Probook 640 G1 turns on when adapter connected

[loopster]

Hi all, got the following issue. As soon as I plug in the AC power adapter or the battery, the laptop comes to life and the fan is spinning full speed. Wifi and audio mute button are lit, however the laptop is still off.
When I press the power on button, the laptop runs normally until I put it to sleep or shut it down. Then I am back to the fan running at full speed and a lit Wifi and audio mute button.

I've looked around, and it is basically the same problem as in this thread:
https://www.badcaps.net/forum/showthread.php?t=93574

I am wondering whether TPS51225CRUKR (U6100) is causing the problem in my case.

Could someone have a quick look at the schematics and give me a clue, please?

[mcplslg123]

Re: Probook 640 G1 turns on when adapter connected

Check Pg19.Pin3 voltage of Q7050/7100?? fan etc are running even in off condition 'coz your dc-dc transfer is happening without turning on. So something wrong in Pg19 circuit.

[loopster]

Re: Probook 640 G1 turns on when adapter connected

Thanks mcplslg123 for giving your input, I really appreciate it.

Q7050 and Q7100 both have 9V on Gate and 3.3V, respectively 5.0V on Source and Drain. Since Q7050 and Q7100 (AO6402AL) are n-channel mosfets, they function correctly, by which I mean, as they are instructed, don't they?

However, I really don't understand the functionality of the whole circuit.

Q7101 (SSM3K7002BFU) has 0.3V on Gate, 0V on Source and 5.0V on Drain.
Anything else I should check?

[mcplslg123]

Re: Probook 640 G1 turns on when adapter connected

Are these measurements in power off condition or power on condition?? All the measurements are good in power on condition but if these are the measurements in power off condition ,then they are wrong.

[loopster]

Re: Probook 640 G1 turns on when adapter connected

The measurements were all made in power off condition, with fan full speed
and wifi and mute button lit.

[loopster]

Re: Probook 640 G1 turns on when adapter connected

According to this thread: https://www.badcaps.net/forum/showthread.php?t=107505
the problem is the dc-dc converter for 3V/5V also in my case;
which would be TPS51225CRUKR (U6100).
Should I change it, or could something else be the problem?
Where can i check?

[mcplslg123]

Re: Probook 640 G1 turns on when adapter connected

TPS51225 is your 3V/5V PWM IC. Q7055 gate should be High so that ground(pin2) travels to source(pin3) as its a n channel mosfet. Once the ground reaches pin3, it will block P15VOA line and voltage wont be transferred on Pin4 of Q7050. This should be the boards behaviour in off condition.SLP_S3_5R status in off condition?

[loopster]

Re: Probook 640 G1 turns on when adapter connected

Once the ground reaches pin3, it will block P15VOA line and voltage wont be transferred on Pin4 of Q7050. This should be the boards behaviour in off condition.SLP_S3_5R status in off condition?

Did you mean to write "voltage wont be transferred on Pin3 of Q7050",
because that's where Pin 3 of Q7055 is connecting with Q7050?

Anyway,

Q7055 (SSM3K7002BFU) in off condition (fan full speed).
Pin 1 (G): Fluctuating 0.0 - 0.8V
Pin 2 (S): 0.0V
Pin 3 (D): 9.0V

SLP_S3_5R measures 0.26V on Pin 1 (SLP_S3_5R) - Gate of Q1306
in off condition. I can't measure SLP_S3_5R on Pin 1 of Q4501,
because I can't locate the damn component on the board.

[mcplslg123]

Re: Probook 640 G1 turns on when adapter connected

What i wrote about voltage transfer on Q7050 is absolutely correct. You seems not to understand it. SLP_S3_5R must be 3V in off condition and it should pull low only when turned on. So you need to findout why this is so.

[loopster]

Re: Probook 640 G1 turns on when adapter connected

"SLP_S3_5R must be 3V" Oh yeah sry, now I got it :-)
Thanks for your assistance.

[loopster]

Re: Probook 640 G1 turns on when adapter connected

Finally got round to have access to a proper scope and upon closer inspection, I found that
Q4751, which is some sort of temperature signal mosfet, has got visible corrossion on all of its legs. The 640 G1 has no dedicated GPU, nevertheless, could this chip be the reason why the fan goes haywire as soon as the laptop gets voltage, but works normally when powered on?

[mon2]

Re: Probook 640 G1 turns on when adapter connected

Yes. The dual mosfets are acting like bus switches for the smbus lines which are feeding to the PCH.

In the absence of the thermal data, the fans can go into hyper mode.

Best to flux this part and reflow it with high heat but low air pressure so the small parts do not go flying.

Good catch to find this fault!

[loopster]

Re: Probook 640 G1 turns on when adapter connected

Thanks for your confirmation, I haven't done any microsoldering under a scope or with a hot air station yet myself, and won't start with it until I have my own equipment or can practice properly before I let myself loose on salvagable stuff.
I'll hand this over to a buddy of mine, I am sure he will get the job done easily.
Thanks for your help.

[loopster]

Re: Probook 640 G1 turns on when adapter connected

Just to close this thread. The original dual mosfet was defective.
Replacing Q4751 fixed the issue. Laptop works normal again.