Bring Mainboard back to life

Discussion in 'General Electronics Chat' started by dpeterson3, May 25, 2010.

  1. dpeterson3

    Thread Starter New Member

    Oct 9, 2009
    My laptop has been experiencing power issues for a while due to a bad plug. I took it apart as per the service manual and removed the bad plug. In its place, I soldered some wires until such time as I get off my lazy butt and order a new one. The problem now is the machine will not boot or even confirm it is getting power. I used my volt meter to check power outs on the board. +3.3, +5, and +20 seem to be working (no idea what the +20 is for, but it is there). It just won't do anything beyond there. I have no idea where to look next and a new board is a bit expensive.
  2. flat5

    Active Member

    Nov 13, 2008
    Were you waltzing on a wool carpet while handling and soldering the board? I hope you did not damage it with static electricity.
  3. dpeterson3

    Thread Starter New Member

    Oct 9, 2009
    Found the problem. I had been using a generic power supply as I can't find the actual supply for this machine. I borrowed another supply rated for a voltage similar to the original (the generic one has the correct ratings but doesn't actually push the power it says it does) and tried it. Low and behold, the lights light up and the machine started to come to life, Then it started smoking a little because the borrowed supply was rated a little high. Unplugged immediately. If a modd wants to delete this post, its fine by me.
  4. retched

    AAC Fanatic!

    Dec 5, 2009
    I think it is a good post to leave up. It will help others who may consider doing the same by showing them the result without having to damage their machines.

    The 20v is probably there to charge the battery when needed. The mainboard has a charge controller with a comparator that reads the voltage on the pin to see when the external power is applied and when the battery needs charged.

    By using a higher rating you may have reached a breakdown voltage of one of the diodes resulting in a CHARGE COMPLETE mode, but the transistor switch could not "hold back" the extra voltage.

    This can easily result in a fire. Lithium batteries are VERY dangerous beasts.
    They will strike when taunted. The cage for these beasts are proper charge times, temperatures, and discharge rates.

    On the mainboard, the battery charge controller has an IC that regulates the battery charging voltage and current by sampling the conditions of the batterys voltage, current and temperature. I would suspect when you do find the proper plug and power supply, you will have either lost battery only mode, or no longer have the ability to charge the battery.

    If you are lucky, replacing the battery itself MAY remedy the problem, but it could also exacerbate the problem by feeding "new" battery juice to now damaged regulators.

    I would not leave this laptop charging overnight in an area where a fire could cause much damage. Keep an eye, and hand on this machine while charging. Unplug when you are not in eye range.

    The now weakened components could cause the lithium battery fail-safes to fail-unsafe at any given time.

    There is only so much 'magic smoke' in components. Once some is let out, you dont get it back, and a shortened life expectancy and non-typical function is to be expected.
  5. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    Looks like my area of expertise but I donno what experience OP has?