Pressed power button, unit powers off after 3 seconds.

Bypassed protection mode by holding "Effect" & "Night" buttons while
pressing power button.
Unit displayed the code "PRD PRT 210"

Manual states as follows....

When there is a history of protection function due to abnormal DC
output

PRD PRT:xxx (xxx AD value when the protection function is working)

Cause: DC output of the power amplifier is abnormal.

Supplementary information:
The protection function worked due to a DC voltage appearing at the
speaker terminal.
A cause could be a defect in the amplifier.
If the power is turned on with the abnormality unsolved, the
protection function works in about 3 seconds to turn
off the power.

Ideas where to start? LOL.... DC voltage appearing at the speaker
terminal? None showed
up with a DVM