Okay, I am about ready to pull my hair out on this one.

Equipment is as follows:

2 Technics SL-1200 MK2
Rane Sixty-One Mixer
Macbook Pro (OS X 10.8, Serato 2.4.4)
Shure Whitelabel Carts
Serato Performance Series Vinyl

Little bit of history with this issue:

2 weeks ago I show up to a gig and had been informed that the club had their own Technics so I didn't need to bring mine. Get there and setup, I brought everything but the tables themselves. I have an issue with the left deck, the scope on the Serato setup screen shows a vertical line. I know that means that the left channel on my mixer is not receiving input. I tried multiple things to troubleshoot.

First I switched needles to see if the problem switched decks, nope it stayed the same. I then tried a different set of needles that I know are good and I carry around as spares, nothing changes. Next I flip the timecode over to the 10 minute side (which had never been used) and that doesn't change anything, then I grabbed the timecode from the other (working) deck, still have a vertical line.

Okay, so now I think I've eliminated any of my equipment as far as the turntable and it must be an issue with the wiring either inside the tonearm or it's a short in the RCA cables. Just for good measure I go ahead and swap input channels on the mixer, this time the issue does change sides on the Serato scope and now I'm seeing it on the right side. So that seems to also confirm that it was an issue with the club's turntable. Went on to spin on one deck and internal and everything was fine except for the obvious annoyance of using a single deck.

I talk to my buddy who had booked me and spins on Thursday nights there and he says he never has any issues with these tables, also the following Thursday confirms that they are working fine for him. That was where I first starting saying WTF?

Anyway, fast-forward to the next Saturday, I'm booked in the same spot, except this time I bring both of my own turntables to the gig. I hadn't been experiencing any issues with them so I figured this would be the best course of action.

I arrive and figure I might as well give the house equipment a shot again, same issue arises and I don't go too indepth with my troubleshooting of their equipment because I have brought my own. Hook up my tables, and..... I am now having the same issue with my own equipment. How could this be? Well at that point I go through all the same troubleshooting steps as above and am not able to find a solution. I spend another night spinning minus one deck.

Get home after the gig (this past week) and hook up the tables and they work fine. Okay, that makes sense to me because they had always worked in the past whether I was home or on a gig. Last night I spend a couple hours practicing on them and they are working fine.

So, today, I received replacement tonarm assemblies from DJ Henray Customs. These are complete assemblies from the tonearm all the way to the RCA's and they are refurbished not brand new. This was something I had planned on doing for a while, it wasn't because of this issue that I replaced the assemblies, but rather because I had experienced control tone issue (intermittent) where the signal would drop in and out. They had poor soldering done on them, mismatched cheap RCA's and I just wanted something that would work.

I dropped the tonearm assemblies in put back together the tables, and go to test them, and I am confronted with the missing left channel issue again on one deck!!

So I of course went through and did all the same troubleshooting steps as above again, but since I was at home I took it even a step further.

I tried the good deck in all four channels of the Sixty One and confirmed that they all were working and that I had a proper scope readout on the Serato software. Next up I decided to see if the issue was still there without the software in the equation. I hooked up the faulty deck and allowed the control tone signal to passthrough directly so that I could hear the tone through my speakers. When I adjusted the "Pan" knob to the left I heard nothing, back to center and right and I hear the control tone. I also grabbed my old Allen and Heath mixer off the shelf and plugged it in and found the same thing, missing left channel.

So now I'm back to thinking it has to be the tonearm assembly, that even makes sense because I had swapped it out earlier, right? In order to test that theory out I used my multimeter to do a simple continuity test, inside the end of the tonearm are four gold contacts that correspond to Right channel +/- and Left Channel +/-. I tested each of these contacts with one probe while holding the other probe on the contact surfaces for the left and right RCA's and measured a small amount of resistance on each (avg 0.9 ohms) which is what I expected and confirmed that there was continuity. Nothing wrong with the tonearms that I got from Henray (they were in great condition cosmetically too).

So that is where I'm at now, and to me it seems like I've hit the end of my troubleshooting rope, anybody else have any suggestions? I'm stumped.