I own such a USB DAC and there was not a single problem in 2 years - I took it on a journey for few days and when I returned I realized it is no longer working ok. One chanel is dead, another chanel is very noisy - you can hear the signal but noise is much louder than signal itself.
Checked inside for broken parts suspicous soldering points etc. seems to be ok, all capacitors are fine, V supply is ok on each chip, ground seems to be connected everywhere - as long as my multimeter tells the truth.
I checked this dac on several computers on usb input and behaves the same - amp and headphones are ok - working perfectly with another DAC.
Can you suggest where to look for malfuntion? What to check? What tests to make?
Thanks for any suggestions :)