The issue was created by the recap since it worked before. There has to be something done that either is preventing signal from passing or cut off power to a section. If you look in the schematic there are voltages which can be used as test points. It may show them on one channel and not the other but obviously you want to test both sides. A meter is going to be your best friend in finding this problem. The power supply for example at pins 13+14 have voltages that should measure 13.5vDC and 35.6vDC. I would start with the power supply and work your way through the signal chain if you find nothing there. Put your meter in vDC, ground the negative probe; I like using an alligator clip to the chassis. Wrap the positive probe with electrical tape except for the very tip to protect it when (not if) you slip and touch another point of the board. Receiver powered up do some probing using those test voltages in the schematic. With both channels out there is a better chance something is not getting proper power then both signal paths are blocked. Were any transistors replaced when you recapped the receiver? Incorrect pin out installation is common when substituting modern transistors for vintage.