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laptop not starting on AC , power light on , I press on button & goes off instantly

By paulek ยท 12 replies
Sep 22, 2007
  1. Hi guys well I just hope someone with some electronics knowledge in repairing notebooks would help me out in here.
    I got a sager 5680 lappy, and when I plug the lap on AC power without the battery I turn on the unit and instantly goes off, ( I hear a low sparky noise like some sort of short circuit, when this happens the psu light dimms from rock solid ) .
    Now if you leave the unit with the battery charging you may be lucky and the battery will charge and the only way the unit works is with the battery on it's bay, as soon as you remove the battery boom unit shuts off.

    The Unit does work but only when you plug in a battery and when it charges if you leave it dunno a couple of nights never gets solid green

    What I did :

    - Could the PSU be bad not throwing enough amps ? even if it shows voltage
    on digital meter

    - This lap has a separate voltage daughtercard for the battery I removed it when diagnosing this card goes
    plugged onto the mainboard and here the battery gets plugged.

    - Measured PSU voltage it's working fine 20volts DC

    - Checked SMD fuse on motherboard , fine

    - Dissasembled the entire unit ripped everything off that might me faulty

    - I've read the AC plug sometimes get's broken and I retouched the solder points, once I did this, by miracle the unit started without the battery plugged on. But guess what after I assembled the unit then again , when on AC power alone turned on , and then went off . So I don't know if the problem is on the AC female plug . What I do know is there's some sort of short circuit somewhere I hear like a sparky noise really low.

    This is really getting me crazy cause I do know the lappy works , but it's not working on AC by some reason it's not dead.

    I can take some pictures if someone can guide me through it I do have some knowledge about electronics and soldering
  2. raybay

    raybay TS Evangelist Posts: 6,908   +10

    The power adapters and the power sockets have an extremely high failure rate in the Sager 5680 laptop. We have seen eight of them in our shop with identical symptoms. While still under warranty, Sager replaced those without a question.

    The problem appears to be where the power meets the motherboard. New parts would need to be re-soldered into the system... expensive because it is very time consuming.

    Sorry I don't have a solution for you. Working units are available on eBay, if you want to trace the problem between a working model and a failed one.
  3. Tmagic650

    Tmagic650 TS Ambassador Posts: 17,231   +234

    It is not that difficult to resolder or to replace DC jacks in most laptops. I have done many of these type of repairs for around $125-$175 depending on model
  4. raybay

    raybay TS Evangelist Posts: 6,908   +10

    This is not a simple "jack" problem if his Sager 5680 problem is like the other we have seen. It is a chip. Replacing jacks never once helped. When we sent computer to Sagar under warranty, they just sent a new laptop... and never asked for the other back if we exchanged the hard drive.
  5. paulek

    paulek TS Rookie Topic Starter

    Hi ray thanks so much for your help, you know something I'm suspecting it's the dc jack that might have cracked in the middle layer of the pcb, cause I retouched the solder points at the bottom of the PCB and the unit worked without a battery on it's bay. ( just once happenned )
    This it's really strange the unit itself does worki it's not dead, if you place a battery on it's bay it works, something I might add to all this , I measure the voltage coming across the pinouts of the battery connectors and it's pumping around 1.5volts on each pin is this fine?

    I will remove the DC jack entirely ,when I buy some desoldering tape and maybe I'll just solder some cable cables between the PCB holes from top to bottom , if there was some kind of crack this would help. I was going to get some desoldering tape today but I just forgot.
    The strange thing is I did make this damn lap work when I did touch the solder points of the DC jacks buy once I assembled the unit again , didn't work , maybe I did some tension on the pcb and this moved the positive pins of the dc jack who knows.
    Ray could you describe me the symptoms you had on your 5680 sagers to see if they compare to mine . Thanks
  6. Tmagic650

    Tmagic650 TS Ambassador Posts: 17,231   +234

    From what paulek said, pressure on the DC Jack might have damaged the motherboard. Your Sager experiences, might not be worth anything here, or anywhere else. There are no "chips" involved with this issue. I have replaced many DC jacks. Motherboards all have several layers. Among these layers are the ground plane, and the power supply layers. You have to have a hot soldering iron and work fast. Just the action of removing the DC jack can damage these layers.

    As I said, you need a hot soldering iron. I use a professional PACE MBT solder/desoldering station. Using plenty of heat and additional flux, the DC Jack can be removed and replaced without damaging the layers and trashing the motherboard. Again, you have to work fast and experience helps, as with anything. A lot of repair centers will replace the whole motherboard... Sager might have thought replacing the entire laptop was easier than replacing just the motherboard
  7. paulek

    paulek TS Rookie Topic Starter

    Hi Tmagic I see you have lots of experience in this area, to be honest I got a soldering gun "GOOT" brand 100-110W 32-35Wh , will I be able to desolder the jack using desoldering tape, removing all the solder and some flux as well?
    And something else, what do you think might have happened that time when I retouched the solder points from the bottom of the mainboard, and I plugged the DC plug the unit worked fine without any battery? , and afterwards when I assembled again the unit same problem again. Could some of the pins might have cracked?.
    Does my scenario match with any you've gone through? you say the are a couple of layers in between the pcb and some of those traces power the mainboard right? . To make it worse the DC plug has four pins in the middle some sort of stupid propietary plug from sager, It's not just one pin in the middle there are four of them, 2 If I'm not mistaken are ground and 2 are 20 volts DC.
  8. raybay

    raybay TS Evangelist Posts: 6,908   +10

    Sounds right. Good work. On ours, it may have been hairline cracks on the board... or a chip which we didn't attempt to fix because the clients didn't want to go for the extra expense. It may have been a brittle board, or impact damage.
    Also saw the same problem on two Sotec laptops which appeared to have the same motherboard.
    But you might be able to create connections since it is yours, and you are not working against deadline.
    I think the plugs you describe are European tech, in origin.
  9. paulek

    paulek TS Rookie Topic Starter

    hI ray well , I'm going to remove the jack from the PCB, and re solder it again, I hope this really helps. Maybe one of the pins it's not doing contact between one of the power feed trace .
  10. raybay

    raybay TS Evangelist Posts: 6,908   +10

    Good luck. We will be awaiting your followup.
  11. Tmagic650

    Tmagic650 TS Ambassador Posts: 17,231   +234

    The DC Jack usually has an outer ground ring and a center pin for the +20volts. There may be 3 or 4 ground pins (through the motherboard for mounting strength) and only 1 20 volt pin through the motherboard... I can cover the 4 or 5 pins at the same time using a chisel tip on the iron, with extra flux applied to the board. Gently wiggle the DC jack until the legs wiggle through the board. For stubborn pins, apply heat and more flux to the pin directly.

    To reflow solder, apply flux and heat, and a little more solder.

    Soldering rule: HEAT THE PART, NOT THE SOLDER. The parts heat will melt the solder, and let it flow. Heat is the key. My soldering station is set at tip temp of 700 degrees for this
  12. tipstir

    tipstir TS Ambassador Posts: 2,842   +193

    Wow you guys charge alot and have that much time to solider we just replace the entire MOBO and battery and call it a day. Move on to the next problem case.
  13. raybay

    raybay TS Evangelist Posts: 6,908   +10

    Except the motherboard is no longer available, and the case size is not standard, so others will not fit. I haven't seen one on eBay for a long time.
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