Sounds like you had a loose connection on either the positive or negative, (ground) of the RCA jack inside the TAD-150. Now that connection is off that contact completely. Should be an easy fix, if you know how to solder. Also, you should first try a different interconnect, (or swap the left and right one) just to be sure that the cable doesn't have the short in it.
tad-150 phono input problem
having a weird problem with the phono input on my tad150. the right speaker is no longer out putting any sound, or a very faint one, if anything. as a stop gap, i could wiggle the RCA cables coming into the back of the preamp, but this is no longer fixing the issue. all other inputs are fine. any thoughts?