Many things can cause banding including faulty mirror galvos and
electrical interference, but in our experience the commonest is (as
several others have said) a laser which is going off.  Gary Templeman
(our local BioRad engineer, who has been on a course at ILT) explained
that the cause is the feedback mechanism - it tries to get the power
up to the correct level but in so doing takes the voltage too high,
so it cuts out, resets, and so on .... Again, in our experience,
readjustment will help for a while - but it's definitely better when
Gary does the adjustment than when I do, so it's clear that proper
training helps here!
 
In the light of this explanation it seems clear that running the
laser on low with less ND is bound to help.
 
BioRad Australia have developed a mod which *should* greatly extend
the effective life of an Ar/K laser.  This links the laser power to
the laser shutter switch, so it only goes onto full power when you
are actually scanning your sample.  At all other times it is automatically
switched to low.  Since most people are only scanning for a small
proportion of the time the laser is on the potential saving in tube life
is large.  (Top marks to BioRad for this one!)  They are fitting this
free of charge to all customers in Australia as and when an engineer
calls at that site.  I've no idea what the policy is elsewhere but it
might be worth enquiring (it only involves a relay and some wiring).
 
                Guy Cox
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