Ok let me try this and see if any of you can help.
Sony G 70 projector.All was working fine. I replaced the green tube, with a
new Sony green tube.
All was ok for about 1 hour. Then the projector shut down with error 21,
115v HT supply fault.
It took some time but I found an other working PA board.
Replaced the PA board but still the same error 21.
Put the replacement PA board in a friends G 70 and all is ok.
Put the new Sony tube in my friends G 70 and it ran for 4 hours all was ok.
Put old PA and old tube back in my G 70 still error 21.
What should I look for now.

Graham

A swap with your friend involving the new sony green CRT and
replacement PA board?

Graham wrote:
....
Put the replacement PA board in a friends G 70 and all is ok.
Put the new Sony tube in my friends G 70 and it ran for 4 hours all was ok.
Put old PA and old tube back in my G 70 still error 21.
What should I look for now.