Dell Vostro 1550 - 5V_S0 is enabled always

[IamPritesh]

I have this strange issue where the HDD, ODD gets powered even when the system is in shutdown state. To be more specific the S0 state 3 volt and 5 volt are enabled as soon as ac adapter is plugged in. Ideally it should only be enabled after power-on.

I am confused as to what is causing the auto enable of S5-s0 state specially for 5v and 3V . I have checked the mosfets u3601 and u3602 and they are not bad. The gate pin has around 7V .

..I am attaching the schematic just in case anyone wants to shed some light on this.

PS- The system does start fine and works fine. But after shutdown the battery gets drained out even in shutdown mode.

[piernov]

Re: Dell Vostro 1550 - 5V_S0 is enabled always

Voltage on all pins of Q3602 when off?

[IamPritesh]

Re: Dell Vostro 1550 - 5V_S0 is enabled always

Voltage on all pins of Q3602 when off?

Thanks for responding. I can access to the board tomorrow. So that's a wait period of 10 hours unfortunately. To save some valueable time, can you please post the voltages it should ideally have for Q3602 and I will check as soon as I can .

[mcplslg123]

Re: Dell Vostro 1550 - 5V_S0 is enabled always

Q3602 is 2 n channel fets combined in one package where pin1-2-6 is one fet and pin 4-5-3 is another. Your problem is RUN_ENABLE is high on pin3. It should be low in off condition. If you look at pin 4-5-3 part of fet then this is how it should work

pin5 gate-must be high. N channel fet will pass current from Source to Drain when gate is high. So you have either no voltage or very low voltage on gate pin5. As far as my understanding is concerned, you should get voltage only on pin5 & 6 in off condition. Then it will work as intended.

Since you have low or no voltage on gate pin5, ground (pin4) is not travelling from source to Drain(pin3) making RUN_Enable go high.

[IamPritesh]

Re: Dell Vostro 1550 - 5V_S0 is enabled always

Q3602 is 2 n channel fets combined in one package where pin1-2-6 is one fet and pin 4-5-3 is another. Your problem is RUN_ENABLE is high on pin3. It should be low in off condition. If you look at pin 4-5-3 part of fet then this is how it should work

pin5 gate-must be high. N channel fet will pass current from Source to Drain when gate is high. So you have either no voltage or very low voltage on gate pin5. As far as my understanding is concerned, you should get voltage only on pin5 & 6 in off condition. Then it will work as intended.

Since you have low or no voltage on gate pin5, ground (pin4) is not travelling from source to Drain(pin3) making RUN_Enable go high.

Thanks. The pin details are as follow :

Pin1 - GND
Pin 2 - 0V
Pin 3 - 12V
Pin 4 - GND
Pin 5 - 1.2 V
Pin 6 - 1.2 V



Pin 1 - 0v
pin 2 -

[piernov]

Re: Dell Vostro 1550 - 5V_S0 is enabled always

Check voltage on both sides of R3606, check resistance across R3606.

[IamPritesh]

Re: Dell Vostro 1550 - 5V_S0 is enabled always

Check voltage on both sides of R3606, check resistance across R3606.

r3606 voltage on input side is 3.3 volt and output end has 1.2 volt. Havent checked the resistance

[dellxps15]

Re: Dell Vostro 1550 - 5V_S0 is enabled always

do you have some usb charging option in bios ?

[IamPritesh]

Re: Dell Vostro 1550 - 5V_S0 is enabled always

do you have some usb charging option in bios ?

No such option . WAKE up on LAN is also disabled.

[dellxps15]

Re: Dell Vostro 1550 - 5V_S0 is enabled always

dunno if on sandy bridge 5v and 3v always are present only after power on. battery is attached to system ?

[IamPritesh]

Re: Dell Vostro 1550 - 5V_S0 is enabled always

dunno if on sandy bridge 5v and 3v always are present only after power on. battery is attached to system ?

The power sequence clearly shows that 5V_S0 should be high only after laptop powered on .

R3606 has 3.3 and 1.2V reading. Does that sound OK ?

[mcplslg123]

Re: Dell Vostro 1550 - 5V_S0 is enabled always

R3606 READING IS DEFINITELY WRONG.It should be 3.3V on both sides. Is that resistor 100K?? Take it out of circuit and check. Do check Q3603

[IamPritesh]

Re: Dell Vostro 1550 - 5V_S0 is enabled always

R3606 READING IS DEFINITELY WRONG.It should be 3.3V on both sides. Is that resistor 100K?? Take it out of circuit and check. Do check Q3603

Resistor is fine. It shows a reading of 99.5K ohms when taken out of the circuit. I will check Q3603 shortly.

[piernov]

Re: Dell Vostro 1550 - 5V_S0 is enabled always

Any of Q3602, Q3603, Q3701, Q3704 could be pulling it low. R3606 is a very weak pull-up of 100k, so the "short to ground" will also be somewhere around 60k so it'll be hard to measure. You can try removing these transistors one by one and see if PS_S3CNTRL comes back to 3.3V.
Of course make sure there's no dirt or corrosion on the board since it could cause this kind of problem as well.

[IamPritesh]

Re: Dell Vostro 1550 - 5V_S0 is enabled always

Any of Q3602, Q3603, Q3701, Q3704 could be pulling it low. R3606 is a very weak pull-up of 100k, so the "short to ground" will also be somewhere around 60k so it'll be hard to measure. You can try removing these transistors one by one and see if PS_S3CNTRL comes back to 3.3V.
Of course make sure there's no dirt or corrosion on the board since it could cause this kind of problem as well.

Thanks for your suggestion. Will try it soon and update the results here