Acer S7 no power

[Kashi1712]

Hi all,

I received a laptop to repair, Acer S7. I opened that one, and checked all components, everything looks ok. When I plug the power, I can hear a small tic tic tic. First, I thought it was the 2 fdmc 6679az midgets, I changed them and still the same... I can see that from the power adapter I should get 19v but when motherboard is powered, voltage goes to range 0.7 to 2.2v.

Was not able to find the schematic and boardview...

Here is a picture of the motherboard, any help would be greatly appreciated ! The Ssd on this laptop fits only for this laptop... Cannot get the data back..

Thanks a lot!

[piernov]

Re: Acer S7 no power

Sounds like a short to ground on B+ (called DCBATOUT here) line or power connector (called AD+ here).
Check resistance between the two pins of the connector. Check the resistance between the DCBATOUT line, for example on the source of the 6679AZ MOSFETs and ground.
Refer to the charging circuit schematics on page 40.

Attached is schematic for Wistron Storm found in Acer S7-391, maybe similar enough with Wistron Helium.

[Kashi1712]

Re: Acer S7 no power

So, I should check pr4004 then? Is there any value written somewhere so that I can check that one?

[Kashi1712]

Re: Acer S7 no power

So I checked pr4004, it is written r010 on it, when charging value is changing but doesn't correspond to it's value...

When not charging, value is 1.3ohm, looks like it should be less than this, right?

[piernov]

Re: Acer S7 no power

No, you should put one probe of your multimeter on ground (a screw hole, for example), and the other probe on the DCBATOUT line. You can put that other probe on PR4004, yes.

The resistance across PR4004 itself does not really matter. Except if it was burn but that rarely happens. In your case it is not. You are measuring a higher resistance because your multimeter is not made to measure such a low resistance. Conventional multimeter and probes cannot measure accurately resistance below one ohm. That is not an issue.

Also, when measuring resistance, you must disconnect all power from the board. Both power supply and battery should not be connected.

[Kashi1712]

Re: Acer S7 no power

Ok, will do that, what value shouldn't I get then?

[Kashi1712]

Re: Acer S7 no power

Took the ground from the USB port gnd.

From pu4002, first pin, 1.2ohm
From pr4004, 1.2ohm

If I test from pu3802, pin 1, I get 200kohm

[piernov]

Re: Acer S7 no power

Ok, 1.2 ohm is way too low, should be in the kiloohm or megaohm range. So yes you have a short to ground on DCBATOUT line. Now you have to figure out what is shorted.
There are many components on that line so the easiest is to hook a lab power supply set to 1V.
If you don't have a lab power supply, or any other decent power supply, you can use one alkaline battery instead.
If the CPU or the PCH get hot, stop there, you don't want to burn them if they aren't already.
If they do not get hot, you can increase the voltage (or put a two alkaline batteries in series).
Then try to find a component which gets hot.

[Kashi1712]

Re: Acer S7 no power

Unfortunately, I don't have a lab power supply, there is that noise when plugging the AC adapter, do you think it can help to identify the prob? Looks like a capacitor or a diode for me.

Probably, that I can do a check on : d3801 pc3801 pc3802, what do you think?

[piernov]

Re: Acer S7 no power

I don't think the noise would help.
It could be anything, a diode, a capacitor, a transistor, an IC… Almost everything which is connected between DCBATOUT and ground (except a resistor).
D3801, PC3801 and PC3802 are connected to AD_JK, not DCBATOUT. From your measurements, we deduced that the short is on DCBATOUT, not AD_JK.
The issue is that there are too many components on DCBATOUT to remove them one by one in order to find which one is shorted.
The best solution is to hook a power supply (or a battery) on DCBATOUT and find which component gets hot.

[Kashi1712]

Re: Acer S7 no power

Can I use isopropyl alcohol to check which one is getting hot?

[piernov]

Re: Acer S7 no power

Yes but those components can be anywhere on the board so you should try to find roughly the location where it gets hot.

[Kashi1712]

Re: Acer S7 no power

I will do it like this then, thanks ! 3.3v is it fine or can it hurt some components?

[piernov]

Re: Acer S7 no power

That is probably not your case, but a high-side MOSFET to CPU or PCH could be shorted. Injecting 3.3V would go directly to the CPU or PCH and kill them. If this was the case, the resistance between DCBATOUT and ground would be of a few ohms.
In your case 3.3V is fine I think.

[Kashi1712]

Re: Acer S7 no power

Ok, some news, 3 battery, 4.8v gives that pu3802 is hot as hell, rest looks fine, pu4001 is not hot

[piernov]

Re: Acer S7 no power

Did you connect the batteries on DCBATOUT line? It seems like you connected them to the DC jack, that would explain why PU3802 gets hot (too much current flowing through it).

[Kashi1712]

Re: Acer S7 no power

I did test from the pr4004, 3.3v, nothing gets hot, only my battery and cable gets really hot....

But, looks like that u6202 is a little bit higher in temps then other components

[piernov]

Re: Acer S7 no power

According to the schematics, U6202 is ESD protection for USB3 data lines so I don't think it can be the problem.
I don't really know what is going on…

[Kashi1712]

Re: Acer S7 no power

Yes, it is quite strange, motherboard looks really good, no burnt chip...

Only that clicking noise coming from the pu3802 is strange following me...

[Kashi1712]

Re: Acer S7 no power

I don't know if laptop is working with the battery because that one is completely discharged, if I could charge the battery, then I can check if it is working