PISMO squealing: I give up.

Discussion in 'MacBook Pro' started by kirk wilson, Oct 21, 2008.

  1. kirk wilson macrumors member

    May 18, 2008

    I have an old PISMO, it squeals all the time, like a photographer's flash
    unit charging up. I have replaced:

    the sound card
    the PMU logic/battery board
    the entire motherboard (just today)

    What else is there to replace? There is no other circuitry. It's not the fan.
    It's not coming from the speakers. It's a diode or capacitor, or something in a circuit board.

    Is it the 400 mhz processor? I'd replace that too, if I could get a bigger one.
    But at 400 mhz, why bother? (the aftermarket upgrades cost $300)

    It only squeals when plugged in; I unplug it for some peace and quiet and then plug it back in to recharge the battery.

    I was sure, after today's replacement of the motherboard, that the problem would finally go away. That's what you get for being confident!

    The PRAM battery hasn't been replaced, but then,
    a battery can't squeal. Can it?

    I know all of you have million-dollar MacBook Air notebooks, but does anyone out there have an older PISMO which makes loud squealing noises?

    It's.. going.. out the window, soon.. very soon..


  2. 840quadra Moderator


    Staff Member

    Feb 1, 2005
    Twin Cities Minnesota
    LCD screen? Something to do with the backlight transformer or otherwise?

    Not sure otherwise. Sorry to hear you are having problems with that system. Really miss that series myself!

  3. Kane.Elson macrumors regular

    Jul 27, 2006
    Sure it's not the AC adaptor? If you have replaced all the circuitry I can't really think of anything else.
  4. kirk wilson thread starter macrumors member

    May 18, 2008
    ok, I don't really give up

    To answer the last question, yes, I have two different AC chargers here
    for the Pismo, one is Apple-made, and the other is Apple Approved (whatever the hell that means. I think it means it costs more.)

    It hit me last night-- Change the Inverter!

    It's the pencil-sized circuit board at the base of the screen, and to my knowledge, an Inverter is something you use to
    convert AC voltage to DC Voltage.. like in a car or a camper or for the
    solar panels on your roof. This Pismo screams when the AC plugged in,
    but not when it is on DC (battery) power. That's it!!

    But- I wake up this morninng and realize that this inverter board is
    dedicated to the display screen, and the screen seems to be perfect.

    Is that right? Or is there another Inverter somewhere in the Pismo?

    (the PISMO takes 24 volts AC in, although the battery is of course, DC).

    So, I'll order another Inverter board, they're only about $8 new, but honestly I would guess that the loud squeal noise comes from something
    too big to be on that tiny pencil-sized board.
    I'm thinking a big diode or capacitor. But I can't view them without dismantling the laptop (or risking program destruction when I take off the keyboard while it's powered on...)

    Can I take it apart while it's powered on?

    I alomst wish MacBook Pros were starting to do this; that way there would be a national outcry and a Congressional inquiry! This is becoming the
    Corvair of computers. (you know I'd buy a Corvair in a heartbeat if I had the dough..)

    Somewhere, out there is a true electronics nerd who will say "Uh.. that squealing is obviously caused by the _____ connected to the _____,
    you moron! What were you, Home-schooled??"

    Oh well, until next time..

  5. risenphoenixkai macrumors regular

    Oct 14, 2008
    It might be the battery that's squealing, or the inverter that feeds it.

    I know that every time I plug in my 5th gen iPod to charge it, I can hear a faint but easily discernible high-pitched squeal from it.

    Try running your Pismo straight off the wall outlet, with no battery in the left bay at all.
  6. duffyanneal macrumors 6502a


    Feb 5, 2008
    There was a known issue with Pismo's inverter boards. I had to have mine replaced shortly after I bought it. If I recall correctly it didn't squeal at full brightness, but the lower the brightness the louder it became. The board is located at the bottom of the display behind the plastic trim panel. Listen for the noise there to see if that is your problem.
  7. kirk wilson thread starter macrumors member

    May 18, 2008
    thanks, it's coming from the battery/logic board

    Like I thought, it's coming from the middle of the laptop, loud enough to
    drive someone insane. I already changed the PMU/Battery logic board, but that
    sounds like where it's coming from.

    (it's not in the screen inverter; I disconnected it
    while the pismo was charging (but off), and it was still squealing.

    I have pulled the battery while the squeal noise is present and the noise drops to a lower tone, but doesn't go away. So it's no use to remove the battery
    except that the squeal is lower and more erratic sounding.

    So I guess I could get ANOTHER PMU/battery board; maybe the one I was sold was bad also.

    I just want to fix the thing.

  8. ickystay macrumors regular

    Sep 3, 2006
    I use my pismo almost every day and am quite fond of it.

    Weird, I never really thought about why photo flashes make that noise. I think they are basically a battery that charges a high value electrolytic cap to a point where it's discharge is enough volts to fire a zenon tube.

    Is the sound from the cap, or from the circuitry charging the cap?

    Have you tried removing the battery and disconnecting the pram battery at the same time? In that state, nothing to charge/nothing charging.

    I know the "It's going out the window!" feeling.

    Good luck!
  9. Fox McCloud macrumors newbie

    Aug 6, 2009
    The Easy Pismo Fix

    Considering you've probably been inside the Pismo you shouldn't have any trouble with this. Remove the keyboard as well as the hinge cover with the power button. Next you'll see a slim board connecting the screen to the unit. Use a glue gun to glue it in place so it's resting firmly against the case. And thats it, it worked for me, hopefully you'll have the same success.
  10. Macdctr macrumors 6502

    Nov 25, 2009
    Possible problem is the AC/DC converter board

    I had a high pitched noise as well in my Pismo and when I changed out the AC/DC converter board (aka. Sound Card) I no longer had that high pitched noise. The Sound card is the board where the Power adapter connects to your Pismo. It's the weak point for the Pismos and they fail on occasion. I have gotten a few from ebay just in case I have to replace this board again.:apple:

    Here is a good link to repair the Pismo. I used this until I became quite familiar with the internals of my Pismo. It has alot of great pics to help you along...hope this helps :apple:


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