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Intermittent power PEW71 LA-5894P Mobo Acer 5742G

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    Intermittent power PEW71 LA-5894P Mobo Acer 5742G

    It will randomly accept power, and also charge the battery usually only after the device has been turned off for an extended period of time. Usually it will charge the battery to about 25% before it shuts off the charging, and power through the DC jack.

    I first thought it was a software issue, but I've taken the battery out and had it directly on the adapter, and it was fine for about 15 mins then it just shuts off, and no longer accepts direct power. I tested the device on another charger inside an electronic store making sure it was within the specific standards. This also didn't work, but we got flickering as we put the DC jack in so I tired replacing the DC jack, and It's still doing the same thing.

    So after some further troubleshooting, and downloading a schematic I couldn't find many of the part numbers on the board. I just went hunting with my multimeter to see what I could find.

    I noticed that on PJP2 when the power was on pins 1, and 2 would raise from 0.0v to a max of 0.45v at which point if the board ever reached 0.46v the board would power cycle or even shut off for a few mins. So I traced the connection back looking for an unstable connection I kept seeing this 0.45v so I found the one part in the connection with a constant input, but a moving output. I found a R36W 4C with an input of 0.98v from cap 1h1 390 2.5v however the output from the R36W 4C was very inconsistent it would jump from anywhere 2.0v to .01v I'm thinking this is likely the cause of my issues, but just wanting form further feedback.

    There was one other thing that struck me as a little off. Part PQ52 all the legs besides one read 19.40 one of the legs reads 8.40 which struck me as off, but it may just be how that part works.

    Any help would be greatly appreciated.
    Last edited by spokenlastchance; 04-23-2014, 04:00 AM.

    #2
    Re: Intermittent power PEW71 LA-5894P Mobo Acer 5742G

    Should I link a schematic would that help?

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      #3
      Re: Intermittent power PEW71 LA-5894P Mobo Acer 5742G

      Originally posted by spokenlastchance View Post
      I tested the device on another charger inside an electronic store making sure it was within the specific standards. This also didn't work, but we got flickering as we put the DC jack in so I tired replacing the DC jack, and It's still doing the same thing.
      You got flickering on the led of the power supply adaptor (charger)? This points to a short.
      What is the voltage on PQ52 pins when it doesn't start?

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        #4
        Re: Intermittent power PEW71 LA-5894P Mobo Acer 5742G

        PQ52 Is the one I noticed had a weird voltage on one of the pins. All of them have 19.5v besides one leg which has 8.3v This stays constant no matter on or off.

        The flickering went away though it no longer does that it's either on or off I think that I just had the connector lose.

        I marked on the picture the pin that's having the issues, and also indicated the RC36W that is also having issues.

        The schematic was for the LA-5893P I couldn't find the LA-5894P with searching figured it was close enough.

        I also could not find a boardview diagram for this board which makes pin hunting pretty hard if someone could supply that it would be fantastic.
        Attached Files

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          #5
          Re: Intermittent power PEW71 LA-5894P Mobo Acer 5742G

          You probably do not need a boardview (I do not say it won't help you). Pin numbering is clearly marked on the board.
          8.3v on pin 4 is what you want on an that p-channel fet. I imagine the voltage on all pins of PQ52 stay the same after it shuts down and won't accept to start again.
          Have you checked the temperatures with a software like speedfan?

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            #6
            Re: Intermittent power PEW71 LA-5894P Mobo Acer 5742G

            I can hook it up again the bios on this thing sucks you cannot see anything in the stock one.

            The thing I find so weird about it though is I can have the computer entirely off for and just charging the battery, and it will just stop taking charge after about 2 hours.

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              #7
              Re: Intermittent power PEW71 LA-5894P Mobo Acer 5742G

              is it a genuine charger? i have a acer i was given it would either charge the battery only or turn the laptop on with the battery removed after a lot of searching i have found i need a 19 volt 7.1 amp charger the one i got given was only about 4 amps so could not power the battery charging and power the laptop circuits the same time this would also run for a few minutes at times worth a check i guess.

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                #8
                Re: Intermittent power PEW71 LA-5894P Mobo Acer 5742G

                Nope it's the stock charger that was one of the first things I tested. I first thought it was either the charger or the DC port. So I changed out the DC port, and then I took it up to bestbuy and found the same acer charger, and it was still doing the same thing.

                I'm 90% sure there is something wrong in the power circuit in relation to DC power being transferred to the main power, and battery that I think is overheating. Because like I said it will power on and charge for about 2 hours, and then it will no longer accept power from the DC unless I let it sit for about 12 hours. It will run down the rest of the battery charge once the DC power goes out and still works fine. If I remove the battery it will no power on. The computer runs fine directly though the battery. I've considered taking out the cells and wiring it up, but that is just a ton of work.

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