"Ancient_Hacker" wrote in
ups.com:


Sam Goldwasser wrote:
So my trusty scope is acting up.

At normal and low intensity, there is a chopped appearance to
the trace at a few hundred Hz. It's variable and at times,
increasing intensity also causes change in focus, and/or the
intensity doesn't go as high as it should.

I assume a problem in the HV.

Thanks for any info.


Maybe check the LV first.

I agree;first,assume low voltage power supply problems.
EVERYTHING works off them.

(Sam,you oughta know this!)


The bridges on this scope tend to go
half-bad, turning the bridges into half-wave rectifiers. Also the
filter caps can lose capacitance. Put the scope on a variac, turn the
variac down to 100 volts and put a scope on the PS test points. If you
see 60 Hz ripple, then it's the diodes, if it's 120Hz ripple, its the
capacitors.

The HV power supply has like a voltage quadrupler. Maybe a diode or
two has shorted there?

Not likely,as reduced anode HV would result in a much dimmer and enlarged
displayed signal(in both dimensions),and the cal would be greatly affected.
Also,I don't think the HV would continue running with a shorted diode in
the multiplier. I believe the HV fuse would blow first.

BTW,at some point,increasing intensity will definitely affect focus.
The CRT cathode emits from a larger area,and gets worse as the CRT ages.

--
Jim Yanik
jyanik
at
kua.net