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Laptop Adapter voltage decrease when connected

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ngzek

Member
Laptop cannot power on, adaptor 19v become 1.4v when connected to laptop mother board(gateway sa1). Please suggest most suspectable components in the board. Thank you
 

ngzek

Member
Clarkdale44 yes I have tried with different adapter, result is same voltage at the power jack terminal become 1.4 to 2v. Also I have check any visible damaged in the motherboard but can't find.
 
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ngzek

Member
Battery-in positive and ground line shows shorted signal in multimeter but in power jack side positive and ground is not short.
 

vtech

Active Member
Battery-in positive and ground line shows shorted signal in multimeter but in power jack side positive and ground is not short.
While not familiar with the specific laptop, I had a similar issue with an application which used the MAXIM8724 controller IC.
Provided you are measuring the correct plus/minus battery pins, there should NOT be a short there. (Possibly shorted cap PC89?)
BAT+ line is constantly monitored by the IC to route the DC from the external adapter to keep battery fully charged.
Therefore, if/when there is low resistance/short detected on the B+ line, it can trigger the shut down within the IC. (No power due to shorted laptop batteries are common).
SA1 is rebadge for Gateway manufactured by Quanta computer and already posted online.
 

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ngzek

Member
Vtech thanks. We found pc92 and pd3 were shorted. After replacing these components this motherboard litup everything like normal but after some minutes all the light gone again. Please help
 

vtech

Active Member
Vtech thanks. We found pc92 and pd3 were shorted. After replacing these components this motherboard litup everything like normal but after some minutes all the light gone again. Please help
It does not sound like the same problem I was referring to earlier. Getting too involved in SMD computer motherboards can get very frustrating:banghead:
A quick look back at the schematic, based on your failed components and how it reacted afterwards, does not sound very promising;:sorry:

At this point I can not be sure as to how much more may be wrong and it is likely outside of the forums scope.
It is definitely not a good sign for both PC92 & PD3 to be shorted.:eek:
It looks as if at some point, there may have been a surge introduced through the DC jack or perhaps a wrong/defective adapter used? Was there any liquid spilled in the unit?..... I can tell you stories......

PD3 tied to the DC input jack is meant as a steering diode to the MAX8724 charge controller input pin. The only purpose is to provide a reference. (Since it was shorted, there is good possibility the IC itself is also zapped?)
Capacitor PC92 on the other hand is in the PWR_SRC (EMI filter) line. (Being shorted, there is no telling what else may be wrong tied to PWR_SRC line).

There is no easy way to determine the extent and all you can do is to troubleshoot further down the pipe.
Depending on your location in the world & how much time/money you are willing to spend it may turned out to be a lost cause.:arghh:
 

ngzek

Member
Cpu, North bridge and South bridge were found very hot. Ithink its normal but suddenly blackout. Thanks for your help vtech
 

spec

Well-Known Member
Most Helpful Member
Cpu, North bridge and South bridge were found very hot. I think its normal but suddenly blackout. Thanks for your help vtech
This is just some information chucked in gratis, but a computer which suddenly blacks out, as you mention, is often due to one of the chips overheating, normally the CPU.

Generally speaking power dissipation is a problem with CPUs, bridges, graphics chips, and other high dissipation chips. This is especially the case for laptops.

There are three areas:

(1) The contact between the chips and any heatsink.
(1.1) The clamp holding the chip in contact with the heatsink loses tension
(1.2) The insulating medium between the chip and heatsink degrades and becomes a high thermal resistance. Heat sink compound goes dry and brittle (this is very common after around two years of high use). You can normally improve on the factory fitted insulating medium and sometimes clamping.

(2) The fan cooling system is faulty.
(2.1) Ducting clogged with debris
(2.2) Fan bearing stiff or seized
(2.3) Thermal sensor faulty

(3) Solder joints crystallized by heat (especially on laptops). This is increasingly a problem with the lead free type solder being used now.
The only solution here is to reflow the solder joints or fit a new motherboard.

The net result of fixing the above problems, especially (1) and (2) has been, in my experience, to convert a quirky computer with all sorts of odd random faults into a stable reliable machine.
In one case a laptop would work OK with all programs except Photoshop- that led me on a wild goose chase.:p

spec
 
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