Logic Board Repairs Repairs

Dead Macbook Pro Logic Board Short on PP5V_S3

Macbook Pro Logic board repair can be a difficult task when no corrosion is found on the motherboard fortunately, in this case there was some corrosion found

Today we had a Macbook Pro A1398, not turning on. In this post I’m going to detail the repair and its symptoms in the hope that it will help someone in the future.

Customer said the Macbook Pro just stopped working one day. It would not respond to power button presses or an SMC reset. However, the Magsafe charging light was on and charging the battery which is a good sign.
The first thing to do is disconnect everything external to the motherboard / logic board including keyboard, trackpad, daughter boards, battery etc. The power button is a part of keyboard so if you have a problem with the keyboard, it won’t power on.

With everything disconnected including the battery, the Macbook should turn itself on when the Magsafe power supply in attempted which it didn’t.
Upon hooking it up to a DC power supply, we found it was taking 10ma and indeed not responding to power button presses. Tried an SMC reset while on DC power supply and it would jump from 70ma to 80ma and back to 10ma which tells us that the power button seems to be working.

We started by removing the back cover to do a visual inspection on the board and found no signs of water damage or corrosion. Checked PP3V42_G3H which had 12.5v as expected because this line is required to get a light on the charger. No PP3V42_G3H means no light on the charger.

The next step was to remove the board in the case in order to check the other side of the board and only to find no signs of water damage under the keyboard. upon closer inspection of the motherboard, we spotted two teeny tiny dots of corrosion, one spot by the SMC and one by the PP5V_S3 line. The spots were microscopic and could only be seen under 4x magnification. Checked the schematic and boardview for 820-3787-A for these locations which had a couple capacitors connected to ground so thought that would be a good place to start.
On the multimeter, the capacitors by the SMC measured ok, not shorted to ground but on the PP5V_S3, it was almost short. This could be our problem. Started up the hot air and replaced all capacitors near the corrosion of the PP5V_S3 and our short was gone!

We then plugged in the fans and attached the magsafe power supply. We had fan spin! Since the capacitors by the SMC were corroded, we went ahead and replaced them even though they weren’t shorted just to avoid future issues.
And that’s it, just reassembled the Macbook Pro and checked for proper operation.

Not every no power issue is the same so if you have a Macbook Pro that is not powering on, why not get Magic Mike a call on (03) 929-2837 and ask for a quote today.