Asus X555LD, Won't power back on after being shut down.

[gcain]

First post here, if there is another forum that's better suited, let me know please.

I have an Asus X555LD board come in with a blown backlight and no image.

Managed to repair those two issues, but now the board will only turn on once when the power is connected. When I power it off, the adapter and battery need to be disconnected and reconnected before it will power back up again.

Aside from that it seems to run okay.

Any suggestions on where to start measuring?

[mcplslg123]

Re: Asus X555LD, Won't power back on after being shut down.

Do you have 3.3v on power switch?? If you do have then check RTC section. If you have schematic post it here.

[gcain]

Re: Asus X555LD, Won't power back on after being shut down.

I've uploaded all the docs I have on this board.

Will take measurements when I get back to the office again.

[gcain]

Re: Asus X555LD, Won't power back on after being shut down.

@mcplslg123 I do have 3.3v on the power switch. It pulls low when I press it too.

[mcplslg123]

Re: Asus X555LD, Won't power back on after being shut down.

You mean backup battery or cmos battery need to be pulled?? I assume backup battery is what you mean. Have you checked Qm3024 fets(2 connected to dc in and the other one to battery output?? Gate voltage on fets at dc in?? Do you get charging indicator? I suspect something wrong with ac-dc output in charging section. have you flashed bios??

[gcain]

Re: Asus X555LD, Won't power back on after being shut down.

@mcplslg123 I don't follow.

I mean when I press the button the 3.3v goes low, as it should.

Would I really need to flash the bios?

[caspian]

Re: Asus X555LD, Won't power back on after being shut down.

Bios flashing is not recommended now until you finish some basic measurements to discover what the problem may be.

[mcplslg123]

Re: Asus X555LD, Won't power back on after being shut down.

@mcplslg123 I don't follow.

I mean when I press the button the 3.3v goes low, as it should.

Would I really need to flash the bios?

Yes, it can be 'coz of bad bios and thats why i recommended flashing bios. I dont know why caspian differed with me in opinion. Btw, you didnt replied to my query regarding fets.

[gcain]

Re: Asus X555LD, Won't power back on after being shut down.

Sorry mcplslg123, the cmos battery comment made me thing you had the wrong thread.

I can't find a faulty mosfet, they all seem to measure okay (I'm not familiar with PC though, I tend to only work on Apple Logic boards).

One thing I have noticed, the IT8585E IC (KBC I think) get's so hot almost instantly that I can't put my finger on it when the machine is running.

If you can direct me on what you need measure it would be helpful, I haven't had the ahhh-haaa moment with these yet and am wondering a little blind.



Edit: compare the IT8585E temperature with another board, and the known good board runs cold.

[mcplslg123]

Re: Asus X555LD, Won't power back on after being shut down.

Oops that smells like a bad kbc. Resistance to ground on PIn26 or pin50 of kbc?? I feel you need to replace kbc.

[caspian]

Re: Asus X555LD, Won't power back on after being shut down.

Dear mcplslg123,
I always respect your recommendations. you helped me in a number of my laptop repairs. This is a great forum where experienced technicians cooperate in repairing laptops. This cooperation is really helpful.

Dear gcain,
Does any other component get hot too?

[mcplslg123]

Re: Asus X555LD, Won't power back on after being shut down.

Dear caspian, I dont mind. Everyone's analysis or understanding will differ in some sense and thats good for a final solution as we can rule out the odd ones. Your contribution in the forum is great. Keep up the good work bro.

[gcain]

Re: Asus X555LD, Won't power back on after being shut down.

Oops that smells like a bad kbc. Resistance to ground on PIn26 or pin50 of kbc?? I feel you need to replace kbc.

26 = ~2MOhm or 0.416v in diode mode.
50 = same as above.

Those figures seem about right to me.

Does any other component get hot too?

Not that I can feel.


I have the identical chip from another board, does it need to be flashed?

[mcplslg123]

Re: Asus X555LD, Won't power back on after being shut down.

IT8585E is programmable but it will automatically be flashed once you turn the mb on with new kbc. Do remember to put up screen while turning on after installing new kbc so that you can see if any message pops up during kbc flash. Since you have a spare kbc , i'll suggest to change it.

[gcain]

Re: Asus X555LD, Won't power back on after being shut down.

I swapped out the IT8585 for another and everything is working again.

Well, except for the trackpad, but I think that's another issue.

Thanks everyone for the advice and help.

[mcplslg123]

Re: Asus X555LD, Won't power back on after being shut down.

Happy to know you fixed it.

[t.danes]

Re: Asus X555LD, Won't power back on after being shut down.

Can anyone advise me on what I should focus on when the voltage fluctuates around 2.9v on the bios chip, there is instead of 3.3v, I also changed the bios chip and it is still the same without the bios chip there is 3.3v. I couldn't find the schematic anywhere

[mon2]

Re: Asus X555LD, Won't power back on after being shut down.

Remove all power -> meter in resistance mode -> check the resistance to ground of the bios pin (Vcc).

If the voltage is dropping AFTER the bios is placed then there is a fault with the BIOS chip. Are you replacing with 100% same component? Check the solder connections. Some fault is causing this voltage rail to be lower.

With the bios installed, is the logic board working properly?

What is the part number of the original bios chip ?

What is the part number of the bios chip that is causing this voltage rail to be lower?