MacBook Pro A1502 2013-2014 USB ports not detecting drives repair

Problem description
When the A1502 MacBook Pro is not detecting connected USB devices.

Symptoms

 * Unable to detect USB devices.

Solution
For left port on logic board check for 5 V at L4605. If low or non existent check for PP5V_S4 at pins 2 and 3 of U4600. If that VIN is OK check for USB_PWR_EN at pin 4. If that is low try removing U4600 and rechecking USB_PWR_EN. If it comes back up to ≈3.3 V then replace U4600 and recheck for 5 V at L4605. This obviously doesn't cover all possible scenarios but it is one.