If you think the ST7 was heavy, you should have seen the ST-4! The ST 5,6,7,8 were flimsy by comparison.
IF the drive electronics and controls are functional, it is an OK turntable, but not worth putting much money in if the electronics are dead. If the electronics work it will probably need a new belt.
What cartridge is in it? IF you need a new cartridge, I would suggest a medium compliance cartridge as this has a good tonearm, not a great tonearm.
Another problem, if this is the model that used rubber rollers to keep the arm in alignment (ala the ST-4), if those have flat spots on them, the rumble could kill a woofer. I don't know if repairing the rollers by
www.terrysrubberrollers.comwould be affordable for this unit.
Ken