A possible $3 brute-force hack/"fix" that's been working for a while.
OK, so I also registered to post about this issue. Thanks to others for posting the temporary workaround (heat) to get these problem C-Media USB 2.0 audio chips recognized again.
I acquired a Schiit Modi 2 with this very problem that was waaayyy out of warranty. Not recognized until I heat up the C-Media chip a couple mins w/a hair dryer. Most certainly not a "solution" because every time you shut down the computer or DAC you've got to unscrew lid, apply heat, then Yay! DAC is recognized (again).
BTW this is not limited to Schiit DACs using these C-Media USB audio chips (e.g. CM6631A)... Other DACs using it can experience this problem, e.g.
some Emotiva units - "
I can tell you that failure of the C-Media chip is one of the more common faults we see in the DC-1. It doesn't go by batches or anything like that - that particular chip just seems to be more prone to failure than many other components."
Anyway, I've built several amps & headamps but never worked w/SMD. I could certainly order a new C-Media chip (~ $13 shipped?), buy a hot air re-work station (decent ones $50?) OR ChipQuick SMD1 removal kit ($16), plus a bevel solder tip ($12) and give it a go. And maybe I will if/when this $3 hack stops working...
For now I'm using this $3, possibly temporary but working for a while now, solution - a $3 shipped eBay Chinese "5.5*4CM 5V Carbon Fiber Heating Pad Hand Warmer USB" small USB heating pad. So far this had been "fixing" the problem for over a week now. I power the double-faced tape-attached heater pad for < 2 mins (through phone charger) and then
bing! the Modi DAC is recognized, disconnect the USB warmer, and the DAC works for the whole day (until I shutdown).
Steps I used:
1 - Confirmed USB not recognized problem was the frigging C-Media USB audio chip... A hair dryer on low applied to it for a minute or two made it magically recognized.
2 - Ordered a USB heat pad like referenced above. Waited a couple weeks for it to arrive. Tested it by plugging into USB phone charger (not your PC/Mac), it got warm.
3 - Used strong double-faced tape, the type with a blue peel layer on the outside, to attach heat pad to frigging C-Media USB audio chip.
4 - Passed its wire out the back & was able to somewhat tighten the Modi 2 DAC's lid screws.
5 - For me, I power the heat pad for ~ 2 mins from an iPhone charger and voila! - the Modi is recognized & works well for the day.
Photos or it didn't happen:
the bugger:
the smallest USB warmer I could find... Is actually smaller than it looks here:
USB warmer attached, its USB wire out middle-back & screws tightened lightly:
Booted Mac not seeing DAC yet...
After 2 mins powering heater:
Unplug USB heater, DAC working well until next reboot.
Wild that a "fix" they use for diesel engines, block heaters, would have application for an IC