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Processeur dual-core Intel Core i5 à 2,5 GHz (Turbo Boost jusqu'à 3,1 GHz) avec 3 Mo de cache L3 partagé.

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Right side I/O board preventing start up

Several weeks ago, I had to change the battery for a second time in my late 2012 i7 Macbook Pro Retina (A1425). After fitting the new battery and hitting the start button, the Magsafe connector lit green, then briefly orange before dimming and dying completely and the computer showed no sign of life. Measurement of the voltages on U700 showed that the chip had become damaged and effort to replace the chip resulted in a few of the board contacts lifting under the heat required to desolder. So, I bought a replacement second hand logic board. Upon start up, all appeared fine except that I had forgotten to couple the 6 wire plug connected to the right side I/O board to the logic board, hence no wifi device was detected. After connecting the plug, the computer would no longer start: no fans, no chime, black screen and no key combinations (SMC reset, PRAM reset, Shift, Option R, Command D, etc. made any difference. I have since discovered that the computer can be started if the right side I/O board is again disconnected and an SMC reset is performed followed by a hard reset (connect the Magsafe while the start button is pressed). I do not have the circuit diagram for the I/O board, so cannot check the voltages that should be present on the 6-wires that connect to the mother board. Some of the wires show continuity with each other, which may indicate that they are shorted. If anybody has an idea of what could have gone wrong with the I/O board or can give me the voltages that should be present on the 6 wires together with their continuities I would be most grateful for the help.

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@flannelist I suspect the capacitor next to the incoming PP5V_S4 is faulty but haven't yet removed it from the board. Would you have an idea of its size because I cannot find a circuit diagram for the I/O board (820-3199A) either?[image|3080116]


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Some of those may show continuity, depending on which you're looking at. You're checking on the Logic board side, correct? Rather than the I/O board side. Here's the pinouts for the logic board side. Pics for reference.

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From top to bottom:

  1. Ground
  2. Ground
  3. 1.5V (I assume since that line is called PP1V5_S0)
  4. 5V (This is PP5V_S4)
  5. 3.3V (PP3V3_S3)
  6. 3.3V (PP3V3_WLAN)

You should definitely get continuity between the top 2. And possibly also for the bottom 2. But I'm not 100% sure on that because they connect via an IC so could go either way.

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Hi Alisha,

Thank you for the rapid reply.

I am measuring continuity of the wires attached to the I/O board, not the logic board, as the latter seems to be fine and I read that battery changes can cause problems with the I/O card. According to your wire number order, I have continuity between wires 1, 2 and 4.


So, PP5V_S4 is shorted to ground.


@johnchisholm I forgot those wires are soldered directly to the board on the IO board side, so still accurate. I just meant in order by the board side connector. But knowing no short on the logic board helps too. Definitely sounds like a 5 Volt short. I can't find schematics or boardview on that specific IO board. But even knowing you have a short might help. because that's at least something.

It's a pretty small board. I would probe around and see if you can figure out what other components might be on that line. I can probably compare and contrast if need be because I don't expect all of the circuitry will be totally unique to that board either. I have a few IO board for other models around, just not that one.


@flannelist I suspect the capacitor closest to the incoming PP5V_S4 wire is faulty but haven't yet removed it from the board. Would you have an idea of its size because I cannot find a circuit diagram for the I/O board (820-3199A) either? Unfortunately, I haven't figured out how to add an image to this comment to identify the suspect cap!


@vagus I meant to respond a couple of days ago (my apologies). You can [Ajout d'images à une question existante|edit your original post to add in some images.


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John Chisholm sera éternellement reconnaissant.
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