HP 4540s no power

[buiduyhung9399]

I have an HP 4540s laptop that has been checked and confirmed to have no shorts or physical damage. However, I'm encountering an issue when connecting power. The LED indicator on the power jack briefly lights up and then immediately turns off. Upon powering, the current consumption is initially 0.022A and then slightly increases to 0.03A after about one second.

Using thermal camera, I observed that the 3V/5V IC begins to heat up mildly approximately one second after applying power. When measuring voltages, I found that the 3V and 5V briefly appear but then drop back to 0V after about one second. The 3V/5V (AUX) voltages, however, remain present.

Could anyone provide guidance on how to diagnose or resolve this issue? Any help or suggestions would be greatly appreciated. Thank you very much.

[buiduyhung9399]

Help!

[mcplslg123]

The dc jack light behaviour is perfetly normal for a probook.

The 3V/5V regulator is also behaving correctly as DSW is activated.

In summary, nothing wrong so far. Move ahead and check the mb for corrossion/liquid spill.

If nothing visible, check RSMRST#/ECRST# present or not?

have u checked RTC section?

[skydec]

Hi,
I also just got one HP 4540s with similar problem. After plugging in the power adapter power led blinks few times and the fan spins for a second and after that full shutdown fan stops and all lights go dark. I don't have the battery to test it.
Pressing the power button turns the fan on and few blinks from power led and after a second full shut down by itself.
After disassembly mainboard behaves the same with no cpu, ram, wlan or anything connected to it except power adapter, tried with more adapters, same story, they all work on other laptops.
Power button works fine, 3.3V power on is there, goes down on power button press and goes up to 3.3V release of button.
I tested the 19V main rail and it is in the laptop, 5V and 3V on PL4101 and PL4102 are ok, no inductors is in short circuit with ground (vga is low like 10ohm, and if cpu is in socket then cpu are also low but I think it is normal)
I started pulling inductors out of mbo and after pulling the PL4801 VCCSA the laptop stopped to shutdown after a second, now it the fan runs for 3 seconds and the power light is on, then for a bit like it restarts, and again fans spins for 3 seconds.
Got the schematic from https://www.badcaps.net/forum/troubl...ately-turn-off
On page 48 - TPS51461 for VCCSA in the table it shows that the VCCSA should be between 0.675 and 0.9V, my chip shows 0.4V on SW pins and after a few restarts nothing 0V, VIN pin is 5V always, EN is 3.3V when the fan is spinning, goes down on restarts
Now since I'm not experienced with the chip level repair what could be the problem?
I could try to reflow the GPU but I do not think it is the problem. Should I just order new TPS51461 and replace it or is the chip detecting some problem or getting wrong signals so its not generating output power?
How can I know what voltage should be on each pin and how to know if the problem is the chip of something else?
https://www.ti.com/lit/ds/symlink/tps51461.pdf
pin v TPS51461
1GND
2 VREF 2V
3 COMP 2.5V
4 SLEW 0.9V
5 VOUT 0V
6 MODE 0V

8,9,10,11 SW - at first 0.4V then 0V
12 BST 4.8V

13 EN 3.4V
14 VID0 0V
15 VID1 0V
16 PGOOD 0V
17 V5FILT 5.1V
18 V5DRV 5.1V

19,20,21 PGND 0V
22,23,24 VIN 5.1V

[mon2]

What is the history of the unit? If known. Using the official power adapter?

Suggest to remove all power. Meter in resistance mode. Measure the resistance to ground of each and every inductor on the board. Testing for a low resistance which may indicate a shorted part on the board and causing an excessive current draw so the local power rail is shutting down. Post any suspects.

Any power rail output that is not within spec is a suspect. Measure the resistance (without power to the board) of such rails. Respectively, if the ENABLE pin is a logic '1' then this implies the upstream logic is requesting to power on that power rail and this is a good sign. The GPU is of concern when the GPU is active under graphics intensive s/w. Often, the GPU is a no care during initial power up.