Sliders don't work

[bluesmangc]

I was recently given a Tascam 788 under the assumption that it was working. As I was learning it's operation, I discovered the sliders don't work. I have tried the fader matching and it is set to real. The levels do show some change on the screen but very slowly and only a small portion of the scale. I can get one of these recorders on ebay for about $100.00 so I don't want to put much into it. Is it worth pursuing?