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Dc power jack multimeter test

Last response: in Laptops & Notebooks
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February 10, 2010 3:54:37 AM

I have an Asus G50 that receives no power at all, no lights no nothing. So I tested the AC Adapter with a multimeter and it is fine. I disassembled the laptop to the motherboard to look at the DC Power Jack and, though I do not exactly know what a bad power jack looks like, on this one the solder pins are not discolored or broken. I want to test the voltage at the DC Power Jack to see if the power jack is bad (or not receiving power). So, I was going to plug the AC power adapter into the jack and put the multimeter on the DC Jack to see if it reads 1.9 volts, but I don't know what DC Jack pin is the positive and which is the negative and I'm afraid I'll short the motherboard if I touch the wrong pins.

Can anyone help me determine which pins to test with the multimeter?

Thanks.
a b V Motherboard
a b D Laptop
February 10, 2010 4:09:03 AM

The lead connecting to the center of the jack is generally positive, while the other is ground. Reversing them and connecting your multimeter won't hurt it, though...it'll just read a negative voltage.
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February 10, 2010 4:51:21 AM

Thanks. The multimeter shows 19.7 volts (and yes it showed -19.7v when reversing connectors) while plugged into the AC adapter. Does this mean that my dc power jack is good for sure. If so is there a way to test if the motherboard is fried, or shorted, or whatever.

Thanks.
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a b V Motherboard
a b D Laptop
February 10, 2010 2:44:16 PM

I assume you tried powering on with and without the battery installed. A bad Battery can prevent powering on, even when using a brick.

2. Requires two people - While monitoring the voltage at the jack, try powering on the laptop Remove the battery and the Hard drive first. (Hard drive is not required, but I would as a precaution.). The output from the Brick should drop from the 19.7 Volt unloaded condition. Not sure how much, best quess is 1 to 2 Volts. If it does not then The laptop is Not trying to power on - several possibilities. Power button, MB not providing an "I'm OK" signal, Memory, and or GPU, Power converter in laptop to convert the 19.7 Volt brick output to +12V/+5V (This last one is best QUESS).
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a b V Motherboard
a b D Laptop
February 10, 2010 2:48:56 PM

It depends on where you measured it to show connectivity. When you use your probes, you should be sticking them to the contacts on the underside of the PCB, not on the jack itself. Did you do this?

And, yes, try powering on the notebook while watching the voltage drop (from any location will work for this). If it drops, your notebook did something. If not, you may have a bad button or a bad board. Try bypassing the button by shorting it's contacts on the underside of the PCB where it resides (if it's not surface mount).
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February 10, 2010 8:47:27 PM

Thanks Frozenlead and Retiredcheif for your replies. I have the motherboard completely removed with just the processor on it, but I guess I can connect the powerbutton board ribbon cable back to the MB to do the power test you suggested. Frozenlead forgive my ignorance but what is PCB (is that power connector board?). If so, is that the same as the power button board? I have the power button board which connects to another small board that connects to the MB via a small ribbon cable. I am confused how I would test the power on that. What I did was put the multimeter where the power jack is soldered to the MB, so the power jack underside is soldered to the MB with 6 solder dots, 4 of those are just the power jack legs so to speak and I assume the other 2 are the positive and ground connectors, that is what I tested with the multimeter, and it showed that I was getting 19.7v, does this mean that the powerjack is good and not the problem?

How can I bypass the power button by shorting it, I know how to do this on a desktop you simply put a flathead screwdrive on the 2 pins that connect to the power button, but on a laptop I'm lost. As mentioned the powerbutton connects to a small board about 2x the size of a postage stamp, this board connects to a small thin board via a ribbon cable, and then on this board there is another ribbon cable that connects to the MB. How can I short that ribbon cable connector on the MB to simulate the powerbutton on?

Thanks much
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a b V Motherboard
a b D Laptop
February 10, 2010 9:44:26 PM

PCB = printed circuit board. You've been referring to it as simply "board". Either is fine. The acronym has less letters to type, and I'm lazy.

By the sounds of it, you tested the jack correctly. Note, though, that your test does not rule out the jack being loose still, but that's a more difficult test, and if it works in one position, that's good enough for now.

The power button also rests on a PCB. You will have to plug in the ribbon cable to the motherboard (make sure you install 1 stick of memory and your CPU/GPU heatsink if you have them removed!), plug in your adapter, and hit the power button. If nothing happens, turn the power button PCB over, and find where the button's contacts are (should be right beneath it). You should see two copper dots - connect them in some manner with a piece of metal, just like you would do with a desktop computer. If the machine boots, your button is bad (I doubt it is, but you can test it anyway).
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February 11, 2010 5:21:07 AM

I highly doubt the jack is bad....its two strips of metal which connect the adapter to the traces on the PCB.....it's possible that it came loose, but adapters are usually through hole soldered, and it is difficult to dislodge that.....
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a c 156 V Motherboard
February 11, 2010 3:51:28 PM

But not impossible. Kittens knocked one of my laptops off its stand last year. Broke the power jack on the brick. Also broke the power connector on the laptop. Computer runs, but doesn't charge.
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February 11, 2010 5:03:18 PM

The power jack is not loose at all, it if firmly soldered to the MB. And I tested the power button according to Frozenlead's advice and still nothing. I guess the MB is bad. Oh well, I don't think I'll be able to find a replacement MB for cheap so looks like this laptop is scrapped.
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February 22, 2010 9:53:58 AM

Hi tilopa88! You repair Your laptop or no. What was the problem? I have the same problem - no power.
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March 2, 2010 4:30:07 PM

My problem seems to be more extensive than just the power jack. And no I was not able to repair it, it is dead in the water.

You might try taking it apart down to the mother board and inspecting the power jack, if the solder points are black or the jack itself is loose then your problem is the jack needs to be resoldered and that is not a difficult fix.

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June 30, 2010 4:39:40 PM

Hello,

I have a similar problem with my asus laptop.
The AC adapter is fine, took the notebook apart and measured the power jack- it shows 19.7 as well. The piece isn't loose neither look the solderings damaged.
BUT the computer starts up on battery- it does nothing/ sometimes let's the lights blink for a second on AC.
Which makes me wondering, what else it could be?
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August 11, 2012 10:38:58 PM

chico_13 said:
Hello,

I have a similar problem with my asus laptop.
The AC adapter is fine, took the notebook apart and measured the power jack- it shows 19.7 as well. The piece isn't loose neither look the solderings damaged.
BUT the computer starts up on battery- it does nothing/ sometimes let's the lights blink for a second on AC.
Which makes me wondering, what else it could be?



Quote:
Did you ever find out what caused the problem? I have a Dell Inspiron 6000 with the same problem. It fires up on a charged battery. Attach the brick when the computer is running on battery and the brick goes dead (light begins to dim till it is out) this takes <5 seconds. I have replaced the dc jack and have power on both sides of the jack. The brick passes for power. I have tried three adapters and none will power the computer up. A charged battery is the ONLY way the unit will operate. Seems to rule out motherboard issues since it works with the battery??
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January 4, 2013 6:23:57 PM

It seems Chico out of all these techs or techies you can receive no answer to this mystery. Neither I have it but it bugs me like it's my computer. I would like to know the solution to this mystery. Please let me know if you find the answer. Thanx and if there is anything else I can see what I can do for ya.

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a b D Laptop
January 5, 2013 10:00:31 PM

This topic has been closed by Buwish
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