Dead acer 7750g

[giulio93]

Hi everyone, I am passionate about mobo repair. I have this acer stone dead. I mesure the V at all the coils and I have the 5V and the 3.3V ad the bottom of the board. all the other voltage (exept the 19,5V and a "strange" 17,95V on one of the power button pin and 0,733 on some mosfet's surce ) are missing. I mesure in resistence mode all the coils and this are the results: 340, 25, 2.5, 15.7 (x2), 14.8, 394, 6K, 30K, 7M. Where should I start looking at?
Thank you very very much

[mon2]

Re: Dead acer 7750g

Start with the schematic -> search for 'charger' = PU2.

Then review the first 2 mosfets, starting with the one that mates with the external DC adapter.

Remove all power & no battery.

Meter in resistance mode (2k scale).

Check if either of the first 2 mosfets is damaged by checking the resistance of:

source & drain
source & gate
gate & drain

looking for a low resistance which often means the mosfet is defective and must be replaced. If the resistance is OK then using ONLY the adapter, check how far the Vin travels onto the logic board.

Voltage @ B+ junction ?

Carefully measure the voltages on PU2. Post your readings.

NB: More in depth details on this process are posted up above by @Piernov:

https://www.badcaps.net/forum/showthread.php?t=90356

Definitely recommended reading.

[giulio93]

Re: Dead acer 7750g

Start with the schematic -> search for 'charger' = PU2.

Then review the first 2 mosfets, starting with the one that mates with the external DC adapter.

Remove all power & no battery.

Meter in resistance mode (2k scale).

Check if either of the first 2 mosfets is damaged by checking the resistance of:

source & drain
source & gate
gate & drain

looking for a low resistance which often means the mosfet is defective and must be replaced. If the resistance is OK then using ONLY the adapter, check how far the Vin travels onto the logic board.

Voltage @ B+ junction ?

Carefully measure the voltages on PU2. Post your readings.

NB: More in depth details on this process are posted up above by @Piernov:

https://www.badcaps.net/forum/showthread.php?t=90356

Definitely recommended reading.

The resistances in th mosfets are around 2-300K or 0L. The 19,39V comes out the second mosfet through the sensor resistor and go on.
The V at the PU2 are: from 1 to 24:
5,1
1,39
0,001-0,010
0,043
0,010
0
0-0,010
2,39
0
0,397
0,125
GND
GND
0
5,1
4,985
0,735
0,735
19,39
19,38
0,735
0,730
0,005
18,99

[giulio93]

Re: Dead acer 7750g

Start with the schematic -> search for 'charger' = PU2.

Then review the first 2 mosfets, starting with the one that mates with the external DC adapter.

Remove all power & no battery.

Meter in resistance mode (2k scale).

Check if either of the first 2 mosfets is damaged by checking the resistance of:

source & drain
source & gate
gate & drain

looking for a low resistance which often means the mosfet is defective and must be replaced. If the resistance is OK then using ONLY the adapter, check how far the Vin travels onto the logic board.

Voltage @ B+ junction ?

Carefully measure the voltages on PU2. Post your readings.

NB: More in depth details on this process are posted up above by @Piernov:

https://www.badcaps.net/forum/showthread.php?t=90356

Definitely recommended reading.

Do you read any wrong values in the chip voltage?

[giulio93]

Re: Dead acer 7750g

I have other questions/doubt. I mesure the B+ at the surce of the cpu mosfet and it's present but dont go through it and comes to the coil. I also measure the PU7 (power chip that should be power the PCH I think) and it comes the 5V but nothing comes out. For ram and vga it's the same, the power comes to the power chip but nothing come out.
Another question in. Which voltage should I have at power off pc?

[mon2]

Re: Dead acer 7750g

Pin 3 reading is not correct. This is the EN (enable) pin for PU2.

This signal is driven by KB930QF (U21) and then enters the 0 ohm resistor @ PR31.

Confirm the voltage on pin # 2 of PR31 and then again on pin # 1 of PR31.

Is it 0v on both legs of PR31 ?

If yes, the KB930QF (U21) needs to be reviewed.

[giulio93]

Re: Dead acer 7750g

Pin 3 reading is not correct. This is the EN (enable) pin for PU2.

This signal is driven by KB930QF (U21) and then enters the 0 ohm resistor @ PR31.

Confirm the voltage on pin # 2 of PR31 and then again on pin # 1 of PR31.

Is it 0v on both legs of PR31 ?

If yes, the KB930QF (U21) needs to be reviewed.

All this voltages have to be present also at power of pc? If you could reply at my previuos answers you make my day and expand my knowledge. In the meantime I will measure the values you told me

[giulio93]

Re: Dead acer 7750g

Pin 3 reading is not correct. This is the EN (enable) pin for PU2.

This signal is driven by KB930QF (U21) and then enters the 0 ohm resistor @ PR31.

Confirm the voltage on pin # 2 of PR31 and then again on pin # 1 of PR31.

Is it 0v on both legs of PR31 ?

If yes, the KB930QF (U21) needs to be reviewed.

Bot legs of PR31 is 0V. The U21 is the super io?

[mon2]

Re: Dead acer 7750g

For PU7, see attached. It is a buck regulator that will accept a higher voltage and lower it to another required voltage. Often such regulators are based on a FB (feedback) pin which will use 2 resistors as a voltage divider to dial up the desired voltage for the output.

Review the ENable pin # 5 - what is the voltage reading there.

Expecting a logic high here to ENABLE this regulator.

If you see a logic high for the ENABLE and you also have a +5ALW rail present yet the regulator is not working, then review if the output rail is being shorted and causing an excessive current draw which will then cause this part to shut off, for safety.

For this review, remove all power, meter in resistance mode (2k scale) -> check the resistance to ground of the output coil. What is the resistance ?

If it is very low, then there may be a bad cap on this rail causing the excessive current draw. More after you post the readings.

Repeat for other rails that are not powering on.

If the ENABLE is NOT a logic high (~3v or higher), then the upstream circuit that operates the enable pin must be reviewed.

I measure the B+ at the source of the cpu mosfet and it's present but dont go through it and comes to the coil.

Which mosfet exactly ? Likely similar to the above - check if the enable pin is active or not. Also check the resistance to ground of the output coil (with NO power to the board).

[giulio93]

Re: Dead acer 7750g

For PU7, see attached. It is a buck regulator that will accept a higher voltage and lower it to another required voltage. Often such regulators are based on a FB (feedback) pin which will use 2 resistors as a voltage divider to dial up the desired voltage for the output.

Review the ENable pin # 5 - what is the voltage reading there.

Expecting a logic high here to ENABLE this regulator.

If you see a logic high for the ENABLE and you also have a +5ALW rail present yet the regulator is not working, then review if the output rail is being shorted and causing an excessive current draw which will then cause this part to shut off, for safety.

For this review, remove all power, meter in resistance mode (2k scale) -> check the resistance to ground of the output coil. What is the resistance ?

If it is very low, then there may be a bad cap on this rail causing the excessive current draw. More after you post the readings.

Repeat for other rails that are not powering on.

If the ENABLE is NOT a logic high (~3v or higher), then the upstream circuit that operates the enable pin must be reviewed.



Which mosfet exactly ? Likely similar to the above - check if the enable pin is active or not. Also check the resistance to ground of the output coil (with NO power to the board).

The pin 5 of the pu7 is 0V so is not high i supposed. The mosfet i'm speaking about is the PQ109 and 113, and also here the gate is at 0. If I understand well this gate will be open just when i press the power button and not at power off pc ( itested in both configurations)

[giulio93]

Re: Dead acer 7750g

So the problem is the super io chip or could be something else?

[giulio93]

Re: Dead acer 7750g

For PU7, see attached. It is a buck regulator that will accept a higher voltage and lower it to another required voltage. Often such regulators are based on a FB (feedback) pin which will use 2 resistors as a voltage divider to dial up the desired voltage for the output.

Review the ENable pin # 5 - what is the voltage reading there.

Expecting a logic high here to ENABLE this regulator.

If you see a logic high for the ENABLE and you also have a +5ALW rail present yet the regulator is not working, then review if the output rail is being shorted and causing an excessive current draw which will then cause this part to shut off, for safety.

For this review, remove all power, meter in resistance mode (2k scale) -> check the resistance to ground of the output coil. What is the resistance ?

If it is very low, then there may be a bad cap on this rail causing the excessive current draw. More after you post the readings.

Repeat for other rails that are not powering on.

If the ENABLE is NOT a logic high (~3v or higher), then the upstream circuit that operates the enable pin must be reviewed.



Which mosfet exactly ? Likely similar to the above - check if the enable pin is active or not. Also check the resistance to ground of the output coil (with NO power to the board).

Please don't give up with me, I'm learning

[mon2]

Re: Dead acer 7750g

Do you have both rails working on PU3 ?

+3VALWP
+5VALWP

See attached and use it to review the order of events to power on.

So with ac adapter, follow the 'A' prefixed labels (A1 -> A2 -> A3, etc.).

We need to confirm that the voltages @ A3 are present so that the EC chip is being powered -> then will accept the ON/OFF function @ A4 step -> enable signal @ step A5 will follow.

Eventually the EC must spit out some logic levels. However, note that this is a common area of failures and is a programmable device (often based on an internal 8051 microcontroller). Apparently it blows its brains out once in a while and must be reflashed with the firmware. There are special programmer tools to perform this reflashing using a flat ribbon cable and the KBC (keyboard) connector. Believe it is either SPI or JTAG interface used here.

[giulio93]

Re: Dead acer 7750g

Do you have both rails working on PU3 ?

+3VALWP
+5VALWP

See attached and use it to review the order of events to power on.

So with ac adapter, follow the 'A' prefixed labels (A1 -> A2 -> A3, etc.).

We need to confirm that the voltages @ A3 are present so that the EC chip is being powered -> then will accept the ON/OFF function @ A4 step -> enable signal @ step A5 will follow.

Eventually the EC must spit out some logic levels. However, note that this is a common area of failures and is a programmable device (often based on an internal 8051 microcontroller). Apparently it blows its brains out once in a while and must be reflashed with the firmware. There are special programmer tools to perform this reflashing using a flat ribbon cable and the KBC (keyboard) connector. Believe it is either SPI or JTAG interface used here.

But at pu2 we have already problem no? the enable signal is missing. At this pu3, according to the board diagram there is not 5VALWP rail. the 3VALWP is present instead.
What EC stay for?

[mon2]

Re: Dead acer 7750g

See attached. Perhaps I am referencing the wrong schematic from my database but PU3 = DUAL buck regulator.

This part will accept B+ from the adapter and create 2 of ALWAYS ON rails.

+3VALWP
+5VALWP

Measure the voltages on coil PL4 and also on PL5, post their values.

The +3VALWP must be working to power the EC controller chip @ U21.

Then U21 can output the enable signal of FSTCHG to enable PU2.

[giulio93]

Re: Dead acer 7750g

See attached. Perhaps I am referencing the wrong schematic from my database but PU3 = DUAL buck regulator.

This part will accept B+ from the adapter and create 2 of ALWAYS ON rails.

+3VALWP
+5VALWP

Measure the voltages on coil PL4 and also on PL5, post their values.

The +3VALWP must be working to power the EC controller chip @ U21.

Then U21 can output the enable signal of FSTCHG to enable PU2.

At pl4 and pl5 I have the 3.3V and the 5V. I had already checked the 3.3V on the U21 and it comes (so I supposed the super io is alimented).What should I check now?

[Techtiger]

Re: Dead acer 7750g

what is the voltage on PU3 pin 23 PGOOD ? EC /SIO/ Super IO (IC with same name)

[giulio93]

Re: Dead acer 7750g

what is the voltage on PU3 pin 23 PGOOD ? EC /SIO/ Super IO (IC with same name)

On pin 23 of the PU3 I have 4,96V. The name I have for this pin according to my board view is SPOK.
So the super io is the U21, it is correct?

[Techtiger]

Re: Dead acer 7750g

On pin 23 of the PU3 I have 4,96V. The name I have for this pin according to my board view is SPOK.
So the super io is the U21, it is correct?

can you confirm PU3 is your 3/5V buck controler , or upload schematic 4.96V is higher than i expect but depend on the platform

[giulio93]

Re: Dead acer 7750g

can you confirm PU3 is your 3/5V buck controler , or upload schematic 4.96V is higher than i expect but depend on the platform

I think yes. At the 24pin I have the 5.00V