not understanding the measurings I made on the K55VM board

[Carlsbat]

Maybe someone can help as I'm not understanding the measurings I made on the K55VM board as follows:
the problem was that this Asus laptop was working on batteries and not charging. I took the board out and when measuring it seamed to exist a short to gnd in all regulator mosfets (drain to gnd and source to gnd) this can't be right as the computer was working...
I found that the A5 mos at supply input was in short circuit, I removed it from the board but I didn't put another one yet as I'm puzzled with this short circuit measure still found on the board.
Any ideas? What may be misleading me?

[DanielDacko]

Re: not understanding the measurings I made on the K55VM board

Inject 1V here and see what heats up, probably some ceramic capacitor. Is the adapter going in protection mode when plugged in?

[Carlsbat]

Re: not understanding the measurings I made on the K55VM board

Thanks for the reply, I suspect it could be something like that, I tried connecting a AA battery and the circuit draws 0,8A, couldn't find anything warming, there are so many caps connected in parallel it's hard to find the culprit, it could be a protection diode maybe... Must try with a power supply when I return to work bench, I was looking at the board at home with limited resources.
Anyway what I find strange is that the board was working fine from batteries, so the problem must be very close to the adapter input supply that isn't seen when in battery supply. Measuring from supply to gnd I find 1,3 ohm.

[mon2]

Re: not understanding the measurings I made on the K55VM board

Is this board still able to work from the battery only ?

What is the voltage on your battery at this time ?

If unable to work from the battery -> just remove it till the logic board is functional with the external power adapter.

Trace the external power adapter and you should find 2 x mosfets that are probably linked to a battery charger IC from TI. Post clear pictures for a review and also the markings on the topside of the charger IC.

Often, as per the detailed sticky thread above from @Piernov, the first 2 DC-in mosfets are the suspects.

With the meter in lowest scale (for starters) -> check the resistance across the mosfet pins (NO POWER when you check resistance mode):

source (1-2-3) & drain (5-6-7-8)
source (1-2-3) & gate (4)
gate (4) & drain (5-6-7-8)

Post the measurements. If you read '1' or 'OL' (over limit) on your meter -> switch to the next higher scale. Also post the scale on your meter used for the reading.

We are checking for shorted mosfets here.

If you have a donor board -> just replace the first 2 mosfets and test again.

Next, with power ON -> check the voltage on each of the pins of each mosfet.

Source (1-2-3) (the 3 pins are always ganged and shorted together)
Gate (4) - will inform us on the voltage to ON / OFF this mosfet from the charger IC
Drain (5-6-7-8)

Post the voltage of each DC-in mosfet.