Richards,
OK, 850 kHz is a more expected harmonic of a switcher.
Since it is two years old, I am thinking maybe you have a previously
good filtering capacitor starting to change value or go open circuit,
increasing the inherent harmonics of the switcher.
You may need a scope to look across each capacitor. You would need an
isolated (for AC) high voltage probe in the oscillator section, but that
might also load the circuit and stop or change the oscillation
frequency. Likely the main suspect capacitors will be electrolytics in
the section after the bridge rectifier, ie the DC section.
You can look at those with a regular 10:1 scope probe, since one side of
the filters will likely be the negative DC terminal.
Look for discoloration or signs of leaking of any capacitor in the
supply. Look for any bad solder joints or loose connections leading to
loss of filtering.
You might consider sending the supply in for repair with a good complete
description of your observations, but call them first to discuss the
apparent problems. Switchers are the hardest supply to troubleshoot and
repair, if you are not familiar with their circuits and operations.
There is also a slight chance you have a bad diode in a bridge
rectifier. One diode open might upset the apple cart.
Also, have you changed the DC power lead length or size of conductors
just before the problem was noticed? Sometimes rearranging a shack
brings undesired problems to notice.
Other things in this category are rearranging and thus getting the rig
too close to a switcher supply, thus enhancing magnetic coupling.
Once you have a Good 963, (can you borrow another in your area?) you can
do side by side comparisons with a scope and speed your conclusion of
what is right or not.
Good Luck!
73,
Stuart Rohre
K5KVH
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