ASUS GL553V Repair

[negativ3]

Hi EEV'ers,

I am kind of stumbling about trying to fault find an Asus laptop that won't start. It doesn't even show a battery charging led when the charger is plugged in, which it should. For me, a circuit diagram would be of great assistance as reverse engineering takes me a lot of time.

I have a feeling that a bypass cap has gone bad, but so many caps are reading short that I don't just want to randomly start de-soldering them with my fingers crossed.

See attached pictures of what I've probed and observed so far, any assistance you can offer to guide me on things to check would be appreciated.

[Rasz]

I have a feeling that a bypass cap has gone bad, but so many caps are reading short that I don't just want to randomly start de-soldering them with my fingers crossed

from my experience blown mosfets are more likely, unless you can see actual mechanical/water damage on the caps
removing mosfets is 30 seconds with hot air, just pul them all off and recheck

[PKTKS]

 
MLCCs are also very common pigs... they crack adhoc.

Alternative method is try using your bench supply to avoid
triggering the OCP and a thermal camera to spot the bastard...

Neither one of these two tools are cheap nor expensive.
But for this new age of microscopic tiny little things... required help

Paul

[negativ3]

I have a feeling that a bypass cap has gone bad, but so many caps are reading short that I don't just want to randomly start de-soldering them with my fingers crossed

from my experience blown mosfets are more likely, unless you can see actual mechanical/water damage on the caps
removing mosfets is 30 seconds with hot air, just pul them all off and recheck

Ok, removed and tested the three mosfets pictured as follows:

DVM on diode check
-ve to source
+ve to Drain
reading approx 0.4V

-ve still on source
+ve to gate
+ve moved over to Drain
reading 0.000V

-ve still on source
+ve still on drain
touched gate-source with a finger
reading back to 0.4V

Does this look normal? seems like they are switching ok.

A short is still present across a ton of MLCC and electrolytic caps.

[negativ3]

MLCCs are also very common pigs... they crack adhoc.

Alternative method is try using your bench supply to avoid
triggering the OCP and a thermal camera to spot the bastard...

Neither one of these two tools are cheap nor expensive.
But for this new age of microscopic tiny little things... required help

Paul

Do I set the PSU to the required voltage, turn down the current, then connect?
Seems logical but should I expect the voltage to be limited below a "certain" current?
Asking before hooking it all up...

[PKTKS]

That depends. Kinda use a common sense here.

Your goal is to spot a dead short culprit.
Some folks already have skills to do so even with alcohol
But a thermal camera is far more easy, you do see the spot.

You should guess or start by the utmost front end feeding
enough ("enough" is relative) current to have a hot spot
(considering how "hot" should hot to be visible.)

Figures like 2 or 3 Amps (using CC adjust) are enough
some hard chips require 4A or 5A (voltage will float of course
start low... up to desired)

The image of the hot spot will give you at least a region to start
Some folks even "isolate" parts of the front end to apply more
brute force to to a really hot spot.. mileage vary

Paul