Acer helios 300 noob questions...

[darkness77]

I have this motherboard and it was shorted somewhere on main 19v line...or after...Finally after many desoldering and using boardview and schematic it was shorted mosfet on cpu power rail... Now its all ok but i have two noob questions:

1. Could i have used bench power supply and set it on 19v with 1 amp limit to main 19 v power rail to find what is hot or it would burn something on the way like cpu because it was shorted through the mosfet? I read many articlas and many forums...and some people are saying no,no,no, it is not good idea to use 19v on shorted motherboard on main power rail..and other says it is ok if you set limit to 1amp and that way cpu or gpu will not be destroyed? What do you think?

2. And second, why there is a difference in reading on bench power supply in a way...Let say if i set limit to 1.5 amp and short the probes it would show some value of voltage...and that is complete short (two probes touching) but if i apply those probes to a short to gnd rail on the motherboard it will show different voltage? And that rail is also shorted to gnd (0 ohms) but it will show different voltage...meaning there is resistence?? But how if it is shorted?
Thx for answers.

[piernov]

Re: Acer helios 300 noob questions...

https://www.badcaps.net/forum/showthread.php?t=88758

2.4. Never inject 19V
If the 19V main power rail is missing, there's a reason, often because a protection kicked in to avoid more damage. For example, the 19V power rail could be shorted to the CPU through a bad high-side MOSFET. In that case, the charging circuit protection kicks in and turns off the DC-in MOSFET. With enough luck, the CPU didn't take too much of a hit yet. If you inject 19V, you are sure to destroy it.
Always measure exact resistance to ground to see if there is a possibility of high-side MOSFET short. Always start at 1V and check if any of the large BGA (CPU/GPU/PCH) is warming up. Monitor the power consumption.

[darkness77]

Re: Acer helios 300 noob questions...

I understand what you say...but i have read and seen many times people saying different...so i am.bit confused...And they are not noobs like me. I am not saying you are wrong...just want to clear things out....for example on this video the repair guy is saying its safe to apply 19v if used with low current ..If you dont want to watch whole video...go from 19:00 .... https://youtu.be/WU8_eTglue0

And can someone answer to my second question? Thx

[Sephir0th]

Re: Acer helios 300 noob questions...

There is No need for me to watch the vid, because this is a General Rule in (Laptop) Chip Level. What piernov shared is the truth. When you inject 19V when High Side mosfet is Short, Most likely bad Things will Happen.

Personally i saw many Boards, died this way.