HP 250 G8 EC cannot reach BIOS

[someonenotyou]

Hi.

I got HP 250 G8 which has blinking Caps Lock - 5 long, 3 short - This condition indicates the embedded controller cannot reach the BIOS within the established time limit.
When I got the laptop, it did not turn on at all. The power button was dirty. After cleaning the button it stops at blinging Caps Lock.

When I power on the board, I get a fan spin at the start, then it stops. Then the CPU and inductors get really hot. The fan does not turn on for cooling.

Then I notices that MOSFETs have a solder balls on the pins, like they got really hot as well (but I couldn`t feel by hand).


Could it be a bad CPU drawing too much current?
Where do I start to look?

Thank you.

[mcplslg123]

Never try to turn on a 10the gen onwards intel cpu without heatsink as it draws a lot of current during initial boot up for almost a minute or so.

Heasting is normal for such cpu.

[pc_okay]

Hello,

Do you try replacing ram if removable?
You where talking first about bios issue, you should try recover bios with HP procédure. (Sometimes it works…

https://support.hp.com/ca-fr/documen...881-4029009-16

[someonenotyou]

Never try to turn on a 10the gen onwards intel cpu without heatsink as it draws a lot of current during initial boot up for almost a minute or so.

Heasting is normal for such cpu.

I did not tur it on without heatsink. I just removed it to see if there was any burnt component under the heat pipe.
I noticed the CPU got hot because the heat pipe got really hot and the fan did not turn on to cool it.

[someonenotyou]

Hello,

Do you try replacing ram if removable?
You where talking first about bios issue, you should try recover bios with HP procédure. (Sometimes it works…

https://support.hp.com/ca-fr/documen...881-4029009-16

I already tried to recover BIOS using USB flash. Tried many times, leaving for 5+ minutes (don`t want to leave longer as the CPU gets very hot). The screen stays dark and no activity on USB.
Tried with Win+B, Win+V, B, V key combos.

[SMDFlea]

Look for loose ram slot pins

[someonenotyou]

Look for loose ram slot pins

Checked all of them, they are solid on the board. And no debris between the pins, so no short.

How can I check if the EC is not defective?

[pc_okay]

Do you have schematic or bv ?

[someonenotyou]

Do you have schematic or bv ?

Yes, I just uploaded them here - HP 250 G8 FPI50 LA-H329P Schematic and Boardview - Badcaps

[pc_okay]

Check sys_pwrok and plt_rst signals.
If présents (3v approx) you can try reprogram bios manualy.

if bios reprogrammation doesn’t help Check DRAMRST signal.

Then Report your result here.

[mcplslg123]

Newer HP's soldering is pathetic. The soldering seems perfect even under microscope but still they are problematic.

Had a hp X360 with ryzen 5 cpu and nvme ssd was intermittently detecting. The ssd slot seemed perfect but just resoldered the slot and now it works perfect.

May be just resoldering the ram slot may help.

[someonenotyou]

Check sys_pwrok and plt_rst signals.
If présents (3v approx) you can try reprogram bios manualy.

if bios reprogrammation doesn’t help Check DRAMRST signal.

Then Report your result here.

SYS_PWROK - 3.3v
PLT_RST - 0.009V

DRAMRST - 0.010V

[someonenotyou]

Newer HP's soldering is pathetic. The soldering seems perfect even under microscope but still they are problematic.

Had a hp X360 with ryzen 5 cpu and nvme ssd was intermittently detecting. The ssd slot seemed perfect but just resoldered the slot and now it works perfect.

May be just resoldering the ram slot may help.

I checked all the PINs with tweezers trying to move them.

[pc_okay]

Ok regarding your first post about bios issue and PLT_RST missing, it defintly could be a bios issue.
HP bios recovery doesn’t work every Time.

I suggest you (if you Know how to reprogramm it) to post your bios in bios section and ask for a clean BIOS.

You can Also Check résistance to ground on plt_rst Line too.

[someonenotyou]

Ok regarding your first post about bios issue and PLT_RST missing, it defintly could be a bios issue.
HP bios recovery doesn't work every Time.

I suggest you (if you Know how to reprogramm it) to post your bios in bios section and ask for a clean BIOS.

You can Also Check résistance to ground on plt_rst Line too.

PLT_RST to ground - 70k Ohm

Today I went through the voltages again and I noticed the board was missing 1.2V.
Then I found that there was a short on 1.2V line (0.0 Ohm).


1. Where I noticed the short.
2. I removed the PUM1 controller and short was still there.
3. I injected 1V2A into the short and the part of the CPU circled in picture got warm.

Also, I was making measurements on PUM1 controller, and noticed, that when I was measuring voltage on PIN8, there would be a clicking/sparking (like a relay) sound coming from CPU. It measured 3.0V. In BoardView there should be resistors and capacitator connecting to SYSON, PG_2.5V and GND, but on board they are unpopulated.


Could the CPU be bad?

[pc_okay]

Hello,

You had SYS_PWROK - 3.3v in post 12, so at that time your 1.2v must be ok.
Do you loose SYs_PWROK now?

In BoardView there should be resistors and capacitator connecting to SYSON, PG_2.5V and GND, but on board they are unpopulated.

It's 0 Ohm résistance they often Forget thoses résistances and just jump the tracks. Just look Closer you Will see continuity.

Could the CPU be bad?

1.2v Line is used to power ram, try to remove ram and measure again.
You can try to open PJM2 and Check if short is still présent on both side of jump PJM2.


If short is gone try mcplslg123 suggestion, that really make sense With your problem.

[someonenotyou]

Hello,

You had SYS_PWROK - 3.3v in post 12, so at that time your 1.2v must be ok.
Do you loose SYs_PWROK now?

In BoardView there should be resistors and capacitator connecting to SYSON, PG_2.5V and GND, but on board they are unpopulated.

It's 0 Ohm résistance they often Forget thoses résistances and just jump the tracks. Just look Closer you Will see continuity.

Could the CPU be bad?

1.2v Line is used to power ram, try to remove ram and measure again.
You can try to open PJM2 and Check if short is still présent on both side of jump PJM2.


If short is gone try mcplslg123 suggestion, that really make sense With your problem.

The SYS_PWROK still has 3.3V present, but 1.2V line is still shorted.
I opened PJM2 jumper, and short was gone from PUM1 controller, but still present going to RAM slots and CPU.
I inspected RAM slots and everything seemed fine. But I did resolder all the PINs. Still shorted.

[pc_okay]

I guess cpu is dead or balls are shorted…
Last chance if you are lucky and have Good ultrasonic machine: you can try to clean the board.

[mcplslg123]

If the short on 1.2V line is on consumer side, CPU is for replacement for sure.