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Laptop dead on but works on battery- power adapter fine

Last response: in Laptops & Notebooks
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July 11, 2010 9:06:43 AM

Hello,

I have a problem with my Asus f3s laptop.
It starts up perfectly fine on the battery (windows screen and everything), but when i want to start it with the adapter the lights go on for a sec and that's all it does. From my understanding, this means that the motherboard is not fried- as it works on battery, right?! (So it should actually be something easy to repair...?)

I measured the adapter with a voltmeter and it's fine.
So I dissembled the laptop to check the power jack. The solder connections seem fine, and measured with a voltmeter it gets the 19.6V as well (and drops to 9V then up to 15V and back to 19 within 1-2 secs when start button is pressed- with no battery). So, the connection between power jack and start button isn't the problem either...
But now i'm running out of ideas. Is it worth replacing the power jack anyway or what could be the problem ??

I really hope you have some more ideas, suggestions :) 

Cheers
Chico
a b D Laptop
July 11, 2010 3:15:16 PM

Your problem is one of two.

(1) The power converter circuit in the laptop is Bad. This is the circuit that converts the 19.3 volt output to a lower voltage needed to run the laptop computer (ie laptop battery is only 10.8 Volts (uses slightly higher voltage when charging.)

(2) Your "brick" is bad. In your case the power pak is showing the correct voltage with No load (or very low current). However, when you apply a load to it the output voltage drops all the way down to 9 V. This indicates that either the Power pak is failing (can not supply rated current at rated voltage), or the Input current is too high (above stated specs - ie Mine indicates 19 V at 4 Amps). If the input circuit in the laptop has failed in a manner that when the power pack is plugged in and the power button is pressed the current exceeds the power pack rating, the voltage is reduced and the system powers off - Then current is reduced and the power pak voltage goes back up to normal.

The simplest way to isolate is to (1) replace brick or (2) measure your power pak with a load on it. Problem with getting the load is finding a resitor(s). 6 one ohm/10 watt resistors in series would give you 3.33 Amps (67 Watt load). Or you could get several 12 Volt lamp bulb ( car bulb ) and put several in parralel to equal about 50 watts. Reason it might be just as cheap and simpler to just replace brick.
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July 12, 2010 1:53:14 PM

Thanks for the answer.
If it is the first one and the circuit is bad, is there actually anything to be done? Except using it for parts and dumping the rest? Or getting 2 spare batteries and an external charger to run it on- which is prob as expensive as buying a new one....

Just to clarify the vocabulary (i'm not native english speaking...):

brick= battery
power pak= Ac adapter

I also should add: I tried to start the computer without the battery only on ac-adapter, when the voltage dropped that far. So the decrease was independent of the akku...
I usually used the pc anyway on ac as i hardly travel with it- and the akku wasn't the best before...

About the bad power pak: a new bougth one shouldn't show those problems anymore, right?
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a b D Laptop
July 12, 2010 2:46:30 PM

Brick=power pack=AC Adaptor

Yes, I would first try replacing the power pak - that is probably the cheapest route. You might be able to go to a go to a store and try one with the understanding that if it fixes your problem you will buy it. (NOT the most ethical - buy a power pac, try it and if it does not work return it)

As to repair: If a replacement power pak does NOT fix problem. Alot depends on your (1) electronic knowledge in tracing the circuit (hard to get schematic drawing, and (2) your ablity to desolder and solder in a replacement part on a multilayer circuit board. An alternative would to find a shop/store that will do it at a resonable cost.

If you wanted to go the route of two batteries and an external charging system. Computer batteries generally run 50 -> 100 bucks here in the states. Next the hard part may be an external assembly to plug your battery into. You could not plug the battery direct to the AC adaptor. As I pointed out the adaptor voltage is too high and must first go to a circuit to reduce the voltage. This circuit also monitors the charge status of the battery and adjusts the charging current as the battery approaches full charge.
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March 12, 2013 4:56:44 AM

i thing its adoptar prob.. if u another same one than try...
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