Thanks David I will look at your hints tomorrow


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oups.com...
Have you swapped the blue and red convergence yokes to confirm it is
actually the circuitry to the blue. Until you KNOW it is not the
picture tube or yoke, it seems the divide and conquer troubleshooting
has not started.

Think about on the most basic level, what can shift the beam.
The last time I saw this odd problem that did not appear to be effected
by any spray cooling on any part of the convergence circuit it wound up
being in the picture tube/yoke assembly.

I have seen both the tube and the yoke cause this problem. In your
case I'm thinking it is the yoke since it is only one corner. I would
guess that there are some windings in the convergence yoke causing the
problem.

I have seen blue picture tubes cause convergence/geometry shift when
the internal tube structure gets warm, but only across a larger
quadrant as the internal metal would 'bend' as the gun assembly would
heat up. It never acted up on the green or red as the blue tube was
the one mounted 'upside down'.

I have also seen water contamination inside the crt coolant cause an
effect just like yours described. As the coolant and the face of the
tube would get hot enough, the water and air would cause the air bubble
to get larger, which obviously would shift the apparant beam landing on
the rptv screen. This is an easy one to rule out, look into the tube
with the lens off when it is acting up. If the area that is shifted
has the bubble, viola.