N_Cook wrote:

As though the red of the colour wheel has gone dark with age. Instead of
vibrant red it is dull red/brown. Improved a bit with up to the limits
changes to the colour matrix, now dull red rather than dark brown for a
saturated red input . Not a leads problem , computer in and then computer
out to a monitor is fine. Video source is similarly affected. No loose leads
inside. "Service" manual has no schematic of course.
Is there a generic cause to this as it seems quite common across different
makes and models?

Is there any easy way to look at the colour wheel and see if the filter
really is the problem.

Could it be the lamp failing in some strange way? You can get a rough
idea of the spectrum if there is some light spillage which has not come
through the colour wheel (reflections coming out of ventilation slots in
the projector, for instance). Take one of the clear CDs that is used to
protect the bottom of a pack and, taking care not to get any
fingerprints on the disc, hold it so that the tip of your nose is poking
through the centre hole. Close one eye and move your head so that the
light from the lamp appears above the top edge of the disc.

If the light source appears sufficiently small, you should see a clear
spectrum with a good quantity of each colour.

--
~ Adrian Tuddenham ~
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www.poppyrecords.co.uk