Asus GL702ZC rev 2.1 no 3VALW

[Rush volkov]

Hello guys,

Well, I've acquired a broken laptop that I'm determined to fix it. I have experience repairing laptops, but I've never worked on one like this (ASUS Gl702ZC) which has a BGA-type KBC (EC/Super I/O) without pins.

I've been inspecting the motherboard and found a current draw of 0.035 A with 5V present, but theres no 3V regulated by the TPS51285A (I'll attach the datasheet).

I have the 3V and 5V Vregs, and I also have the EN corresponding to 5VA, but I dont have the PWM EN for 3VA.

(Curiously, the battery charging coil shows 19V.)

Following the schematic and power-up sequence, it seems the EN signal for 3VA comes from the EC (IT8995VG). I've scratched the PCB copper paths near the EC to ensure the signal isn't interrupted between the EC and the TPS51285A. I checked continuity with a multimeter, but the signal is simply dont coming out from the EC.

When I remove the CPU from the AM4 socket, I get some voltage on the 3V and 5V coils, though it's low and incorrect (not sure if this is normal).

So, at this point, I'm wondering if this could possibly be caused by a corrupted BIOS? or if the EC is fried and needs replacement? If replacement is necessary, do you know if it needs to match exactly in terms of numbers and letters? Or is IT8995VG-128 DXO sufficient? I can't find an identical one on Aliexpress :/ Lastly... do you think it's possible to program the BIOS through the keyboard connector using a TL431?

[Rush volkov]

Here is the datasheets and some pics

[SMDFlea]

Link to schematic - https://www.badcaps.net/forum/troubl...02zc-schematic

Reminder: rules and organization of this section https://www.badcaps.net/forum/troubl...f-this-section

[reformatt]

I'm thinking you are referring to 3VSUS_ON. It should normally be pulled high to +3VA_EC via R3053. Assuming +3VA_EC is present, I'd be checking EC pre-requisites (like power, reset etc) and then eliminating anything else on this line pulling it down first.

Look closely for corrosion at these points, it can often be as simple as that. Corrosion often does some strange things on Asus boards.

[Rush volkov]

QUOTE=reformatt;n3291890]
Look closely for corrosion at these points, it can often be as simple as that. Corrosion often does some strange things on Asus boards.
[/QUOTE]

Thanx for respond.

Yes, the schematic shows that line as 3VSUS_ON.

Thats right, the +3VA_EC is present and 5VSUS_ON/5VSUS is present too, but 3VSUS/3VSUS_ON is not present.

The paths I peled (or scratched) near of the EC and measured the path in ohms from start to finish and its ok (the multimeter shows 0.1 ohm).

I have been loonking for corrosion but it looks ok (at least on the surface). So, the next step is try to reball the EC?

[Rush volkov]

The EC Pic

[reformatt]

The schematic is somewhat ambiguous on the timing of the 3VSUS_ON signal. Seems like 3 different people worked on this drawing and all had different naming conventions. Just confirm that you don't see this line go high when you press the power button? What is the state of PM_RSMRST#?

[Rush volkov]

The schematic is somewhat ambiguous on the timing of the 3VSUS_ON signal. Seems like 3 different people worked on this drawing and all had different naming conventions. Just confirm that you don't see this line go high when you press the power button? What is the state of PM_RSMRST#?

Sorry for not respond, I was busy these days

I've been checking the motherboard and.. Yes, the 3V_SUS_ON goes high when I press the power button.

So, I decided to install the CPU, RAM and keyboard. Then I adjusted the power supply to 19.5V and 3A, when I turned on the power supply I saw the amps goes up and down, and the mosfet PQH8602 burned out.

Originally when I found this motherbord didnt have this mosfet, and I put in its place the AON7410 but I think that was not a good idea. I think i should put the PEA16BA (the original in this motherboard).

:/ now my stick RAM is dead and I feels really bad for that.

Ah... I'll be posting the newest when I get those PEA16BA from China

I really really appreciate your help. Do you know where I can find a good power on sequence schematic?

thnx 4all

Edit: its normal to find 16V in the battery charge coil in s5 state?

[reformatt]

So the board has been worked on previously? Review all other rework on the board first and double check what has been done. You are looking for components that have been replaced, checking value against the schematic and placement as well.

If you have a shorted high side MOSFET in a buck converter, it's standard practice to replace both high/low side MOSFET's and the driver IC (RT8248AGQW). While you are troubleshooting this section of the board, there should be a soldered jumper link PJP8604 that you can remove to isolate the output of the converter to the rest of the board.

AON7410 is underrated compared to the original, better to use AON7502.

As far as the schematic goes, we are lucky to have what we have. Asus schematics are very rarely available, and often full of errors (as this one is).