Jump to content


 


Register a free account to unlock additional features at BleepingComputer.com
Welcome to BleepingComputer, a free community where people like yourself come together to discuss and learn how to use their computers. Using the site is easy and fun. As a guest, you can browse and view the various discussions in the forums, but can not create a new topic or reply to an existing one unless you are logged in. Other benefits of registering an account are subscribing to topics and forums, creating a blog, and having no ads shown anywhere on the site.


Click here to Register a free account now! or read our Welcome Guide to learn how to use this site.

Photo

Power at dc jack but not at the board


  • Please log in to reply
5 replies to this topic

#1 Bascotie

Bascotie

  • Members
  • 17 posts
  • OFFLINE
  •  
  • Local time:06:51 AM

Posted 14 June 2014 - 01:34 PM

Hi guys,

 

I'm working on an acer aspire 5750 laptop which does not turn on.

 

I can get 19V at the dc jack end connector (the side that plugs into the motherboard), but as soon as I plug it into the motherboard and try to measure for 19v at the motherboard end, it goes down to about .40v. I am assuming this is a bad motherboard issue but wanted a second opinion. Thanks!


Edited by Bascotie, 14 June 2014 - 01:34 PM.


BC AdBot (Login to Remove)

 


m

#2 Chris Cosgrove

Chris Cosgrove

  • Moderator
  • 5,973 posts
  • OFFLINE
  •  
  • Gender:Male
  • Location:Scotland
  • Local time:02:51 PM

Posted 14 June 2014 - 06:08 PM

Measuring 19V at the tip of the lead gives you the off-load voltage from the power supply. Once you plug it in it comes under load and you would expect a drop to somewhere between 17 - 18V.

 

The 0.4V you quote could have two causes, only one of which involves the mobo. This one could be a faulty / broken motherboard connector (where the jack goes in) and this is by no means uncommon but can sometimes be repaired by careful use of a soldering iron. Some laptops have the socket connected to the mobo by a cable and these are easy to repair - just replace the socket.

 

The other possible fault, which you don't seem to have considered, is a faulty DC unit. If this has cooked, and it can happen, it could still give you normal off-load voltage but drop to virtually nothing when it comes under load.

 

I would check this first because it is much easier to do than pulling out a mobo !  Substitution is the easiest way to test. See if you can find somebody with a similar Acer laptop and try your power supply in their laptop and theirs in yours. Failing that, you will have to rig up some sort of dummy load by getting a resistor across the tip. A 220 to 560R should do the job nicely.

 

Chris Cosgrove



#3 Bascotie

Bascotie
  • Topic Starter

  • Members
  • 17 posts
  • OFFLINE
  •  
  • Local time:06:51 AM

Posted 14 June 2014 - 06:11 PM

Measuring 19V at the tip of the lead gives you the off-load voltage from the power supply. Once you plug it in it comes under load and you would expect a drop to somewhere between 17 - 18V.

 

The 0.4V you quote could have two causes, only one of which involves the mobo. This one could be a faulty / broken motherboard connector (where the jack goes in) and this is by no means uncommon but can sometimes be repaired by careful use of a soldering iron. Some laptops have the socket connected to the mobo by a cable and these are easy to repair - just replace the socket.

 

The other possible fault, which you don't seem to have considered, is a faulty DC unit. If this has cooked, and it can happen, it could still give you normal off-load voltage but drop to virtually nothing when it comes under load.

 

I would check this first because it is much easier to do than pulling out a mobo !  Substitution is the easiest way to test. See if you can find somebody with a similar Acer laptop and try your power supply in their laptop and theirs in yours. Failing that, you will have to rig up some sort of dummy load by getting a resistor across the tip. A 220 to 560R should do the job nicely.

 

Chris Cosgrove

 

Thnaks Chris. I forgot to mention some of my other testing:
 

I had 2 brand new plug in type dc jack replacements in stock that fit this laptop, and neither of those worked.

 

The power adapter measured 19v fine.

 

I tried powering it on using the power button, as well as by manually shorting the power button solder connections, neither of which worked. 

 

So since the power adapter is good, and the dc jack is new, and the power wont come on in 2 different ways, I assume the motherboard is left. Is that correct?



#4 Chris Cosgrove

Chris Cosgrove

  • Moderator
  • 5,973 posts
  • OFFLINE
  •  
  • Gender:Male
  • Location:Scotland
  • Local time:02:51 PM

Posted 14 June 2014 - 06:33 PM

Only one other possibility that comes to mind - the laptop battery could be cooked. Have you tried starting the laptop just on DC power and without the battery?

 

If that doesn't work, then your first fears are probably correct - it's the mobo !

 

And just a note on the side - you almost never need to quote a complete post in a reply. Posts stay in the topic forever - with very rare exceptions. By all means use quotes to highlight particular points in a previous post, but there is no need, normally, to quote the whole thing.

 

Chris Cosgrove



#5 Bascotie

Bascotie
  • Topic Starter

  • Members
  • 17 posts
  • OFFLINE
  •  
  • Local time:06:51 AM

Posted 14 June 2014 - 07:07 PM

Thanks, the quote was indeed unnecessary .

 

I did try with just the power.

 

In fact, I tried it with this simple configuration:

 

- Motherboard out of the laptop

- 1 stick of memory

- tried 2 different new dc jacks

- power plug coming into the dc jack

 

No boot. Guess it was the mobo, thanks :)



#6 Chris Cosgrove

Chris Cosgrove

  • Moderator
  • 5,973 posts
  • OFFLINE
  •  
  • Gender:Male
  • Location:Scotland
  • Local time:02:51 PM

Posted 15 June 2014 - 09:11 AM

Ouch !  Sounds like either an expensive repair or the scrap heap coming up.

 

Don't worry about the quote. The basic principal is if you need to quote something - for example to make clear exactly what you are replying to or commenting on - then do so, but don't quote more than you need to, it saves page space and means we can get more replies on one page. Some of the topics on BC are 20 - 30 pages long and trying to get a grip on who said what is not easy !

 

Chris Cosgrove






0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users