When replaced, measure various parameters vs the not failed/repaired other negative section too. Of course -Vo first, but also mV drop across the 1Ω resistors (1mV=1mA) to see if all the led-bars are driven by the same mA CCS more or less, Vbe of the BJT transistors to see if all are still on, compare some spot voltages vs ground between the sections etc.
I hope you did not compromise the TKD when you tried it on a loudspeaker output with a speaker as load. Do you have a cheap spare log pot to wire and compare? Before doing that connect RCA ground pins together. First the input ones, if nothing changes connect the output RCA ground pins together, if nothing changes again, from their common run a link to the input RCAs ground pins. All that locally on the RCAs at the back panel plane.
13.886-13.746=0.14V difference. Where's the 0.5V difference?
By the way, Vo=Dref-Vbe(BC5xx) in this circuit design. Your figures are compliant.
Indeed, 0.14 V difference.
0.5V was before the led-bars replacement, I'm sorry for the confusion between the measurements.