Power supply issue?

New here....having channel/power supply issues with amp and/or graphic EQ. Hoping to gain some knowledge and suggestions to correct the issues. I regularly loose left channel....if I partially unplug the EQ (Pioneer SQ-550) to a half-way loose-ish insertion I can regain stereo. First guess is bad power cord, but I'm no expert. Looking for other thoughts, recommendations and/or actions to take to correct the issue.