Mein ny ek 2nd hand monitor purchase kia hy , bazahar woh sahi kaam ker raha hy magar off position per uski screen per colours aarahay hain (upper left and right corner & at mid also), what does it means.

1) kia yeh repaired set hay?
2) picture tube ka masla hay?
3) Mein is ko isitarah istamal kerta rahoon yah change karoon?
4) else?

While purchasing used monitor what are the things we must check??????


Help?