Focusrite Scarlett 18i20 gen 2 knocked off USB B port and inductor identification

[djowel]

Hi All,
I have a Focusrite Scarlett 18i20 gen 2 interface on my bench with a knocked loose USB B port.

Replacing it isnt so much the issue, but did also knocked of L11 of the board, which went AWOL.
The inductor sits in path between the port and the XMOS XFR001C DAC chip.
I'm guessing this is a common mode choke, but could be totally wrong.

Does anyone can give me a clue on what type or value inductor I need to replace?
I cant find any datasheets or schematics on this type of xmos chip. And of course no data from Focusrite.

I've seen @Khron blog online where he repaired similar interfaces. Maybe he can shed some enlightment upon this mystery.

Anyway thanks in advance, all help is welcome!

cheers,

Joel

Photo of an undamaged 18i20 PCB with said inductor L11

 

[Khron]

Worst-worst case, you could replace that with a pair of thin copper wire strands, at least for testing, and/or if you don't want to wait for delivery of a single correct component.

That should indeed be a common-mode choke, roughly 0805-sized or so (not sure what the stndard footprints for those might be).

 

[djowel]

Thank you for replying @Khron. I can get my hands on a undamaged 18i20. How can I measure the inductor to find out which values look for? Can I use a LCR and DMM for this? And which criteria should I be looking for?

If I go the jumper route, what is the risk I might be taking?

 

[ccaudle]

If I go the jumper route, what is the risk I might be taking?

Check to see if there is a ground terminal underneath the part. If there is, the part might have integrated ESD filtering. If not then it is probably just for EMI mitigation, so the "risk" is that you would have higher than designed common mode noise coming out of the USB port.

When I go to DigiKey and look up common mode chokes and inductors, there are some product lines which have "USB" in the name. In fact one series name is "0805USB," that would be as good a place as any to start looking for a replacement. First make sure of the footprint dimensions, then start looking for something in that package that the vendor recommends as good for USB 2 applications. Should not be too critical.

 

[djowel]

Thank you @ccaudle for your input. I'm putting the pcb under the microscope later this evening, to see how the inductor is connected and to verify package size. But this info certainly gets me a step closer to fixing the problem.

I've come so far to find coilcraft cmc in 0805 package for usb2.0 on mouser myself. But still 8 versions (dif. values nH and DCR) to choose from.

 

[djowel]

Okay, size seems to be 0805.

But it seems inductor is connected between D- (Pin 2) And D+ (pin 3). No ground connection.

So, I should be safe to just connect the pads and test?

 

[ccaudle]

I should be safe to just connect the pads and test?

Yes, you can just jumper across if you want to test the USB function.

 

[djowel]

Hmm okay thnx. So no permanent solutions then. I will see what measuring inductance with LRC meter will give me on an undamaged 18i20.

Is it just a matter of reading inductance with LCR on both sides of the inductor? And DCR with DMM? Or am I missing something to identify the correct replacement part?

 

[ccaudle]

So no permanent solutions then

You could leave it that way permanently if you want, if you are willing to accept that it may have higher EMI emissions than before.

 

[Khron]

You could leave it that way permanently if you want, if you are willing to accept that it may have higher EMI emissions than before.

... Which may or may not have any observable effects anyway

 

[djowel]

Okay, great info. Thanks alot for your insights!