Acer Nitro AB515-55-77MM LA-J891P zwarcie na PRB3 PRB46

Cześć,

Mam na stole obecnie laptopa jak w temacie z obsadą:
I7-10750H
RTX2060
KBC KB9022Q
SRJAU

Z pomiarów wynika, że mam zwarcie na PRB3 1,7Ohm
PLZ1-PLZ4 rezystancja 2.2 ohm
PLG1 5 ohm
PLV2-PLV4 0,4 ohm (rezystancja raczej ok? jak dla rtx2060?)
8n. układu SPI rezystancja w K Ohm

Brak jakichkolwiek napięć, nie ładuje baterii.

Wylutowałem PRB3 oraz PRB46 i zwarcie występuję na prawym padzie od strony zasilania CPU.
Wykonałem próbę zwarciową z ograniczeniem do 1V , przy napięciu 1V pobór wynosi 1,5A jednak nie mogę zlokalizować miejsca zwarcia. Nie mam kamery termowizyjnej, ipa nie pokazuje nic ani sprężone powietrze...

Badając organoleptycznie, jedyne miejsce które wyczułem delikatnie cieplejsze to okolice zaznaczone na zdjęciu, ta gruba linia zasilająca.


Nie byłem pewny, czy mogę zwiększyć napięcie w tej linii.
Sprawdzałem rezystancje PRB3 względem wszystkich cewek i jedynie niska rezystancja była przy zasilaniu CPU ok 1,7 Ohm.

Gdzie jeszcze mogę sprawdzić możliwe miejsca zwarcia? Lub czy mogę zwiększyć napięcie podczas próby zwarciowej?

Z góry dziękuję za podpowiedzi

LukaszBsKrakow napisal/-a:Sprawdzałem rezystancje PRB3 względem wszystkich cewek i jedynie niska rezystancja była przy zasilaniu CPU ok 1,7 Ohm.

Hello!
I don't understand exactly what you mean by that.
However, specify the resistances on all coils measured in reference to the shorted pin of resistor PRB3.

Hey Matic,
The resistance against PRB3 is:

PLZ 1-PLZ 4 3.8 ohms
PLG1 8 ohms
PLV2-PLV4 1.8 ohm
PL1101 82 ohms
PL301 1.5K ohms
PL501 5k ohms
PL1801 4k ohms
PLB2 50k ohms
PLW1 63 ohms
PLW2 63 ohms
PLM1 320 ohms
PLH1 55 ohms
PLA1 21 ohms

Remove the resistor PRV75 from the board and remeasure the resistance to ground on the shorted pin of resistor PRB3.

After desoldering, the resistance on the PRB3 contact is 8M ohm.

Does this mean the GPU is dead?

LukaszBsKrakow napisal/-a:Does this mean the GPU is dead?

No, it means that one of the DrMOS chips PUV2, PUV3, PUV4 or PUV9 is damaged, but the GPU chip may be consequently damaged as well.

Solder the resistor PRV75 back to its place and remove the coils PLV2, PLV3, PLV4 and PLV13 one by one from the board. Check the resistance to ground on the shorted pin of resistor PRB3 after removing each of the coil.
After you remove the right coil the resistance to ground on the resistor PRB3 should increase to a high value. When this happens, stop with removing the coils.
It means that the DrMOS chip located right near this coil is damaged.

Okay, and if I find a broken drmos and remove it from the board, can I try to start the laptop? on intel graphics it should boot?

LukaszBsKrakow napisal/-a:Okay, and if I find a broken drmos and remove it from the board, can I try to start the laptop?

Yes, you can, but you should solder the other removed coils back to the board.
You may also need to replace a damaged DrMOS, as without it the board may not work. But you can try without it first.

LukaszBsKrakow napisal/-a:on intel graphics it should boot?

I'm not 100% sure, but in case the GPU is damaged, there will most likely be no picture on the screen.

I removed all the coils in turn, measuring the resistance to ground on PRB3.

Effect? I don't have any coil on the GPU and the short circuit is still there...

In addition, on the pads from the DrMOS side I have a resistance of 330k ohm, while from the GPU side 0.5 ohm

In this case perform a short circuit test on pin 4 of resistor PRV75 (no need to remove the resistor PRV75 from the board).
Start with a voltage limit 1V. If nothing heats up, rise up the voltage limit to 3V. If still nothing, rise up the voltage limit to 5V.
But if you exceed 1V, the coils PLV2, PLV3, PLV4 and PLV13 must be removed from the board. Make sure to use enough thick test wires (with a cross section at least 1mm^2).

One of the DrMOS transistors, or one of the filter capacitors on 19V power rail near them is damaged.

I have all the coils removed, so I'll start with 1V and see if after reaching 5V there is still nothing visible, I will reinstall the coils and do a short circuit test with a 1V limit.

Do I understand correctly?

EDIT: Bingo, damaged capacitor at DrMOS.

I don't have one in stock, can I try to run the disc without it or install a replacement?

LukaszBsKrakow napisal/-a:EDIT: Bingo, damaged capacitor at DrMOS.
I don't have one in stock, can I try to run the disc without it or install a replacement?

Which capacitor exactly?

In the diagram, it is marked as PCV90

I have a similar one from the donor motherboard with the designation 10u/25v_8

Will be OK?

LukaszBsKrakow napisal/-a:In the diagram, it is marked as PCV90

Yes, for the test you can run the board without this capacitor.

LukaszBsKrakow napisal/-a:I have a similar one from the donor motherboard with the designation 10u/25v_8
Will be OK?

Yes, you can use it.

Ok, I filled in the missing capacitor. The laptop started up, all tests passed. The equipment was returned to the customer.

Thank you very much my friend matic for helping me to solve the problem.