MK 136 low volume output on the right channel only

Kits Audio Hi Fi Projects
1

1st question) Hey wondering if someone could tell me where to start looking for the reason of a low audio output on the right channel only. Approximately 1/2 the volume of the left.

2nd) Regarding the R8 and R7 resistors, which one is the right channel and which one is the left?

Cheers

2

R8 is connector to the tip of the 3.5mm stereo jack, so this is the left channel.
Volume difference is most likely caused by soldering/assembly problem or wrong resistor value, please check.