Channel Plus 3025 Modulator Issue

[shotgunmess@xxxxxxxxxxx]

I have been using one of these for about 3 years.  The first year and a
half it worked fine.  I was modulating A on Channel 80, and B on
Channel 82.  Suddenly 82 became unwatchable.  I assumed this was due to
a change in my cable stream.  I wound up buying another unit only to
experience the exact same results.  I returned it, and started
modulating on only channel 80 and adding a multi switch into the
equation, which allowed me to switch between multiple sources.

Yesterday I started playing around again.  It seemed that I could
modulate the B modulator to 80, but the A, no matter where I set it,
would show up in the channel lineup around 69.  I finally found that
putting it at 100 worked ok.  I suppose this is a solution to my
problem, and everything is ok for now.  But I'm curious as to what
caused this.  Any ideas?  Maybe a Channel Plus guru can shed some
light.