Originally Posted by Professor Shadow
Don't forget that this is a two-pair system and it is polarity-sensitive. In addition, the second pair's polarity must be reversed, as in tip-yellow, ring-black.

Yeah, it's been a while. I do remember those Goldstar flat pack KSUs having some kind of issue with polarity reversal on the second pair. Maybe it knocked out the paired station if reversed? I can't say for sure.