Then remove the volume knob, try to rotary the inside volume knob and tell us if the unit volume can be adjusted.
If not, it's possible the volume knob part on the TFT board is broken.
About the android 5.1, the factory told us that the android 5.1 firmware was not available on android 4.4 unit now, and the result we tested also show the android 4.4 unit could not find the 5.1 upgrade file.
About the sub output adjustment suggestion, we will feedback to factory and try to release the new unit which support this function.
RegardsStatistics: Posted by Jammy — Thu Jun 16, 2016 7:38 am
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