820-00281 no power. Liquid damage.

[BCN_Techs]

Hi,

Got 820-00281 with liquid damage on UA900 area.


Replaced:

UA900
CA902
CA903
CA901
CA900
CA905
RA900

They were fucked.


Now getting 20V from the port but the machine doesnt start.


Measurements:

PPBUS_G3H 0V (shorted to ground. Injecting 5V nothing warming)
PP5V_S5 0.33V
PP3V3_S5 0.4V going down.
PP3V3_G3H 3.3V
PP3V0_G3H 0.4V and going down



Any suggestion?

 

[2informaticos]

Never inject voltage before checking if NO high-side MOSFET is shorted...

Which is the exact value at PPBUS_G3H 0V, in respect with ground?
Post it in diode mode, red probe to ground.
If is very low, then check exact value on 200 ohms scale.

"PP5V_S5 0.33V
PP3V3_S5 0.4V going down."
These require PPBUS_G3H presence first.

PP3V0_G3H is generated by U7800.

 

[BCN_Techs]

Thanks. Will check it ok the morning and back with result

 

[BCN_Techs]

In Diode mode is very low: 0.002

Resistance to ground 1,2 Ohms

 

[BCN_Techs]

Never inject voltage before checking if NO high-side MOSFET is shorted...

Which is the exact value at PPBUS_G3H 0V, in respect with ground?
Post it in diode mode, red probe to ground.
If is very low, then check exact value on 200 ohms scale.

"PP5V_S5 0.33V
PP3V3_S5 0.4V going down."
These require PPBUS_G3H presence first.

PP3V0_G3H is generated by U7800.

In Diode mode is very low: 0.002

Resistance to ground 1,2 Ohms

 

[2informaticos]

Now check in 200 ohm scale if any big coil (from secondary power supplies) has the same value to ground.
If yes, confirm to get 000 between PPBUS_G3H and that coil.
It will mean corresponding high-side MOSFET is shorted.
If no such problem found, then you can inject voltage...

BTW, remember when check diode mode (or ohm scale) on PPBUS_G3H, both charger and battery must be unplugged.
If not, you will get false short indication.

 

[JohnB8812]

Yep make sure charger unplugged. Remove F7000/1, and see if your short is on pin 1 or pin 2. If pin 1, inject 5 volts and see what heats up. If pin 2, start low around 1 volt and see what heats up. In a liquid damage case, I would not be surprised if pin 2 would be shorted through the CPU/high side mosfet as 2informaticos mentioned.

 

[BCN_Techs]

Now check in 200 ohm scale if any big coil (from secondary power supplies) has the same value to ground.
If yes, confirm to get 000 between PPBUS_G3H and that coil.
It will mean corresponding high-side MOSFET is shorted.
If no such problem found, then you can inject voltage...

BTW, remember when check diode mode (or ohm scale) on PPBUS_G3H, both charger and battery must be unplugged.
If not, you will get false short indication.

Thanks 2informaticos.


Got 2.5 Ohms on LA640, L7231, 3.5Ohms on L7221/11 and 6 Ohms on L7420/10. Seems no coil is shorted.

P:S. yep, all unpluged.

 

[BCN_Techs]

Yep make sure charger unplugged. Remove F7000/1, and see if your short is on pin 1 or pin 2. If pin 1, inject 5 volts and see what heats up. If pin 2, start low around 1 volt and see what heats up. In a liquid damage case, I would not be surprised if pin 2 would be shorted through the CPU/high side mosfet as 2informaticos mentioned.

Shorted on pin 2 , PPBUS_G3H.


The liquid damaged very small area, UA900 and few componentes near it.

 

[BCN_Techs]

injecting through pin 2 seems be GPU. Getting warm and producing electric sound. Dead?

 

[2informaticos]

If the reading on PPBUS_G3H is lower than any coil, then is no shorted high-side MOSFET.
Should be a capacitor, or some IC directly connected to the main power rail.
However is no reason for GPU to overheat when inject, if high-side MOSFET of its power supply is not shorted.
Be sure you took correct readings from all coils...

BTW, don't quote an entire post; just select the related words.

 

[JohnB8812]

If the GPU is getting warm, that's not good. Inspect closely by it for caps that may be heating. If the only thing getting warm is the GPU, this is done

 

[BCN_Techs]

I think GPU is dead. The only thing is getting warm is GPU.

 

[2informaticos]

Check resistance (200 ohm scale) between PPBUS_G3H and LA900:
Do the same for LA640/50.
And then compare with resistance to ground on all these points...

 

[BCN_Techs]

On LA900 1.645 kohms, LA640/50 2.9 to ppbus and 2.2 ohms to ground.

 

[2informaticos]

I forgot about LA300, is on GPU too.
If don't get lower value between PPBUS_G3H and any of GPU power supply, then is very strange to get hot GPU...