board, but it should not be 0 ohm)

ok.

no shorts on the MOSFETs

[mcplslg123]

Re: Lenovo ThinkPad 11e (DALI6JMB8E1 REV:E) not powering On

check kbc for shorting.

[classicandy]

Re: Lenovo ThinkPad 11e (DALI6JMB8E1 REV:E) not powering On

check kbc for shorting.

Thanks for the suggestion, I found KBC to be shortened. After removing KBC, short was gone. Sorry for not replying on time.