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If the purple band does not appear in pictures when you download them on computer, then the problem is a faulty LCD screen or a bad ribbon cable.
If the purple band appears in pictures even when you watch them on a computer, then the problem is a faulty CCD sensor.
In both situations the repair requires complete disassembling and must be done by a technician.
If it is CCD , then Canon may cover the out of warranty repair, call them back and ask again stating that is CCD problem.
You can also get an independent quote on repair here:
Repair.
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