As I remember in the D90 thread, this is not the first DAC you have had these issues with, 99.9% of users do not have this issue which likely points to some sort of compatibility issue.
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Gippy
Hi ostewart,
I mentioned that the iFi Micro iDSD Black Label also has drivers that put the DAC to sleep after a few seconds of no USB audio signal. This is the default behavior because the MiDSD BL can be operated by its battery, and not having this would allow the MiDSD BL to drain its entire battery. However, iFi has provided drivers that disable sleep mode, which I downloaded and used successfully. The Topping D90, being a completely AC powered desktop unit, has no excuse for this sleep behavior.
Also, please don't throw around statements like "99.9% of users do not have this issue" without backing it up with real data. For this to be true, Topping would've had to have sold at least 2000 units in 4 months, which is very doubtful because this is Topping's $700 flagship, not their $90 D10. As you can see, The Dude Abides also had issues with his D90.
I mentioned that the iFi Micro iDSD Black Label also has drivers that put the DAC to sleep after a few seconds of no USB audio signal. This is the default behavior because the MiDSD BL can be operated by its battery, and not having this would allow the MiDSD BL to drain its entire battery. However, iFi has provided drivers that disable sleep mode, which I downloaded and used successfully. The Topping D90, being a completely AC powered desktop unit, has no excuse for this sleep behavior.
Also, please don't throw around statements like "99.9% of users do not have this issue" without backing it up with real data. For this to be true, Topping would've had to have sold at least 2000 units in 4 months, which is very doubtful because this is Topping's $700 flagship, not their $90 D10. As you can see, The Dude Abides also had issues with his D90.
trellus
Blech, thanks for the heads up, I now have zero interest in this persnickety, overpriced hodge-podge. 
If you are certain your usb has blown on the D90 I would try to have it assessed by local technician. Even a PC repair outlet may be worth a shot if it is something minor. Air mail is one of the things with the Topping warranty plus the additional import tax for the return. It would really be worth your while to hear this at its best
You might contact a young man on the Audio Science Review forum called JohnYang 1997. He is an electronics student in China and quite a wizard with Topping design. Perhaps if you were to p.m. him it might give you some hope and explain your options.
Good Luck, hope you can sort it.