Focusrite Scarlett 18i8 2nd Gen USB not getting recognized

[sadaghian]

I have this 18i8 from late 2018 that works standalone as it is configured right (as a mic preamp, 48v and outputs work) now but does not get recognized by computers, the USB LED on the interface itself also doesn't light up, was wondering if it is a known issue and if anyone has schematics for this device.
Thanks!

 

[Khron]

No schematics, but just the other day I posted a teardown on my blog. The usefulness of that in your case is debatable though.

Assuming the connector itself is ok, and the common-mode choke that's on the pair of data lines is ok (L25, should show continuity), you might end up needing to contact Focusrite's spares department and see if they'll sell you (or at least identify) the model of the Xmos controller used in this. Hooray for total integration.....

 

[chilidawg]

Aside from that maybe check the low voltage supplies for the XMOS chip and the flash memory next to it (measure at the ceramic caps)

Not sure what the low voltage values are, maybe the usual 5V, 3.3V, 2.5V, 1.8V or something. I guess Khron can tell you more because he owns the same unit?

I noticed there's also a test point on the board to check if 1V is present or not.

 

[Khron]

1v rail powers the Xmos processor core; other than that, there's a 3.3v (buck converter) for the digital stuff, 5v (7805) for likely only the converters, +/-6.9v for the analog stuff, and the 48v phantom power.

If all else works apart from the USB, that's most likely where the issue lies.

 

[usbdevice]

.... Assuming the connector itself is ok.....

This is the first thing I would check. I have a Scarlett 2i4 that wasn't recognized by any computer. It turned out that one of the contacts inside the USB Type B socket on the interface had been bent/pushed back by the cable plug at one point. Replacing the connector solved the problem.
Check the solder joints of the USB connector too.

 

[sadaghian]

thank you guys, i will try to try your suggestions this weekend and report back

 

[NoisyIndividual]

I find 95% of no USB recognition is cured by replacing the socket, but I have replaced a few interface chips too.
A couple of times the series chokes Khron mentioned were faulty or detached.
I've always found it quite easy to find the input pins on the IC the chokes go to, plug a USB cable into the socket, and meter for continuity end to end.

 

[Khron]

One unfortunate thing about these gen2 units is that the Xmos chip incorporates the USB chip functions, so if that kicks the bucket, the main processor needs replacing altogether. Gen1's still had SMSC interface chips, but oh well...

 

[NoisyIndividual]

It's way more common for FireWire chips to get fried, since it's possible, particularly with a worn socket, to either put the plug in upside down, or inadvertently connect the wrong connectors at the wrong time, destroying the chip instantly.
USB seems far more robust in this respect.

 

[NoisyIndividual]

I believe the USB protocol requires all equipment to be able to withstand any pin connected to any other pin indefinitely without damage to anything.
Pity FireWire didn't adopt that.