dell vostro 3450 was turning off ac adaptor. I fixed it but it can´t turn on yet

[alan_aguinaga]

Hi Guys! How are you?

I´m trying to fix Dell´s Vostro 3450 motherboard model Dav02amb8f1 with VGA ATI.

My note was working well and then suddenly it turned off. When I tried to power it on again it started to shut down ac adaptor.

I did a circuitry analysis on motherboard and I discovered mosfet PQ 36 was shorted. I swap this mosfet and AC Adaptor stopped to being turn off. Nice! I thought that problem was fixed but my board still not working. Any sign of turn on sequence is noted now.

I´m using adjustable font to feed it and I discovered now mosfet channel P named pq31 has 0 V in gate and 19 V on drain and source.

https://photos.app.goo.gl/i7hAubRFpbQSRm9R6

I really don´t know what next step to verify on this board. I don´t know exactly why PQ31´s gate has 0V and if it is correct or if it must have about 3 V to turn this board on.

Does it ACAV_IN is signing OK to PQ3? What is the logic behind ACAV_IN? Is it a way to short to ground to avoid damages?

You can check schematic PQ31 belongs on page 44.

I´ve checked U1 VCC and it has a correcct tension?

Could anyone help me to solve this problem?

https://cdn.badcaps-static.com/pdfs/...e6e012530e.pdf

[Techtiger]

Re: dell vostro 3450 was turning off ac adaptor. I fixed it but it can´t turn on yet

Teste the Voltage on all pins of PU1 charging IC , PQ31 Gate must be +3 to +10V to bypass the voltage, PQ3 FET pin 2 must be active high to pin 1&3 go GND ,Two resistors connected to that line PR13/14 is your Voltage divide , find out PS_ID Voltage also

[piernov]

Re: dell vostro 3450 was turning off ac adaptor. I fixed it but it can´t turn on yet

I'm a bit confused about the measurements, as if PQ31 has 19V on source then gate must be either 19V (in case MOSFET is shorted) or 1.7V (due to the voltage divider).
Anyway, if you have 19V getting to +PWR_SRC it should be ok.

[alan_aguinaga]

Re: dell vostro 3450 was turning off ac adaptor. I fixed it but it can´t turn on yet

I'm a bit confused about the measurements, as if PQ31 has 19V on source then gate must be either 19V (in case MOSFET is shorted) or 1.7V (due to the voltage divider).
Anyway, if you have 19V getting to +PWR_SRC it should be ok.

Yes, I´m getting 19 V from both sides. But 0,01 V on pin4 (gate)

[alan_aguinaga]

Re: dell vostro 3450 was turning off ac adaptor. I fixed it but it can´t turn on yet

Teste the Voltage on all pins of PU1 charging IC , PQ31 Gate must be +3 to +10V to bypass the voltage, PQ3 FET pin 2 must be active high to pin 1&3 go GND ,Two resistors connected to that line PR13/14 is your Voltage divide , find out PS_ID Voltage also

I´ll do that ASAP. thanx! I´ll give you feedback later.

[alan_aguinaga]

Re: dell vostro 3450 was turning off ac adaptor. I fixed it but it can´t turn on yet

Teste the Voltage on all pins of PU1 charging IC
https://photos.app.goo.gl/G8PkNCrjKNkBxVqJ8


PQ31 Gate must be +3 to +10V to bypass the voltage

gate pin 4 - 0,00 V


PQ3 FET pin 2 must be active high to pin 1&3 go GND ,

PQ3 gate 3 v, source e drain 0 V


Two resistors connected to that line PR13/14 is your Voltage divide , find out PS_ID Voltage also

PR13/14 - no voltage but both ok passing resistance measurements

[piernov]

Re: dell vostro 3450 was turning off ac adaptor. I fixed it but it can´t turn on yet

If you get 19V on PQ31 source then you should be getting 19V too on CSSN/CSSP.

[alan_aguinaga]

Re: dell vostro 3450 was turning off ac adaptor. I fixed it but it can´t turn on yet

on power sw I got 2,35 on pin 2 and 3

[Techtiger]

Re: dell vostro 3450 was turning off ac adaptor. I fixed it but it can´t turn on yet

Teste the Voltage on all pins of PU1 charging IC
https://photos.app.goo.gl/G8PkNCrjKNkBxVqJ8
PQ31 Gate must be +3 to +10V to bypass the voltage
gate pin 4 - 0,00 V
PQ3 FET pin 2 must be active high to pin 1&3 go GND ,
PQ3 gate 3 v, source e drain 0 V
Two resistors connected to that line PR13/14 is your Voltage divide , find out PS_ID Voltage also
PR13/14 - no voltage but both ok passing resistance measurements

As PIERNOV said bit confused about the measurements PQ31( test if PQ31 is short ) has 19V on source either PQ31 short, as for the Schematic voltage divider 10k & 100k 1.7V to Gate strange !
CN3 DC jack connector pin 1 is ypur PS ID what is the voltage ?
required voltages for PU1 are not full fill pin 21 26 27 28 ect
test continuity between PR147 to pin 27 28 PU1

I'm a bit confused about the measurements, as if PQ31 has 19V on source then gate must be either 19V (in case MOSFET is shorted) or 1.7V (due to the voltage divider).
Anyway, if you have 19V getting to +PWR_SRC it should be ok.

[alan_aguinaga]

Re: dell vostro 3450 was turning off ac adaptor. I fixed it but it can´t turn on yet

As PIERNOV said bit confused about the measurements PQ31( test if PQ31 is short ) has 19V on source either PQ31 short,

as for the Schematic voltage divider 10k & 100k 1.7V to Gate strange !

CN3 DC jack connector pin 1 is ypur PS ID what is the voltage ?


required voltages for PU1 are not full fill pin 21 26 27 28 ect
test continuity between PR147 to pin 27 28 PU1

________________________________________

I will do this tests on those pins later but a have same impressions about soldering on PQ31 cause it is too complicated to reach.

Both of you are correct. He gives me a right clue about tension on pins 27 and 28.

I tested PQ31 outside board before soldering it back again and now pin 4 (gate) has 19 v. It means exactly what you said. It is shortened. I will replace it later and give you feedback.

Thanxx for you clues!

[alan_aguinaga]

Re: dell vostro 3450 was turning off ac adaptor. I fixed it but it can´t turn on yet

I placed PQ31 better and it´s gate now provide 1,8 V. But now I think PU1 is damaged. It is heating and PR25 is hot too. It is connected to pin 22 (DC In).

I think I need to replace PU1 too. Any considerations about it?

[Techtiger]

Re: dell vostro 3450 was turning off ac adaptor. I fixed it but it can´t turn on yet

First test all components in that line 3 resistance & 2 Caps (DC_IN_SS =+19V) Check
PC 19 if it’s short to GND both sides