Picked up a Dentron Super Tuner for 100 on Craigslist. A little high for the unit but I have seen great reports on this manual, no frills tuner so I got it.
My first cursory visual inspection did not reveal any issues. Once I hooked it up I found intermittent issues and some wild results.
I opened up the unit to give a closer inspection. I found that the Acrylic stand-offs that the air inductors rest on were both cracked. This permitted movement of the caps and upon further inspection noted that one of the caps was not screwed on in the portion that is grounded. So....
I acquired two 1/2" square Acrylic rods from eStreet Plastics. Being a big fan of The Boss, I went with them as the supplier.
I acquired a brad bit to drill the holes for the mounting screws and the screws used to keep the caps in place. once drilled and mounted I had grounding issues as I screwed the caps through to where they were grounded to the chassis. After mounting the caps correctly, the tuner worked like a charm. It has been doing great.
So if you get one, the most common problems I have read about are that the Acrylic stand-offs are broken and that the inductor switch is not working. If you are finding that it won't tune at all it may be a grounding issue where the caps are grounded to the chassis by mistake or broken stand-off.