HP 4720s Laptop does not respond to the power button

[n3v3n]

Hello,

HP 4720s Laptop does not respond to the power button

Now, if there is any good soul to direct me to where to measure with a multimeter to see what could be a possible problem.

And another question, if the southbridge is "broken", laptop should start or that could be the cause of not powering on?



And if anybody have schematics or HP Pro Book 4720s that would be great.

regards,

n3v3n

[khaahk]

Re: HP 4720s Laptop does not respond to the power button

Do you have voltage (approx 8V) on the grey wire? (Pin 7 of the DC in connector)? If not, then you might have a faulty adapter. I believe the probook uses the HP smart adapter.

[n3v3n]

Re: HP 4720s Laptop does not respond to the power button

I will check those 8V

Problem is same on battery. It won't start.

I had issues with laptop turning off by himself even in BIOS (like his chipset is overheating).

Yes, my ProBook have smart pin on power adapter.

[n3v3n]

Re: HP 4720s Laptop does not respond to the power button

I didn't understand what you mean about PIN 7 on DC In

here is better picture

[spleenharvester]

Re: HP 4720s Laptop does not respond to the power button

Looks like burn marks/liquid damage near R429 to me, above the MOSFETs by the DC socket.

[dj_ricoh]

Re: HP 4720s Laptop does not respond to the power button

Looks like burn marks/liquid damage near R429 to me, above the MOSFETs by the DC socket.

Neeaa i saw like on 70% of them isolation tape . you know when you peal of.

[khaahk]

Re: HP 4720s Laptop does not respond to the power button

Sorry, i meant pin 6 (grey wire), connector DCI where the adapter connects.
Is the battery charged, maybe it is empty and wont't start because of that?
Does the computer show any battery charging lights when adapter and battery connected?

[n3v3n]

Re: HP 4720s Laptop does not respond to the power button

if it is grey wire, pin 6. there I get 1.3V. Battery is still around 80% full.
When I connect battery to mainboard and connect charger light doesn't show.

And no, nothing is spilled on laptop. I know because it's my laptop.

And regarding power adapter. I get 19.97V on + and -, and I get 15.8V on - and smart pin.

[khaahk]

Re: HP 4720s Laptop does not respond to the power button

That 1.3V is strange, but ok if the battery is charged and the laptop still wont react to power button.
First - how did it happen, one day the laptop just did not start or did it turn off during work?
You can try to:
1. Remove CMOS battery. Wait, and try to power on again.
2. Measure voltage on power button
3. Find U90 - RT8205, measure:
PIN 20 - VIN:
PIN 13 - EN:
PIN 8 - REG3:
PIN 17 - REG5:

Datasheet attached

[n3v3n]

Re: HP 4720s Laptop does not respond to the power button

Laptop worked till this Sunday, I was working and I had to restart laptop and then in BIOS computer turned off and on again and It go like that indefinitely. So I removed battery and reattach battery and it started and it started to turn off and on again and I have removed batter again and from that point nothing.

Regarding measure, results will be around 21h.

[dj_ricoh]

Re: HP 4720s Laptop does not respond to the power button

Laptop worked till this Sunday, I was working and I had to restart laptop and then in BIOS computer turned off and on again and It go like that indefinitely. So I removed battery and reattach battery and it started and it started to turn off and on again and I have removed batter again and from that point nothing.

Regarding measure, results will be around 21h.

did you try a reflow? maybe the chipset its going f.u.b.a.r

[n3v3n]

Re: HP 4720s Laptop does not respond to the power button

that was my question from start.

If chipset is fuc....d, can that be problem with powering on?

And, answer is no, I didn't try to reflow. Better idea is to reball chipest. I have equipment for that.

this is the link of full size picture

[dj_ricoh]

Re: HP 4720s Laptop does not respond to the power button

do to the fact its a board with video dedicated ... it will better if you do a reball.
if it works the order a new chip.
take pic of the video chipset

[n3v3n]

Re: HP 4720s Laptop does not respond to the power button

I will take pictures of whole board today when I come home.

But I'm not talking about video chip, I'm talking about chipset.

LINK

[khaahk]

Re: HP 4720s Laptop does not respond to the power button

I would'nt go reballin/reflowing before checking power first, bios second. If PCH does not work, yes then the machine can act like you described. But it can also be power or bios problem.
Sorry - why did you have to restart the computer? Because it went crazy, did you do an update or ... ?
If the machine turned off while being in bios (did you go to bios?) or did you mean before loading OS, then i would first look towards bios. The standby power 5V/3.3V is easy to check before going to reprogramming bios, so it is good to do first.

[n3v3n]

Re: HP 4720s Laptop does not respond to the power button

I had to restart because I wanted to turn off Digital drivers signing. Windows 8 is installed.

Laptop know to switch off while I was working in windows. Then I realized that one screw broke on heat sink which is "cooling" PCH. I have repaired screw and put heat sink back to place. (that was 2 months ago).

Forgot to mention, from day 1 PCH was really hot while working on laptop.

switching off and on is random, sometime while in POST (showing HP logo) and sometime while booting windows.

[n3v3n]

Re: HP 4720s Laptop does not respond to the power button

can't find U90, where is his location? I have found U91, U92 .... but can't find U90.

Anyhow, I think I have found problem. My PCH looks broken in corner.

link to full size image

[khaahk]

Re: HP 4720s Laptop does not respond to the power button

If you mean on the picture right lower corner - might be.

[spleenharvester]

Re: HP 4720s Laptop does not respond to the power button

Definitely looks like a possible cause. The top of that chip looks very rough, did something happen to it?

It's also possible it was like that from factory.

[n3v3n]

Re: HP 4720s Laptop does not respond to the power button

Chip doesn't look like this when you are just looking at chip, if you are talking photo with big zoom than you can see scratches.

I'm talking about lower left corner.

@khaahk

I couldn't find U90, I can find it on schematics you sent me bu can't find it on mainboard.