• Dell Latitude 7400 - brak podświetlenia po zalaniu

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#1 Dell Latitude 7400 - brak podświetlenia po zalaniu


by iT0mT0m 4 September 2025, 19:14
Witam,

Dostałem do sprawdzenia laptopa Dell Latitude 7400 (LA-G871P Rev 1.0), który został zalany przez deszcz wpadający przez okno (zostawiony przy oknie). Zalanie sięgało w okolicach pamięci RAM oraz gniazda LVDS (klient zgłaszał, że laptop działał normalnie, tylko nie było podświetlenia). Po oczyszczeniu i weryfikacji spalone były 2 bezpieczniki od podświetlenia. Mierząc rezystancje na obu końcach punktów lutowniczych bezpieczników nie stwierdzono niskich oporności co by świadczyło o zwarciu. Po wymianie bezpieczników podświetlenie matrycy wróciło. Po zrobieniu reinstalacji systemu laptop został zwrócony. Po kilku dniach laptop powrócił z tym samym problemem, czyli braku podświetlenia. Ponowna weryfikacja bezpieczników nie wykazała ich spalenia i po ponownym skręceniu laptopa podświetlenie wróciło. Laptop był testowany kilka godzin i nie było żadnych objawów. Znów po pewnym czasie został zwrócony na brak podświetlenia. Czym to może być spowodowane?

Re: Dell Latitude 7400 - brak podświetlenia po zalaniu


by Google Adsense [BOT] 4 September 2025, 19:14

#2 Re: Dell Latitude 7400 - brak podświetlenia po zalaniu


by matic 4 September 2025, 21:34
Hello!

Please, post clear pictures of flooded areas of the board in its current state.

#3 Re: Dell Latitude 7400 - brak podświetlenia po zalaniu


by Vogelek23 6 September 2025, 12:12
Otwórz obudowę matrycy i - oczywiście po odłączeniu baterii głównej - sprawdź, czy gniazdo lub wtyk kabla matrycy od strony ekranu nie są skorodowane.

iT0mT0m wrote:spalone były 2 bezpieczniki od podświetlenia
Dwa? :wtf: To znaczy które konkretnie (Fxx)? Bo od podświetlenia jest na tej płycie tylko jeden bezpiecznik.

#4 Re: Dell Latitude 7400 - brak podświetlenia po zalaniu


by iT0mT0m 6 September 2025, 12:46
matic wrote:Hello!

Please, post clear pictures of flooded areas of the board in its current state.

Image
Image
Image

Nie było tutaj konkretnie, aby woda stała czy coś tylko były lekkie zacieki w tym obszarze. Ciecz dotarła nawet do jednej z kości pamięci RAM, ale o dziwno działa poprawnie.

Vogelek23 wrote:Otwórz obudowę matrycy i - oczywiście po odłączeniu baterii głównej - sprawdź, czy gniazdo lub wtyk kabla matrycy od strony ekranu nie są skorodowane.

Nie było nic skorodowane. Prewencyjnie przeczyściłem gniazda, aby mieć pewność, że nic tam nie było.

Vogelek23 wrote:Dwa? To znaczy które konkretnie (Fxx)? Bo od podświetlenia jest na tej płycie tylko jeden bezpiecznik.

Spalony był FV1 +BL_PWR_SRC oraz FV2 +TS_PWR. Napisałem dwa, ponieważ obydwa idą do gniazda matrycy wg boardview.

#5 Re: Dell Latitude 7400 - brak podświetlenia po zalaniu


by Vogelek23 6 September 2025, 13:31
Podstaw 100% sprawną, przetestowaną matrycę.

#6 Re: Dell Latitude 7400 - brak podświetlenia po zalaniu


by iT0mT0m 6 September 2025, 18:07
Niestety takiej nie posiadam. Musiałbym zamówić. Mogę coś jeszcze sprawdzić zanim bym ją zamawiał?

#7 Re: Dell Latitude 7400 - brak podświetlenia po zalaniu


by matic 7 September 2025, 18:16
Measure the voltages to ground on the following points, when the machine is turned on with the internal matrix connected:
- On pin 2 of resistor RC2.
- On pin 2 of fuse FV1.
- On pin 1 of coil LV1.
- On pin 1 of diode DV2.

#8 Re: Dell Latitude 7400 - brak podświetlenia po zalaniu


by iT0mT0m 14 September 2025, 10:47
matic wrote:Measure the voltages to ground on the following points, when the machine is turned on with the internal matrix connected:
- On pin 2 of resistor RC2.
- On pin 2 of fuse FV1.
- On pin 1 of coil LV1.
- On pin 1 of diode DV2.


RC2 pin 2 - After connect power supply 2.5V. After power on button voltage is 0.016V.
FV1 pin 2 - After connect power supply 13.5V. After power on button voltage is get down.
LV1 pin 1 - Always 0V. Once after power on button voltage is 1.074V.
DV2 pin 1 - 0V after power on.

#9 Re: Dell Latitude 7400 - brak podświetlenia po zalaniu


by matic 14 September 2025, 12:32
Measure the voltages to ground on pins 1, 2 of transistor QV2, when the machine is turned on with the internal matrix connected.
Transistor QV2 pinout:
Image

#10 Re: Dell Latitude 7400 - brak podświetlenia po zalaniu


by iT0mT0m 14 September 2025, 12:43
QV2 pin 1 - before power on - 13.1V, after power on - 0V
QV2 pin 2 - before power on - 0V, after power on - 3.3V

#11 Re: Dell Latitude 7400 - brak podświetlenia po zalaniu


by matic 15 September 2025, 08:34
Measure the voltages to ground on pins 1, 3, 4 of transistor QV1, when the machine is turned on with the internal matrix connected.

#12 Re: Dell Latitude 7400 - brak podświetlenia po zalaniu


by iT0mT0m 15 September 2025, 17:23
matic wrote:Measure the voltages to ground on pins 1, 3, 4 of transistor QV1, when the machine is turned on with the internal matrix connected.


QV1 pin:
1 - 13.5V
3 - 2.007V
4 - 13.5V

#13 Re: Dell Latitude 7400 - brak podświetlenia po zalaniu


by matic 16 September 2025, 07:56
Remeasure the voltages suggested in post #7, when the machine is turned on with the internal matrix connected.

#14 Re: Dell Latitude 7400 - brak podświetlenia po zalaniu


by iT0mT0m 18 September 2025, 19:29
matic wrote:Remeasure the voltages suggested in post #7, when the machine is turned on with the internal matrix connected.

- On pin 2 of resistor RC2 2,505V
- On pin 2 of fuse FV1 - 13,51V
- On pin 1 of coil LV1 - 1,174V
- On pin 1 of diode DV2 - 0,639V

#15 Re: Dell Latitude 7400 - brak podświetlenia po zalaniu


by matic 19 September 2025, 15:53
- Set your multimeter to the diode mode range and measure the voltage drops to ground on all pins of diode DV2 with the positive (red) probe connected to ground.
- Measure the voltages to ground on pins 2, 3 of diode DV2, when the machine is turned on with the internal matrix connected.

Diode DV2 pinout:
Image

#16 Re: Dell Latitude 7400 - brak podświetlenia po zalaniu


by iT0mT0m 20 September 2025, 20:38
matic wrote:- Set your multimeter to the diode mode range and measure the voltage drops to ground on all pins of diode DV2 with the positive (red) probe connected to ground.

1 - 0.018V
2 - 0.760V
3 - 0.804V

matic wrote:- Measure the voltages to ground on pins 2, 3 of diode DV2, when the machine is turned on with the internal matrix connected.

2 - 0.002V
3 - 1.058V
Measured while show image on screen without backlight.

#17 Re: Dell Latitude 7400 - brak podświetlenia po zalaniu


by matic 22 September 2025, 08:29
Also measure the resistance to ground on pin 1 of diode DV2 with the internal matrix connected.

#18 Re: Dell Latitude 7400 - brak podświetlenia po zalaniu


by iT0mT0m 22 September 2025, 21:32
matic wrote:Also measure the resistance to ground on pin 1 of diode DV2 with the internal matrix connected.

14.8Ω

#19 Re: Dell Latitude 7400 - brak podświetlenia po zalaniu


by matic 23 September 2025, 09:35
This resistance is way too low.
It's most likely caused by a damaged LCD matrix or LVDS cable.

Remeasure this resistance with the LVDS cable disconnected from the board. If the resistance increases to a high value (in the kΩ range or greater), measure the resistance again with the LVDS cable connected and LCD matrix disconnected.
If the resistance with LCD matrix disconnected and LVDS cable connected is still high (in kΩ range or greater), the LCD matrix is definitely damaged and needs to be replaced.

#20 Re: Dell Latitude 7400 - brak podświetlenia po zalaniu


by iT0mT0m 23 September 2025, 19:54
Without LVDS cable I have 14.9Ω resistance on pin 1 of DV2.

Re: Dell Latitude 7400 - brak podświetlenia po zalaniu


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