Tips on buying used MTV?

May need to get a used MTV-7000D to complement an old TV with analog tuner
Thinking of this model because
a. It has all necessary output ports (Component, S- and Composite video outs) (old TV concerned has Component input)
b. Standard size means easy stackability with other AV equipment

What should I watch out for when buying used MTV units?  What should I be checking, apart from the usual components (HDD, MB, chipset etc.)?

Feedback appreciated