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Apple iMac 21.5" A1418 820-3302A Blown Caps

Discussion in 'Troubleshooting and Repair' started by Sniper Schematics, Apr 25, 2017.

  1. Sniper Schematics

    Sniper Schematics

    6
    0
    Apr 25, 2017
    Hello everyone!

    So i have this imac 21.5" that appears to have water damage. There is a dry pattern of water on the fan plastic, its kind of hard to tell but from seeing water damage repairs for years you kind of pick up the patterns. So the unit turns on and you can barely see the image because there is no backlight. I did some continuity testing on these nasty looking capacitors and two of them were a no go. I touched them with a pair of tweezers and they immediately fell off. I cleaned up the area with my soldering iron and this is the end result. Honestly I dont know what sort of damage im looking at. As tittle states this is a iMac model number A1418 and the board number is 820-3302A
     

    Attached Files:

  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,178
    2,690
    Jan 21, 2010
    If you still have the capacitors and know where they went, measure their capacitance. Otherwise it will be really hard to determine the appropriate values. If you're lucky all of them are the same value, but since these capacitors are not marked...

    The photos are sufficiently blurry that they're not too useful. May I suggest you go here for some tips.
     
  3. Sniper Schematics

    Sniper Schematics

    6
    0
    Apr 25, 2017
    You got it. I will take some pictures tomorrow and hopefully we get a better result.
     
  4. 73's de Edd

    73's de Edd

    2,678
    1,085
    Aug 21, 2015
    Sir Sniper . . . . .

    What board are we looking at, as I have no other recognizable “ Landmark” components to reference ?

    Pull out your ohmmeter and confirm its lowest ohms displays readout of a shorted probes connection and then move on to the 6 colored lines that I have laid out. Expecting each colored line set to be interconnected.

    The WHITE star is a ground plane, use a probe to break thru its resist layer to get good ohmmic contact and then find yourself a solder connection that connects to it, and then use THAT soft soldered connection as your probes new ground reference point and check to the colored stripes to see how many are being grounded also. While at it, also check out RED star, down all by himself to see if one of his leads is being grounded.

    Consider these block monolithic ceramic capacitors, being used for decoupling:

    Looking at I-mac schematics they use a ton of .1ufd, of the ~ size profile shown within the Yellow rectangle.

    A considerable amount of 1 ufd 6.3VDC which I suspect your markups units to be

    And a decent amount of 2.2 ufd 6.3VDC units are used.

    I am hoping that you have capacitance measuring instrumentation.

    Just measure and see if that sole survivor . . . . . PINK-GREEN unit is reading ~1 ufd.

    Then check PURPLE-YELLOW . . . . .RED- BLUE to see if those sets read ~3 ufd

    And old RED star down there, also being a 1 ufd unit.

    Is our copper contactor, that is sticking up, being a grounded connection ?


    Photo markup:


    [​IMG]


    http://i.imgur.com/XcD7LJz.jpg




    73’s de Edd
     
    Last edited by a moderator: Apr 28, 2017
    Warg6 likes this.
  5. Sniper Schematics

    Sniper Schematics

    6
    0
    Apr 25, 2017
    Sir 73's thank you very much for your response. I will go through your information shortly.

    I wanted to provide some better images. I also got the schematics for this board and highlighted the values of one of the missing caps.
    The exposed copper is exposed because the PCB that laid on it was burnt and brittle.

    20170425_104329.jpg 20170425_104329.jpg 20170425_104309.jpg 20170425_104259.jpg
     
  6. Sniper Schematics

    Sniper Schematics

    6
    0
    Apr 25, 2017
    I tested the caps and they read 2.2 which is what the schematics show. 2.2uf 10% 100V , and this is for backlight. The copper plaint sticking up was what was left over after some cleaning of the area, the pcb was totally crunchy. I took this board and told me all of these components are shorted. he really does not dabble in computer but has been repairing TVs for over 40 yeras. Her said pull the board out and lets look at the underside. Just wanted to give you guys an update.

    Also I apologize in advanced if im not providing certain needed information, Im new into board level repairs, and I have a course coming up in 2 weeks which will significantly improve my knowledge.
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,178
    2,690
    Jan 21, 2010
    If the board if charred, it will be very difficult to repair. I would suggest that for a multi layer board repair is not viable.
     
  8. Sniper Schematics

    Sniper Schematics

    6
    0
    Apr 25, 2017
    I can see that being so. Like I mentioned, the caps fell right off to the touch and ass you can see the pads are all exposed and the one orange area was raised and charred. These capacitors power the back light which I believe uses like 50V to power on, dont quote me on that dont have schematics in front of me.

    Thank you guys for your help.
     
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