Hp15 quanta u83 io thermal protection

[mcplslg123]

M/B CODE-HP 15 DAOU83MB6EO REV E

PROBLEM: When trying to switch on the laptop, power light blinks,fan moves abit, no display.

Observation: Problem seems to be that of "IO THERMAL PROTECTION" as can be seen at page 4 of schematics. I'm getting 3.3v at one side of R78/76. There should be 3.3v on the other side as well(I think so) but i'm getting 0.8v on the other side of resistance. R504 is not populated on the m/b and I'm getting 3.3v on one side of R509 as well but 1.2v on the other side of R509. All this is diretcly connected to ene kbc.

I have checked resistance R76/78/509 and all seems fine as per schematics.

I just jumpered R78 to get 3.3v on the other side of resistance and got 3.3v, It worked,got display but again same problem after 24 hours.

Can anyone of you please explain this circuit or a way out. Or do i need to replace the ene kbc??

Please suggest.

[mcplslg123]

Re: Hp15 quanta u83 io thermal protection

No advice friends???

[piernov]

Re: Hp15 quanta u83 io thermal protection

The thermal protection is triggered if either:
— Voltage on THRM_MOINTOR is lower than 1.8V
— Voltage on THRM_MOINTOR1 is lower than 1.2V
If they are higher (by a substantial margin) then it is not the source of your problem.

The circuit is a voltage divider which will set the voltage for both THRM_MOINTOR and THRM_MOINTOR1.
The temperature is reported by R504: its resistance will decrease when the temperature increase.

Let's do some computation:
If R504 resistance is 19kohms at 65°C, voltage on THRM_MOINTOR is 3.3V * (R504+R76)/(R504+R76+R78) = 1.9V, close enough.

If R504 resistance is 13kohms at 75°C, voltage on THRM_MOINTOR1 is 3.3V * (R504)/(R504+R76+R78) = 1.3V, close enough.

(notice that R76 is either at the top or bottom of the voltage divider depending on whether you measure THRM_MOINTOR or THRM_MOINTOR1)

At ambient temperature (let's say this area is at 30°C right after you start the machine so R504 is 80kohms):
THRM_MOINTOR =2.75V
THRM_MOINTOR1 = 2.65V


However, you say that R504 is not populated on the motherboard, which doesn't make sense because this is the key for this circuit to work (it's a thermistor, sensing the temperature) and it's not marked as no stuff in the schematics. Take a closer look at the pads to check if it was ripped off the board.
Also, if R504 is not present, you should get 3.3V on both THRM_MOINTOR and THRM_MOINTOR1, since it will not act as a voltage divider anymore (no path to ground).

[kiraro]

Re: Hp15 quanta u83 io thermal protection

Thank you for your explanation piernov .

[mcplslg123]

Re: Hp15 quanta u83 io thermal protection

Sorry, its R509 which is not populated.

[mcplslg123]

Re: Hp15 quanta u83 io thermal protection

As i told earlier, If i jumper R78 i get 3v at both ends and mobo starts working. But why then it doesnt switches(Swithches and instant off-no display) next day?? Thanks for the explanation piernov.

[piernov]

Re: Hp15 quanta u83 io thermal protection

R509 should be populated too.

Remove the jumper and check the voltage on THRM_MOINTOR and THRM_MOINTOR1.
Check also the resistance to ground on THRM_MOINTOR and THRM_MOINTOR1.

[mcplslg123]

Re: Hp15 quanta u83 io thermal protection

R509 should be populated too.

Remove the jumper and check the voltage on THRM_MOINTOR and THRM_MOINTOR1.
Check also the resistance to ground on THRM_MOINTOR and THRM_MOINTOR1.

R509 not populated-100% sure as checked with another mb.
THRM_MNT-0.76V
THRM_MNT1-0.0V
(After removing jumper on R78)

[piernov]

Re: Hp15 quanta u83 io thermal protection

Ok, R509 being not populated is strange: R504 is therefore useless and this circuit doesn't do anything…

Anyway, what about resistance to ground of both lines?
It sounds like THRM_MNT1 is shorted to ground.

[mcplslg123]

Re: Hp15 quanta u83 io thermal protection

Resistance to ground is all ok. Only R504 one end is gnd which is normal.

Anyway, i have removed the jumper on R78(16.5K) and replaced it with 0 Ohm resistance. Its working fine now. I'm getting 3.3v at both ends of R78 and 1.36v at R76. So well above the io protection values.

Though i was able to resolve the issue but still puzzled why not getting 3.3V at R78 when there is no ground and ratings are all ok, no corrosion as well.

Thanks piernov for your explanations and support.

[piernov]

Re: Hp15 quanta u83 io thermal protection

If there is nothing inbetween THRM_MOINTOR1 and ground its voltage should be 3.3V too, so it sounds like something is wrong on this line.
So you may have a bad connection (bad solder joint, bad trace), a bad capacitor (C135 for example) or a bad EC.
I hope that this fix lasts.

[mcplslg123]

Re: Hp15 quanta u83 io thermal protection

Bad solder joint or trace is ruled out as i have checked under magnifier. I too doubt bad EC as i said in the first post. Its working since the last 48 hrs so hopefully it will work. If it troubles anymore, will replace EC. Thanks for your time mate.