Actually, I have no idea. The questions I would be asking are:
1. How much do you have invested in it?
2. Has it sewed for you at all, and if so, did you like the result?
3. How much are the parts (if you can get them)?
4. How confident are you that the tension is the only issue?
5. Is the machine for your use or do you plan to sell it?
6. If you plan to sell it, what do you think you can get for it?
7. If you plan to sell it, how much time are you willing to invest in it?
It's really a question of how much is reasonable to invest in it. Since it's electronic, how old is the machine and how long can you expect the machine to last?
I don't know the answer to those questions and have no experience with electronic sewing machines, so I can supply questions, but no answers.
bkay