Understanding Laptop Discharge Circuit

[ocf]

Hello Guys and Gals,

I have a waterdmaged HP Laptop motherboard, it switches on and off repeatedly every 5 seconds, the liquid damage is very localised, the circuit diagram below is of the affected area

The Schematic labels this as discharge IC there are also two other circuits on the same page but these are untouched by the water damage and dont seem to be directly linked to this one.

I have circled a couple of parts of the circuit that are not present on my motherboard.

https://postimg.org/image/bnkcws6x1

I have tested PR52,55, 56 and 57, they are showing incorrect values and I think will need to be replaced, I have the SMD resistors on order.

I am trying to get a better understanding of how the circuit functions to help aid in testing.

MPHY_PWREN looks to be the start of it all, this jumps from 0v to 3.3v as the laptop switches on and off.

The +VIN is 19v, once it passes through the PR52 1m resistor what should the voltage be?

I see 19v coming in to PR52 and 0 out, showing open with a multimeter definitley needs replacing

Does the MPHY_PWREN signal entering pin 2 of PQ6 complete the ground for the +VIN rail to flow?

Is the 1.05VMOD_ONG the +VIN after it has been reduced by PR52?

Any help would be greatly appreciated

I have a feeling I am going to read this post back in an hour and realise I could have structred it better. Please ask me to explain anything in more detail!

[budm]

Re: Understanding Laptop Discharge Circuit

MOSFET PQ6 (used as a switch) Source and Drain pins are connected in parallel with PR55 1M4 resistor, PR52, PR55 form Voltage divider so when PQ6 is not turned on (0Vdc at the GATE), the the Vdrops on PR55 will = 1/2 of +VIN because PR52, PR55 are the same value.
When PQ6 is turned on (3.3Vdc at the GATE) then the Voltage on PR55 will be 0V.
They use very high value resistors in the at section of the circuit so any contamination will have affect in the circuit.
PQ9, PQ5 are also used as a switched all driven by PQ6. PQ5 controls PQ10.
When PQ6 is ON, PQ5 is OFF, PQ9 is OFF, PQ10 is ON and provides 1.05V at the output side of inductor PL1.

The question is why the control signal MPHY_PWREN that drives PQ6 is going on and off: 'MPHY_PWREN looks to be the start of it all, this jumps from 0v to 3.3v as the laptop switches on and off.'

[ocf]

Re: Understanding Laptop Discharge Circuit

The control signal links back to one of the controller IC's I think its a bga package, I will see if I can find a test point.

I hope the short didn't fry it!

[ocf]

Re: Understanding Laptop Discharge Circuit

MPHY_PWREN goes to point Y2 on IC U25, definitley a BGA package judging from the number of pins, the only chip I can see thats big enough is the Processor which is integrated on tot he board.

In the mean time I checked the 3.3 and 5v regulators, both stable

Can you advise what the MPHY_PWREN is doing in the circuit, I'm still having difficulty understanding the circuit overall, it controls the charging/discharging of the battery, so it sees when the DC charger is connected senses the +VIN and starts powering the system from battery.

I dont see any reference to battery connector or voltages that would charge a battery, only the VIN and 1.05v out.

Below is an image of the remaining circuit diagrams from the same page of the schematic

https://postimg.org/image/u6qi89htx/

What are these in relation to the previous one I posted?

[ocf]

Re: Understanding Laptop Discharge Circuit

U25 is the processor, cant find a test point for Y2.

Should I continue testing if I have gotten this far and a signal coming out of the main chip is bad? I cant find the line feeding the chip voltage, I guess this would be the CPU VCORE rail.

[ocf]

Re: Understanding Laptop Discharge Circuit

Image below shows the U25 chip that the MPHY signal seems to originate from, on the right hand side I have highlighted another reference to the same signal, it shares a rail with a load of other lines that all seem to be powered by 3v.

I have tested another component on this rail and it is also going between 0 and 3v,
If I saw my 3.3v DC regulator outputting a stable 3v what is causing the instability.

Is this 3v rail different from the 3v output by the DC circuitry

https://postimg.org/image/8nf1823p1/

[ocf]

Re: Understanding Laptop Discharge Circuit

Any more input BudM or did I go and confuse you aswell as myself :P