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What’s wrong with this MacBook?

This customer sent in their MacBook Pro to our store in New York City for our logic board repair service because the USB ports weren’t working. Before starting the repair, we needed to figure out exactly what was wrong with the machine. We started off by booting the machine into the boot options menu and plugging an external drive into each port to see if it was recognized. We discovered that neither port recognized the drive, so both USB ports were totally dead.

How do we fix this issue?

Diagnosing the board

We start off by checking the schematic diagram for this 820-2936 MacBook Pro to see how the USB ports work. Conveniently located on page 2 of the schematic is a block diagram that shows the flow of the USB circuits. Here we see that each USB port is controlled by a separate hub, with both hubs having a connection to the PCH. This means a few things. Because it is very unlikely that both USB hubs have failed simultaneously, something that both ports have in common must have failed. This can be one of a few things, such as a component responsible for powering both USB hubs or the PCH itself, which is a difficult repair to perform due to the complexity of the chip.

Next, we have to find the components on the board that we saw on the PDF schematic. For this, we check the boardview for this MacBook. This will allow us to see where those individual components are on the board itself. We locate the two USB ports on the boardview and find that both ports are connected to U4600. On the PDF schematic, we see that U4600 is labeled as “USB Port Power Switch.” U4600 has one enable line, one input line(PP5v_S3), and 2 output lines (PP5V_S3_RTUSB_A_ILIM and PP5V_S3_RTUSB_B_ILIM). Each of those lines goes to one of the two USB ports. This means that U4600 is something both ports have in common that can cause neither of them to work if it isn’t working properly.

The next step is to begin measuring voltages to see what lines are present and what lines are not present. We locate U4600 on our board under the microscope, and use a multimeter to measure voltages. First we measure the power lines for each USB port. Both ports are measuring 0.04V, which means neither port is getting power. This tells us that the issue could be one of a few things: Either the chip is dead, the USB power lines are shorted to ground, or the input or enable line for U4600 is missing.

Now, we check the pins on U4600. We find that both the input and the enable lines are present. This leads us to conclude that either the chip is bad, or the output is shorted to ground. Resistance mode on the multimeter tells us that both lines are shorted to ground. Since both lines are on one chip and both lines are shorted to ground, the likely culprit in this situation is U4600, the chip itself.

Repairing the Board

With our Quick 861DW Hot Air station and Amtech Flux, both available on store.rossmanngroup.com, we remove the chip. After removing the chip, the short is gone. After replacing the chip, one USB port functions again, but not the other port. This means that something else on the board related to that one USB port is causing it not to work.

After some more detective work, we discovered that the port is now getting power but not turning on. This means that the port itself is bad, or another component is bad going to the port. U4650, an SMC debug chip going to the port, or L4600, which goes from U4650 to the port are possibly causing this, so we replace them both to rule them out. Luckily, that solved our issue, and this MacBook now has working USB ports again, thanks to our great team of technicians at our MacBook Repair location in NYC.

I can’t fix this myself. How do I get it fixed?

Rossmann Repair Group offers MacBook Logic Board Repair in New York City. Our MacBook Repair is not limited to NYC though, we accept mail-in repairs from virtually anywhere! Visit https://sendyourmacbook.com to start your MacBook repair.