The three places I'd check for issues first would be:
1.)
DMX run between the
console and the dimmers (this one is less likely, as issues with this cable tend to be intermittent [randomly flashing lights, etc], but it is also one of the more accessible things to check. Try running a different cable and see if the problem continues.
2.) Anything having to do with a
protocol converter (if one exists in your
system).
3.) The dimmers themselves. I'm thinking this is the most likely issue. Now, comes the fun of playing investigator and ruling things out.
Is there any particular
pattern to this problem? Are the dimmers showing any kind of overtemp event? Are they the same instruments acting up every time, or does the problem "move around"? Are they on the same pack or in adjacent channels within a pack or rack? What else do these fixtures have in common? I'm assuming that the
system has worked fine for quite some time -- has anything changed/moved around recently, other than the
console? Any
power surges reported in the building lately?
I doubt it's a problem with the 120v wiring leading from the dimmers to the fixtures (as this problem would also surface as intermittent flashing, tripped breakers,
etc).
There is also the slight possibility that somehow your
console's
dimmer curves have been changed for those channels (assuming that it is a predictable, repeatable problem).