Sony vaio PCG-71911m (Main Mbx-247 no power, no led)

Good afternoon friends of the forum. This laptop has the problem that it does not turn on, no LEDs (the LEDs flash very quickly after powering up and turn off immediately)
Taking some measurements I find the voltage of 3.3V on the PL13 coil but 0v on the PL14 coil.
Measuring the resistance on the PL14 coil I find 35 ohm. If I disconnect the power supply, the resistance rises to 30kohm.
I turn the card over and I find liquid damage, a little scattered oxidation. I clean the card well, re-weld the PU9 around it, replace PU13 because I find it a little blackened. I replace an interrupted resistance PR113.
Now after this cleaning I no longer have the voltage of 3.3v, practically on the drain of PQ31 I have no voltage. On the gate I find 19.7V and on the source 19.7V
Doing a resistance test between drain and ground I find 50Kohm.

PU10 Measurement voltage
pin 1 0v
pin 2 3,58v
pin 3 3,18v
pin 4 0v
pin 5 0v
pin 6 0v
pin 7 0v
pin 8 0v
pin 9 0v
pin 10 0v
pin 11 0v
pin 12 0v
pin 13 4,67v
pin 14 0v
pin 15 0v
pin 16 0v
pin 17 0v
pin 18 0v
pin 19 0v
pin 20 0v
pin 21 5,08v
pin 22 19,08v
pin 23 0v
pin 24 0v
pin 25 4,78v
pin 26 5,07v
pin 27 0v
pin 28 0,09v

Hello.

robgerr napisał(a):Measuring the resistance on the PL14 coil I find 35 ohm. If I disconnect the power supply, the resistance rises to 30kohm.

Do not measure resistance on main board with connected power supply or battery. Doing resistance measurements when power is applied to the board may cause multimeter damage or even board damage in worst case.

robgerr napisał(a): I clean the card well, re-weld the PU9 around it, replace PU13 because I find it a little blackened. I replace an interrupted resistance PR113.

All elements affected by liquid damage and corrosion should be replaced with new/working ones.
Measure the power consumption of the main board in stand by.
Have you tried to program the BIOS chip with a working BIOS file?

Measure the voltages on all pins of PQ31, PD18.

All elements affected by liquid damage and corrosion should be replaced with new/working ones

thanks xamledyD.
I have substitute and coponents I had. The resistance test I made it clearly by disconnecting the power supply because I know it risks burning the multimeter.
I didn't do the bios test because I believe that the always 3v and 5v voltages are missing, the bios has nothing to do with it

Measure the voltages on all pins of PQ31, PD18.

Thank's Machine

Measure the voltages to ground on all pins of transistors PQ3, PQ5.

Also measure the resistance to ground on any pin of resistor PR155.

Thank's Matic
PQ3:
pin 1 0v
pin 2 9,3v
pin 3 0v
pin 4 0v
pin 5 0v
pin 6 0v

PQ5:
pin 1 19,74V
pin 2 0v
pin 3 0v
pin 4 0v
pin 5 0v
pin 6 19,74v

PR155 REsistence to ground 50 Kohm

Remove the transistor PQ3 from the board and check, if you get 19V on resistor PR155.

Remove the transistor PQ3 from the board and check, if you get 19V on resistor PR155.

Removed PQ3 but no 19v on the resistor PR155

Unplug PQ5 and measure if you have a voltage on PR155. PQ5 must be short

Unplug PQ5 and measure if you have a voltage on PR155. PQ5 must be short

removed also pq5 is now on pr155 I have the 19V. Q3 I didn't put it back. Now on PL13 I find 3.3V but on PL14 0V

Measure the voltages to ground on pads 2, 5 on the place of transistor PQ3. Transistors PQ3 and PQ5 should be removed from the board during the measurements.

Measure the resistance between pins 1, 6 of the transistor PQ5 itself out of the board.

Measure the voltages to ground on pads 2, 5 on the place of transistor PQ3. Transistors PQ3 and PQ5 should be removed from the board during the measurements.

Pad 2 9,3V
Pad 5 11,62V

Measure the resistance between pins 1, 6 of the transistor PQ5 itself out of the board.

Resistence Start From 1,80Mohm and slowly dropt after one minue to 120KOhm

Measure the voltages to ground on pins 3, 5 on the place of transistor PQ5. Transistors PQ3 and PQ5 should be removed from the board during the measurements.

Measure the voltages to ground on pins 3, 5 on the place of transistor PQ5. Transistors PQ3 and PQ5 should be removed from the board during the measurements.

Pad 3 0v
Pad 5 0v

Solder the transistor PQ5 back to the place and remeasure the voltages to ground on all pins of PQ5. Transistor PQ3 should be removed from the board during the measurements.

Pin 1 19,67v
Pin 2 0v
Pn 3 0v
pin 4 0V
pin 5 0V
pin 6 19,74V

Check, if the RTC battery is good (it should have at least 2.9V).

If so, measure the voltages to ground on pins 2, 4, 5 of chips PU3, PU4 and PU5.
Also measure the resistance to ground on pin 3 of transistor PQ5.

Check, if the RTC battery is good (it should have at least 2.9V)

Battery Voltage 3,09V
PU3:
pin 2 2,85V
Pin 4 0v
pin 5 2,84v
PU4:
pin 2 0v
pin 4 2,84V
pin 5 2,84V

PU5:
Pin 2 2,83V
pin 4 0v
pin 5 2,84v
Pq5 pin 3 resistance 90 ohm

Measure the resistance to ground on pad 3 on the place of transistor PQ5, when the transistors PQ3, PQ5 are removed from the board.

Measure the resistance to ground on pad 3 on the place of transistor PQ5, when the transistors PQ3, PQ5 are removed from the board.

Same resistence, 90 Ohm