dynabook Satellite Pro c50-h-W10 power issue

[Sraros]

Hello,

I have this laptop that is not charging at all.
Removing the MB I first noticed the PET film insulator at the back is thermal shrinked seemingly coming from the battery circuit and heavily distorted behind the 2nd DC-in mosfet Q25 (MDV3604).
The battery itself is drained to 0, with one cell being a little bulgy. I guess the battery died and the circuit tried to push amperes in it?

Anyway with a 19.5V adapter (not original) hooked I have 19V on drain of the 2nd DC-in mosfet.
I have a short to ground on inductor L9, TC17, TC16 and several caps around.
The cap pointed with a red arrow almost fell off when probed as the solder probably melted from the short (still the cap out of circuit is not shorted)
A small solder ball on the drain of PQ5 (MDV3604).

Charging Controller PU1 is BQ24780S

Now, I read the sticky for laptop battery charging circuit troubleshooting, but I would appreciate if there was a point out as to how to find the short. If I am to hook up a 1V, should I input it on the drain of PQ5? (right next to it there's a pad of cathode D45)

[mon2]

Re: dynabook Satellite Pro c50-h-W10 power issue

Where you measure a low resistance to ground yet the rail should be a higher voltage than 1 volt is a candidate for voltage injection. Need to be sure to keep the voltage low at 1 volt or lower to start. Higher current is ok.

We use 0v8 at 30A for injection which nukes out the shorted part.

The key point is to ideally prevent the CPU from getting hit with a high voltage injection, in case there is a high side mosfet that is leaky.

[Sraros]

Re: dynabook Satellite Pro c50-h-W10 power issue

Thank you for the info.
As I don’t have a proper bemch power supply, would a DC-DC stepdown converter with output 1V constant and max current 4.5A be able to inject to find the short?

[mcplslg123]

Re: dynabook Satellite Pro c50-h-W10 power issue

Wrong direction. TC16/17 are part of Vcore circuit and its supposed to be high current,low resistance rail. Set your meter to ohms mode and then put black probe to GND and red probe on postive side of TC16/17. What is the exact reading?(Meter should be set to 200 Ohms). Dont inject voltage here as you may kill the cpu.

[Sraros]

Re: dynabook Satellite Pro c50-h-W10 power issue

Positive or negative started with 1 Ohm and after checking over some more, dropped to 0,6 Ohm

[Sraros]

Re: dynabook Satellite Pro c50-h-W10 power issue

I am writing again in better english, hopefully
Anywhere I measured in this rail, I had 1 Ohm resistance to ground. As some time passed the resistance measurements were dropping up to 0,6 Ohm

[mon2]

Re: dynabook Satellite Pro c50-h-W10 power issue

The battery may be defective and perhaps is now locked from being deep discharged. Respectively, test with another known good battery.

Remove the battery.

Does the laptop power up an function normally without the battery?

[Sraros]

Re: dynabook Satellite Pro c50-h-W10 power issue

Erm, all the tests were without the battery connected…

[Sraros]

Re: dynabook Satellite Pro c50-h-W10 power issue

Not to underestimate any of you but as I am left with split advice, I am a little in doubt here.
Is it safe afterall to inject a 1V power into that rail?
Are these readings I posted enough to say there’s a short to ground or is it normal?

[Sraros]

I want to give another shot on this laptop.

Here are some more information:
TC1, TC11, TC14, TC13, TC16, TC17 are all shorted rails. 0Ω) i lifted them 1 by 1 and they all test fine out of circuit.

Then removed some components like in photo attached but still have the same result.
After L9 removal at least the short to ground disappears on the left pin.

[Sraros]

Some additional information that may help
L9 is the 5V rail
L8 the 3.3 rail
PL1 the battery charging rail, 8V
on PQ5 I have 19V coming from the right side

[Sraros]

Finally found the short at U22 QFN reading ALTM689.
I ordered the part as NB679 as I found it from another post here. So waiting for it and hopefully it comes back to life…