MacBook Pro 2012 USB Ports not working correctly.

The USB ports on my Mid 2012 Macbook Pro 15” i7 have stopped working correctly.

If I plug my external USB hard drive in, this still works and I can back up etc. If I plug my brand new iPhone 11 in nothing. If I plug my audio interface in it will work then cut out then work then cut out, then stop. Same with my USB Keybaord (musical keyboard). USB memory sticks don't appear to work. Connecting using a mains powered hub, makes no difference.

I think the logic board is 820-3330-B.

I have done some digging and I have 5V at both USB ports which I can trace back through L4605 & L4705 chokes to the Power controller IC U4600 (TPS2561). I have checked around U4600 as well and can confirm 5V on pins 2 & 3 and on pins 4&5. So I am assuming all is well with the power side of things.

Next up looking at the schematic I can’t see much else that could be at fault other then D4600 & L4600 (and D4700 & L4700 on the other port). With my meter I can’t measure anything like 90 Ohms through the chokes (L4600 & L4700) - my readings range from best of 200 Ohms to open circuit. I can’t make any meaningful readings with the Diodes.

So I am thinking I may as well change these components and see what happens. But as I do not have the necessary soldering equipment I need to take it to a colleague for this work, which will not happen for a couple of weeks. This has given me time to think... Why is this an intermittent fault and why do some devices work? Would be interested in other people’s thoughts on this...

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