Linn LP12 I channel louder?

After swapping about between my Jolida JD9a phono amp and the MC part of my Yamaha as-100 have isolated the source of one channel weakness to my LP12.Its a 1980’s vintage with a 2/3 year old Dynavector DV-20X2L.My question is where do I start to track down the left channel bias? Its slight but a twiddle of balance control makes a huge difference.Its not amps or speakers as CD, Radio, PC all good and balanced.
Anti skate has no effect, still left bias. As I said its slight, so when adjusting skate I almost felt it fixed but two or three minutes in and its still there. Thanks for the idea.
Remove and replace turntable outputs  in reversed position ....left into right, right into left.  If the louder channel changes,the problem is probably  the turntable/cartridge,  if not, I would  move the furniture around to change the room acoustics
It the table absolutely level?
Swap the cartridge leads. If that changes it, then there’s an issue with alignment or the cartridge itself. Check azimuth. Sometimes, it just might just be the way it is with that specific cartridge and not much you can do about it...
Astonished how out of level it was when I put a spirit level on it. Noromance you were correct! Thank you and everyone else that made suggestions. Definitely better but still don't trust my ears yet, but lets call it done.
I had a 17D2 do that after using it for too long with the bias set incorrectly, I was trusting the bias scale on a Rega 300 arm. When I looked with a loup the cantilever was slightly twisted along its length and offset to one side a little, that was a lesson for me.
Off level would have a similar effect if not corrected soon enough. You might want to review how you set bias. Hint, start with a level table.
I guess the lesson to all is make absolutely sure your turntable is set up correctly. It only requires a few inexpensive tools, a test record and practice. Never trust a dealer or even manufacturer to get it right. 
For sure the lesson is check the simple things are right on your setup. I didn't question the setup before as it was completed by a professional in my home which I paid for.