Model # TP1015, Ser.
Ok, this can indeed happen, in this model set, the tuner has Three, differing sections, what has happened is most likely the Tuning Voltage is faulty, as this is what causes this to happen.
This used to be a common fault, a few, many, years back, but as these older sets age and go faulty, they usually aren't repaired.
The Tuner is controlled by a Voltage Ramp, and Level. What happens is the Voltage that's being supplied has become faulty, and needs to be repaired.
When this happens it really is, the thin end of the wedge so to speak, and usually heralds a continuation of parts going faulty, as they all reach their end of life time. 10 - 15 years is a usual component's life, your set is over 17 years old. so i would tend to expect many more failures from now on,and indeed would question as to the practicality of repair. I would think, that any monies that would have been spent on repair would be put to better use being put towards a purchase of a new(er) unit.