Cpu_core signal missing. Lenovo g50. Help?

**Weelcup** · 07-31-2018, 06:58 AM

Re: Cpu_core signal missing. Lenovo g50. Help?

Originally posted by bluestone

Check Ec pin 99 and pin 30

Pin99=3.3V
Pin30=0V

**caspian** · 07-31-2018, 09:34 AM

Re: Cpu_core signal missing. Lenovo g50. Help?

Now, discovering the faulty component requires more thinking and analysis of the mainboard, because the mainboard is complicated and any unexpected fault may be there. Do not replace PCH or SIO in a hurry.

**Weelcup** · 07-31-2018, 12:11 PM

Re: Cpu_core signal missing. Lenovo g50. Help?

Originally posted by caspian

Now, discovering the faulty component requires more thinking and analysis of the mainboard, because the mainboard is complicated and any unexpected fault may be there. Do not replace PCH or SIO in a hurry.

I agree,
interestingly, I have replace Q39,Q40 Mosfets. both seemed to be fully working though. but the board powered up normally for 1 min and I was able to enter the bios and check the info. then the board turned off. and the same problem started again. I tried to replace the mosfets again but I got nothing. I am now very confused of what might connect the mosfets with the problem and why it worked. was it the heating near the cpu or the mesfets or a cut in circuit near the mosfets??? like you said Caspian "it might be anything"

**caspian** · 07-31-2018, 12:25 PM

Re: Cpu_core signal missing. Lenovo g50. Help?

If so, turn it off and measure resistance on PQ39 and PQ40 and pin1 of PU908. check whether there is any short.

**Weelcup** · 07-31-2018, 03:02 PM

Re: Cpu_core signal missing. Lenovo g50. Help?

Originally posted by caspian

If so, turn it off and measure resistance on PQ39 and PQ40 and pin1 of PU908. check whether there is any short.

I have checked it. there is no short to ground and the mosfets are ok.
between the two mosfets and the ground = 32ohm

while between mosfets and pin1 = 1.65K

**caspian** · 08-01-2018, 01:41 AM

Re: Cpu_core signal missing. Lenovo g50. Help?

Had you replaced PQ39 and PQ40 before starting this thread?
If so, you have probably damaged PU908 or the SIO.
If not so, which post have you replaced PQ39 and PQ40 at?

**Weelcup** · 08-01-2018, 07:10 AM

Re: Cpu_core signal missing. Lenovo g50. Help?

Originally posted by caspian

Had you replaced PQ39 and PQ40 before starting this thread?
If so, you have probably damaged PU908 or the SIO.
If not so, which post have you replaced PQ39 and PQ40 at?

Yes I replaced the two mosfets before starting the thread.

What I did so far are the replacements below in sequence:

Replaced UL1 as it was getting warm.
Reprogram the bios and the EC
Replaced the PQ39,PQ40
Replace PU908
Replace PQ39,PQ40 again
Replaced PC989 and PC708
Reprogrammed the Bios and the EC again.

Only when I replaced the 2 mosets at the first time I got it worked for about a 1min.

Can I know why would these mosfets damage the PU908 or Super IO. ?

**SMDFlea** · 08-01-2018, 07:52 AM

Re: Cpu_core signal missing. Lenovo g50. Help?

Is the voltage stable on 3VS, check Q24 and +20VSB .If its ok check PR617 and PC621

**Weelcup** · 08-01-2018, 10:11 AM

Re: Cpu_core signal missing. Lenovo g50. Help?

Originally posted by SMDFlea

Is the voltage stable on 3VS, check Q24 and +20VSB .If its ok check PR617 and PC621

The 3.3VS is not flactuating while checking via multimeter. But I don't have osciliscope to check the pattern. So I assume it is stable.

###########
At Q24:

Pin4 =19.8v
All other pins = 3.3v
############

PR617 have 0V.. and measures 5ohm
PC621 have 0v ... and measures 39ohm at non-grounded pin.

**Weelcup** · 08-01-2018, 10:34 AM

Re: Cpu_core signal missing. Lenovo g50. Help?

But at PU602 pin7 the multimeter flactuate between 0.696V and 0.702V does that mean it is not stable?

Also, the same happens at PU202 pin6.

**SMDFlea** · 08-01-2018, 11:15 AM

Re: Cpu_core signal missing. Lenovo g50. Help?

No,thats not fluctuating at all.

**SMDFlea** · 08-01-2018, 11:28 AM

Re: Cpu_core signal missing. Lenovo g50. Help?

Check PU908 pin 1, what voltage do you get when you press the power button

**Weelcup** · 08-01-2018, 01:18 PM

Re: Cpu_core signal missing. Lenovo g50. Help?

Originally posted by SMDFlea

Check PU908 pin 1, what voltage do you get when you press the power button

Actually whenever I connect to 20v power supply the power led gets on. And when I press the power button to turn it off it doesn't. In stead, it just restart. So I just see a one time blinking led.

But as you advised, I measured the voltage at pin1 exactly at the moment when I connect to power supply. Interestingly there is an increase in the volage at pin1 which come and gone in a matter of milliseconds. The same thing happens when the power led blinks when I press the power button for a while.

The max my multimeter reach during those milliseconds was 0.370v.

**caspian** · 08-01-2018, 02:48 PM

Re: Cpu_core signal missing. Lenovo g50. Help?

now continuously monitor voltage on PL9 to see whether it has a rise or it is absolute 0. If it has a rise for a millisecond, how much is the voltage rise?

**Weelcup** · 08-02-2018, 04:51 AM

Re: Cpu_core signal missing. Lenovo g50. Help?

Originally posted by caspian

now continuously monitor voltage on PL9 to see whether it has a rise or it is absolute 0. If it has a rise for a millisecond, how much is the voltage rise?

Doing the same procedure, No there is nothing at all on PL9.

**SMDFlea** · 08-02-2018, 05:58 AM

Re: Cpu_core signal missing. Lenovo g50. Help?

Redo PU908, do the same tests afterwards .

**caspian** · 08-02-2018, 06:18 AM

Re: Cpu_core signal missing. Lenovo g50. Help?

first, remove PR9146 and measure voltage on both sides of PR9146 and PR9343.

**SMDFlea** · 08-02-2018, 08:14 AM

Re: Cpu_core signal missing. Lenovo g50. Help?

Originally posted by caspian

first, remove PR9146 and measure voltage on both sides of PR9146 and PR9343.

Ah yes, to see if voltage is on EC_VR_ON,CPU_VR_ON or both. If the voltage is on both check PC620 next ?

**Weelcup** · 08-02-2018, 02:36 PM

Re: Cpu_core signal missing. Lenovo g50. Help?

Originally posted by caspian

first, remove PR9146 and measure voltage on both sides of PR9146 and PR9343.

I just did the measures.
PR9343 already not installed by the manufactur.but I removed PR9146.

Interestingly , there is a raise in voltage on PU908 pin1 to about 0.9V as soon as drops to zero then raise again and so on.

But there is nothing on the other side of the resistor. So the CPU_VR_ON & EC_VR_ON are both 0V...

I Shared a short video of the voltage with you on the following link:

https://drive.google.com/file/d/1w4d...w?usp=drivesdk

**caspian** · 08-02-2018, 11:06 PM

Re: Cpu_core signal missing. Lenovo g50. Help?

do not solder PR9146 back on the board until you fix the CPU_VR_ON signal. Since there is no CPU_VR_ON, it seems the PCH is faulty. that is not good. to make sure, reprogram the Bios and the EC using the original dump while PR9146 is removed.

Cpu_core signal missing. Lenovo g50. Help?

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