Dell Latitude 3390 2 in 1 - nie wlącza się

Witam,

DELL Latitude 3390
Płyta: 17810-1
CN-0K3GFH

Laptop pobiera, 0.02A po podłączeniu zasilacza i kompletnie nie reaguje na przycisk włączenia.
Rezystancje na cewkach są prawidłowe. Jedynym elementem który się w owym czasie delikatnie grzeje to KBC.

Na początku oczywiście próbowałem zmienić BIOS - brak poprawy
Zmiana KBC - brak poprawy
Wrócenie do oryginalnego wsadu BIOS - brak poprawy.

W pewnym momencie, kiedy załączyłem zasilanie laptop się uruchomił bez problemów ale po wyłączeniu zasilania, problem znów wrócił.

Podczas poboru prądu 0.02A, napięcie na cewkach:

PL4501 - 3,4V
PL4502- 5,2V
PL4401- 0,16V

Na kości bios 3,3V.
Na przycisku power 3,3V i spada do 0V po naciśnięciu ale prad stoi w miejscu.

Reszta cewek nie ma żadnych napięć.
Sytuacja poprawnego włączenia się płyty powtórzyła się 7 razy i tylko wtedy kiedy płyta byłą ciepła.

Proszę o pomoc.

Measure the voltages on pins 2, 10, 11, 13, 16, 17 of PU5101.
Measure the voltages on pins 1, 3, 6, 7, 9, 10 of PU5102.

Hello,

PU5101:
2 - 20V
10 - 0V
11 - 0,01V
13 - 0,0133V
16 - 0V
17 - 0V

PU5102:
1 - 0V
3 - 0V
6 - 0V
7 - 0V
9 - 0,0133V
10 - 5,21V

Measure the voltages on pins 4, 18, 27, 30, 36, 43, 48, 88, 111, 121, 122, 128 of KBC.
Measure the voltages on pins 52, 127 of the KBC in the following cases:
at power off
with power on pressed
at power on.

4 - 1,27V !
18 - 1,17V
27 - 0V
30 - 0V
36 -3,43V
43 - 3,34V
48 - 0V
88 - 3,41V
111 - 2,27V
121 -3,14 V
122 - 3,12 V
128 . 3,46 V

52:
at power off - 1,34 V !
with power on pressed - 1,34 V !
at power on - 1,34 V !

127:
at power off - 3,14 V
with power on pressed - 0V
at power on - 3,14V

When I touch the plate during the measurements marked with an exclamation point, the reading changes significantly—as if there were a difference in potential or an issue with the grounding.

Measure the voltages on pins 9, 17 of PU4501.
Measure the resistance to ground on pin 52 of KBC.

PU4501:
9 - 3,4 V
17 - 3,4 V

KBC - n. 52 to GND ~ 2,1 Mohm

Measure the voltages on pins 4 of U4006.
Is the voltage measured on pin 27 of the KBC correct?
Measure the voltages on all pins of Q1701.

U4006:
n.4 = 0.0098V

Q1701:
n.2 (3V_5V_POK_C) = 3,43 V
n.3 (PM_RSMRST#) = 0V
n.5 (3V_5V_POK#) = 0V
n.6 (3V_5V_POK#) = 0V

Yes, I'm sure. I checked three times on pin 27 of the KBC as well as on resistor R1702, and the result is still 0.0020V.

Measure the resistance to ground on pin 3 of Q1701 if it is low replace Q1701.

pin 3 has a resistance of 10kohm.. but when I heat the IC area ((trying to heat the chip itself) with hot air, the laptop starts every time.

Could you tell me what this IC is?? I don't have a description on boardview, only a marking on the laminate.

I found the same chip marked 8KD on a Lenovo board.

After the replacement, the motherboard started up every time (around 30 times), but without displaying any image.
The current stopped at 140mA one second after startup.
At the start, the current was around 180mA. There was no image on the screen.
I tried using different RAM modules. After 30 attempts, the problem returned.

I noticed that if I press the board at the marked spot with my fingers, the motherboard starts up with the effect described above.

and.. The fan is running at maximum speed.

Check the soldering in the area where you press.
Check, by pressing the power button several times, if you have voltage on all the coils, even if for a short time.

I reflowed the entire marked area on the motherboard (replaced the solder with leaded solder). For the past few days, the laptop has been working perfectly without any issues. On pin 27 of the KBC, there is a stable 3.36V every time.

I returned it to the client with the hope that it won't come back.

Machine, I want to sincerely thank you for your help!