Short on motherboard power rail - general question

[Askic]

Hello guys,
first of all I'm not a professional in repairing electronics, but I do have formal electrical background. From time to time I have managed to repair something like PSU or laptops when faults were obvious or very easy to find with a multimeter.

However, recently I had a problem with 19V power rail shorted to ground. I was not able to find the cause, because a shorted component was somewhere deeper in the motherboard and this was handed to a professional.

I wonder if it is sufficient to check 8th pin on BIOS chip and pin on power switch, where 3.3V is expected and to test it against the ground to conclude that short is not on 3.3V rail?

Since 3.3V is produced from the main 19V, it is reasonable to assume that short on 3.3V can appear like short of 19V rail.

Thank you.

[stingerchamp]

Re: Short on motherboard power rail - general question

Hi,

First of all , you don't have to be professional to understand gate , voltage or any signal processing
You need basic understanding of MOSFET, signals , resistor, capacitor, and basic motherboard voltage level processing etc.

Read basic tutorial given in this forum and you will understand

19v is connected to all linear drive ic, switch ICS and all other etc. The main point where it is going out in motherboard from DC in section or charger ic section in general is a CLR , current limiting resistor.

Remove it and check resistance to ground on CSP and CSN

This will give you idea if short is on DC in MOSFETs side or 19v out or edge side.

Read guide you will understand.

Short can be due to vin section as it is spreading in motherboard.

[Askic]

Re: Short on motherboard power rail - general question

Hi,

First of all , you don't have to be professional to understand gate , voltage or any signal processing
You need basic understanding of MOSFET, signals , resistor, capacitor, and basic motherboard voltage level processing etc.

Read basic tutorial given in this forum and you will understand

19v is connected to all linear drive ic, switch ICS and all other etc. The main point where it is going out in motherboard from DC in section or charger ic section in general is a CLR , current limiting resistor.

Remove it and check resistance to ground on CSP and CSN

This will give you idea if short is on DC in MOSFETs side or 19v out or edge side.

Read guide you will understand.

Short can be due to vin section as it is spreading in motherboard.

Hello stingerchamp and thank you for your reply. Can you post a link to the tutorial you meant? I have read the basic guidelines here.

[stingerchamp]

Re: Short on motherboard power rail - general question

Yes same tutorial but CLR info is not mentioned instead DC in section is mentioned, CLR is part of DC in section.

If you have any question , you can write, I will answer

[stingerchamp]

Re: Short on motherboard power rail - general question

Hello guys,
first of all I'm not a professional in repairing electronics, but I do have formal electrical background. From time to time I have managed to repair something like PSU or laptops when faults were obvious or very easy to find with a multimeter.

However, recently I had a problem with 19V power rail shorted to ground. I was not able to find the cause, because a shorted component was somewhere deeper in the motherboard and this was handed to a professional.

I wonder if it is sufficient to check 8th pin on BIOS chip and pin on power switch, where 3.3V is expected and to test it against the ground to conclude that short is not on 3.3V rail?

Since 3.3V is produced from the main 19V, it is reasonable to assume that short on 3.3V can appear like short of 19V rail.

Thank you.

first step make sure 19v available in motherboard
Second step make sure 3v ic ldo is generated


Short on 3v does not mean there must be fault on 19v

[Askic]

Re: Short on motherboard power rail - general question

first step make sure 19v available in motherboard
Second step make sure 3v ic ldo is generated


Short on 3v does not mean there must be fault on 19v

Hello stingerchamp, even after reading the beginner guidelines again, I'm not sure what CSP and CSN are since these abbreviations are not mentioned in the text.

However I hope you'll be able to show me on the real world example. Recently, I have successfully repaired motherboard by sheer luck because faulty (shorted) cap had black marks and was short to ground. When I removed this cap everything worked OK.

Here on the attached picture one can see charging port connector and battery connector.
Can you please tell me what is the CRL in this picture?
I know that CSP and CSN are probably outputs from IC battery charger chip.
I assume that this IC is on the other side of the board and that CLR is actually R889.

[stingerchamp]

Re: Short on motherboard power rail - general question

It is in every motherboard

It is just a name of pads of a current limiting resistor or power resistor

Current sense positive csip
Current sense negative csin

These are pins 1,2 of a charging ic through which
Charging ic check correct current sensed or not

[Askic]

Re: Short on motherboard power rail - general question

It is in every motherboard

It is just a name of pads of a current limiting resistor or power resistor

Current sense positive csip
Current sense negative csin

These are pins 1,2 of a charging ic through which
Charging ic check correct current sensed or not

Ok thank you. so these two pins are labeled ACP and ACN on the schematics you attached. I understand now.