Turn Table Decision

I bought my first TT in 1979 while a freshman in high school -.a Dual CS508 ULM, and I still have it, currently with an inexpensive Audio Technica cartridge, I was using it until very recently, when I received in a trade a Marantz 6200 with a Shure v15 type IV cartridge. The problem is the Marantz has a hum. Both channels, volume-dependent. I reconnected the Dual and there is no hum, so I am pretty sure it is the Marantz. I played around with my multimeter, and I cannot find anything obvious. 

So my question is: Do I spend $100-$200 (guessing) to fix the Marantz, or do I just stick with the Dual (or do I suck it up and buy a better TT)?

The rest of the system, if it helps: Acoustic Research AR3a speakers; Audio Research M100 tube monoblocks; JENA Labs interconnects; conrad-johnson PV12 tube preamp with phono stage; and a McIntosh MR67 tube tuner.

Thanks.