Hi,I've newly assembled c4s board.4 leds are ok,all tubes are ok.Voltage checks are ok except terminal 2 and 14.they are a little lower than range.The right channel sound ok.There is also sound in left channel but there are some cracks,pops in left channel.I dont use potentiometer now,i am waiting for alps potentiometer to arrive.Where should I check for this left channel problem? Thanks again.