HP 255 G4 Płyta ABL51 LA-C781P REV: 1.0 brak napięć

HP 255 G4

Płyta: ABL51 LA-C781P REV: 1.0
Procesor: AM6310ITJ44JB
Grafika: UMA
KBC: ene KB9022Q D

Witam!

Komputer bez śladów zalania nie reaguje w ogóle na podłączoną ładowarkę, nie ładuje baterii, nie świeci się dioda na gnieździe zasilania.
Brak zwarć na cewkach, brak zwarć na PQ4 i PQ5 , na PR20 obecne jest 19V.

Bardzo proszę o pomoc w znalezieniu usterki

Hello!

Measure the voltages to ground on pins 2, 4, 6, 11, 12, 13, 14, 15 of chip PU2.

Thank You for reply and sorry for my late respond.

PU2 Pin:

2 - 0 V
4 - 0 V
6 - 0 V
11 - 19,47 V
12 - 4,40 V
13 - 0 V
14 - 0 V
15 - 0 V

Measure the resistances to ground on pins 14, 15 of chip PU2.

PU2 pin:

14 - 35,5 Ohm
15 - 57,5 KOHm

soczek42 napisał(a):14 - 35,5 Ohm

It is a short circuit to ground on +5VL standby power rail.
Remove the chip PU2 from the board and remeasure the resistance to ground on pad 14 on the place of chip PU2. If the resistance will not change, perform a short circuit test described here on that pin. For a short circuit test limit the voltage to 5V (chip PU2 should be removed from the board during a short circuit test).

After remove PU2 on Pin 14 ressisantce to ground was changed - about 11 MOhm ad groving up. So should I replace PU2? I don't have schematic for this board, could You tell please what description have PU2 chip?

soczek42 napisał(a):After remove PU2 on Pin 14 ressisantce to ground was changed - about 11 MOhm ad groving up. So should I replace PU2?

Yes, chip PU2 is bad for sure. Replace it.

soczek42 napisał(a):I don't have schematic for this board, could You tell please what description have PU2 chip?

The schematic for that board is currently not available.
PU2 = Richtek RT8243AZQW

After replacing PU2 on the Pin14 I have only 0,5 V and the LED on the Lan port blinks

Remeasure the resistances to ground on pins 14, 15 of chip PU2.
If both resistances are high (in kΩ range or greater), remeasure the voltages suggested in post #2.

The resistances to ground on pins:
14 - 42,3 MOhm
15 - 62,5 KOhm

Voltages on pin:

2 - 0 V
4 - 0 V
6 - 0 V
11 - 0 V
12 - 0 V
13 - 0 V
14 - 0 ,49V
15 - all time change from 0 V to 0,39V and again 0 V and again 0,39V ( it happens quickly )

Measure the voltage to ground on resistor PR20 (it is located near the charger chip).

On PR20 on two side i have 0V. On PQ4 I have voltages:

1 ,2,3 - all time change from 0 V to 0,11562V
4 - all time change from 0 V to 0,20597V
5,6,7,8 - 19,34 V

Measure the resistance to ground on resistor PR20.
If the resistance is high (in kΩ range or greater), measure the voltages to ground on pins 3, 4, 5, 6, 11, 16, 17, 20 of PU1.

On PR20 i have 3,8 Ohm. I should perform a short circuit test ? but what voltage and current limit sholud I set?

soczek42 napisał(a):On PR20 i have 3,8 Ohm. I should perform a short circuit test ? but what voltage and current limit sholud I set?

First inspect the chip PU2 with surroundings for a solder bridge or anything else. Also check, if you solder the chip PU2 in correct orientation.

If everything seems ok, perform a short circuit test on resistor PR20. First try with voltage limit 1V, if it does not show anything, raise up the voltage limit to 3V.
You should start with low current limit, and gradually increase it as described in trainig section.

I checked the PU2 area, orientation (all was good), and finaly picked up the PU2 again and still had low resistance on the PR20 (about 3 OHM). I soldered PU2 to mainboard and made a short-circuit test.

When I set 3V and started with 1A (because on 1 V i can't find anything warm) I could finally set a maximum 1.4A. Warm elements which I felt were: hybrid UAPU1 (least warm), lan chip UL1, and PQ11 with coil PL7. The resistance I measured to ground on PL7 is 3 Ohm. PQ11 has no short circuits. When I unsoldered the PJ2 jumper on the coil side I have resistance: 1.26Ohm and on the other 2.32Ohm

Transistor PQ11 is probably bad. Check it.
Open the jumper PJ2 and measure the resistance to ground on both pins of that jumper.

After open the PJ2 jumper, on the coil side I have resistance: 1.26Ohm and on the other 2.32Ohm. Sholud I measure this ressistance after replacing or removing PQ11?

soczek42 napisał(a):After open the PJ2 jumper, on the coil side I have resistance: 1.26Ohm and on the other 2.32Ohm.

Both resistances are too low.
Transistor PQ11 is bad almost for sure, there is also a short circuit to ground on output side of that converter.
First perform a short circuit test on output side of jumper PJ2. Limit the voltage to 3V (jumper PJ2 should be opened during a short circuit test).