52Z575 - How to resolve "pincushioning"?

[Ratman]

Have a buddy that just bought this set. Presently, the only issue I see is that there is slight pincushioning that's apparent when watching 4:3 material.

Has anyone found any info about how to adjust?
(I quickly read through the service manual, but nothing appeared obvious)

[lingen]

What is pincushioning?

[Ratman]

The sides of the picture (grey/black bars) look similar to this:

) (