Power steering locks up

[JMBT]

I had the same thing on my Volvo a few years back. I went through everything. pS fluid, pump, filter, steering box, even king pins, at my wits end I replaced the entire steering shaft from the box to the wheel. Volvo has an articulating steering wheel that puts the upper U joints, (the ones inside the cab) in a bind in certain wheel positions. The shaft ended up fixing the issue. Just wish I had tried it first. I was reluctant because there was no play in any of the U joints, but it fixed the issue!