DC Jack

[Tech bud]

Hey everyone. I got a laptop in the wouldn't power on. I had test the DC jack and it was only getting .01 volts through the jack. So I thought DC jack, luckily it was a replaceable one, so order it and came in today.

Plugged it in to my charger and tested before install, getting 19v like it should, plug it all back in. Computer still doesn't boot. I test the leads that the dc jack plugs in to, but only getting .33 volts to the motherboard. Is it possible that both the motherboard and jack went bad?

or does anyone have any ideas or experience that might be the culptrit. Just seems like some bad luck for it to test bad and not be that?

 

[Tech bud]

Trying to take everything out one by one now

 

[Tech bud]

Does that sometimes happen though if the dc jack tests fine, replace then its still the motherboard?

 

[Larry Sabo]

Why would you replace it if it tests fine?

 

[Tech bud]

It wasn't testing fine originally. When I installed the new one it tested fine. Then I plug it in the motherboard, it loses all power on the leads to motherboard.

So out of motherboard 19v, in motherboard, socket shows .33 volts

 

[glennd]

Hey everyone. I got a laptop in the wouldn't power on. I had test the DC jack and it was only getting .01 volts through the jack. So I thought DC jack, luckily it was a replaceable one, so order it and came in today.

Plugged it in to my charger and tested before install, getting 19v like it should, plug it all back in. Computer still doesn't boot. I test the leads that the dc jack plugs in to, but only getting .33 volts to the motherboard. Is it possible that both the motherboard and jack went bad?

or does anyone have any ideas or experience that might be the culptrit. Just seems like some bad luck for it to test bad and not be that?

you're not getting .33 volts to the motherboard, you're getting .33 volts *at* the motherboard. The only sensible test of the jack is to disconnect it from the motherboard and test if the pins have the same potential as the charger that is plugged into it. If you are then the jack is probably alright. Once it's plugged in to the motherboard and switched on, any short on the power input side of the motherboard will drop the input potential to nearly 0 volts which you'll be able to measure from the motherboard back to the jack. And if you leave it like that you'll eventually fry the secondary side of the charger.

So out of motherboard 19v, in motherboard, socket shows .33 volts

You're misreading the situation. Because you now have a direct electrical connection from the jack to the motherboard, whatever the potential is at the motherboard is what you will measure on the jack. In other words your .33 volts represents a fault on the motherboard.

 

[Larry Sabo]

I had test the DC jack and it was only getting .01 volts through the jack.

That's not how you test the DC jack. You put a test probe on the input side and measure the resistance to the output side. A real pain but measuring the output voltage is inconclusive, since a MB fault can be responsible for a low output voltage, as well as a bad AC adapter.

 

[Tech bud]

you're not getting .33 volts to the motherboard, you're getting .33 volts *at* the motherboard. The only sensible test of the jack is to disconnect it from the motherboard and test if the pins have the same potential as the charger that is plugged into it. If you are then the jack is probably alright. Once it's plugged in to the motherboard and switched on, any short on the power input side of the motherboard will drop the input potential to nearly 0 volts which you'll be able to measure from the motherboard back to the jack. And if you leave it like that you'll eventually fry the secondary side of the charger.


You're misreading the situation. Because you now have a direct electrical connection from the jack to the motherboard, whatever the potential is at the motherboard is what you will measure on the jack. In other words your .33 volts represents a fault on the motherboard.

I believe were on the same page then. The DC jack is a removable jack that has a cord that runs into the motherboard. They have the metal pins that show and I tested the voltage there on the original one. It showed no voltage going to that point. I ordered a new part.

When the new part came, before I even plugged it in, I just plugged it in to the the AC adapter and tested right away to make sure working. It test at 19V at the end of the jack. Plugged it in to motherboard, no power.

Where the DC jack plugs into the motherboard, at the solder joints, only get .33 volts with good dc jack. Bad motherboard? I was thinking its bad too as what else could it be. But was like maybe there is something I am missing that I don't know.

 

[Tech bud]

That's not how you test the DC jack. You put a test probe on the input side and measure the resistance to the output side. A real pain but measuring the output voltage is inconclusive, since a MB fault can be responsible for a low output voltage, as well as a bad AC adapter.

I didn't know this, all instructional videos I could find had me checking only volts coming through all the parts?

 

[Tech bud]

This is the video I followed along with to make it easier, was the same reading.

 

[Larry Sabo]

This is the video I followed along with to make it easier, was the same reading.

If you followed the video exactly, the connector from the DC jack was not connected to the MB, and should have measured 19.5v. Are you saying that you measured it disconnected from the MB and it measured 0.1v? Are you sure you had a good connection between the probe and the plug, and used both probes on the plug? If so, then both the DC jack and the MB would be at fault, assuming you confirmed the output of the DC adapter is 19.5v when disconnected.

 

[Tech bud]

If you followed the video exactly, the connector from the DC jack was not connected to the MB, and should have measured 19.5v. Are you saying that you measured it disconnected from the MB and it measured 0.1v? Are you sure you had a good connection between the probe and the plug, and used both probes on the plug? If so, then both the DC jack and the MB would be at fault, assuming you confirmed the output of the DC adapter is 19.5v when disconnected.

Yes, i first measured the ac adapter is getting 19v, then I measured the unplugged dc jack with ac adapter plugged in at the ends like the video, and they read .01v. Now with new DC Jack, it reads 19v, but plugged in at the motherboard solder joints, it reads .33 volts.

 

[Larry Sabo]

Lousy luck then. Both DC jack and MB defective. Awkward to deal with, with the customer, but that's what I believe is the case.

 

[Tech bud]

I think I messed up somewhere, I usually avoid power issues like this, but watched enough videos was like I got this. I think I will give the customer a warning next time that, although I think its the jack. I could still could be possible that its the motherboard, will not know unitl the new jack is installed

 

[glennd]

I believe were on the same page then. The DC jack is a removable jack that has a cord that runs into the motherboard. They have the metal pins that show and I tested the voltage there on the original one. It showed no voltage going to that point. I ordered a new part.

When the new part came, before I even plugged it in, I just plugged it in to the the AC adapter and tested right away to make sure working. It test at 19V at the end of the jack. Plugged it in to motherboard, no power.

Where the DC jack plugs into the motherboard, at the solder joints, only get .33 volts with good dc jack. Bad motherboard? I was thinking its bad too as what else could it be. But was like maybe there is something I am missing that I don't know.

You want to test the current going through the jack to the motherboard. That will show if there is a short on the board. Insert your multimeter into the positive circuit between the jack and the motherboard, switched to the DC Current setting. If you see something like 3 or 4 Amps DC, depending on the capacity of the charger, you know you have a short circuit.

Are you sure you have the correct charger for the laptop? I ask because some companies like to reverse the polarity of the DC output on the charger. Normally you have positive on the center pin and negative on the sleeve but sometimes they do the opposite and that will be problematic for you. Laptops generally have a sticker on the case showing the required charger specs.

 

[glennd]

Lousy luck then. Both DC jack and MB defective. Awkward to deal with, with the customer, but that's what I believe is the case.

I'll add to the confusion (but better for the customer) to say that a faulty jack may well have been the cause of the fried motherboard *and* the reverse is also conceivable, that is the faulty motherboard with the full short may well have fried the jack, although that seems less likely. Certainly a damaged jack can kill the motherboard. And you, the technician won't know the full extent until you get a working jack in place.

although I think its the jack. I could still could be possible that its the motherboard, will not know unitl the new jack is installed

See, all is not lost. It was a valuable learning experience

So you've probably done the best you could in the circumstances but in the end you're left with a dead laptop.

 

[glennd]

A masterful understatement.

Thank you!

If you've managed to reverse the polarity of the neutron flow then you've destroyed the motherboard. Please don't have done that.

and we all know where that will lead...

 

[glennd]

But bear in mind that if you get a reading of zero it's probably because you've just blown the fuse in your multimeter. Most non-specialist meters will handle up to 10A or so, but if you have a dead short on the motherboard then it's possible that the PSU is pumping out more than that.

true but we're talking about a laptop charger which is not going to deliver more than 4 or 5 amps dc without cooking your breakfast. For example, your typical Toshiba charger is rated at 19VDC, 4.74A = 90W.

 

[Larry Sabo]

I'll add to the confusion (but better for the customer) to say that a faulty jack may well have been the cause of the fried motherboard *and* the reverse is also conceivable, that is the faulty motherboard with the full short may well have fried the jack, although that seems less likely. Certainly a damaged jack can kill the motherboard. And you, the technician won't know the full extent until you get a working jack in place.

I don't know how either could happen, actually. The most the jack can do is deliver 19v to the motherboard. If it's shorted, it delivers nothing to the motherboard, which wouldn't damage the MB. So, I don't see how a faulty jack can damage the motherboard.

If the jack and/or motherboard is shorted, they should cause the AC adapter to clamp the current and reduce output voltage. Personally, I don't see this damaging the DC jack.

If the adapter is faulty and delivers more than 19v to the jack, it could blow a chip on the MB if it can't regulate the excess voltage and might load the DC jack beyond its current-carrying capacity and fry something within it. In that case, the faulty AC adapter blew the MB and DC jack.

My bet is that the DC jack had a very poor connection where the centre pin connects to the cable. I've seen really poor connections between the centre pin and the tab that connects the pin to the MB but that's a different style jack.