Re: 7904 excessive shadow/flare

Chuck Harris
 

That's wonderful, but the flare exists when there is only the single
spot on the screen. Why in your theory, does the center spot not
change?

This is a completely normal effect caused by the mesh lens, and the
high energy electron beam.

The high energy beam allows this diffraction to be high enough energy
to light up the phosphor. The slow speed allows the phosphor even
more time to bank up its electrons and make light.

This is normal for the 7904 CRT. It happens on my 7904's, and my
7854 to exactly the same degree.

If you don't like it, turn the intensity down to a more reasonable
value.

-Chuck Harris

Roger Evans via Groups.Io wrote:

To my eye each of the shadow peaks and troughs of the sine wave lies on a straight line joining the real peak/trough to the CRT centre, but farther out. This should be very obvious at say 100msec/div. I would guess the probable cause is the CRT cathode voltage dropping out of regulation due to a HV capacitor failure. If you don't have a HV probe you should be able to see the ripple on the feedback to the regulator.

Regards,

Roger



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