AVR Freaks

... you are associated with a stage production of swingers? (it is Friday)

Nope.  Gershwin's Of Thee I Sing.  Openned tonight.  Dunno how it went, I was called in just to look at the revolve controller this afternoon.  Long story.

Have you checked the ususal suspects?

loose wiring, broken or worn potentometer, etc.

Yup.  Not any of those.

The whole unit (which contains the VFD) is itself part of a somewhat sketchy rental package.  The theatre came into possession of this >>enormous<< stage revolve (which half-fills a 53' truck) some years ago, but it didn't come with the motor unit.  For several years the revolve was turned by hand by stage crew.  I was one of them.  Then they started using a rental unit which was custom made, commissioned by another outfit to keep in their rental inventory, they had a lot of entertainment clients which used these kinds of things.  Then they were bought by a metal supply shop, who have kept the kit mostly for in-house use (it occasionally runs their bender, or something).  That shop is still happy to rent it out to the theatre occasionally, but they have no idea, and couldn't care less.

It has worked just fine for many years, many shows, many rentals.  Started acting up this week.

My best guess is that either the drive is in fact failing, but I think more likely is that the 'custom' controller assembly was poorly designed.  The VFD is of course just a small brick about 8"x6"x4", but it is mounted in a 19"x19"x12" electrical box along with a number of relays, disconnects, contactors, switches and other controls to select speed, direction, and control locale (panel or remote), provide safety interlocks, etc.  The cable routing internally seems reasonable enough, but the feed cable, motor cable, and foot pedal cable (that's the pot) don't appear to be shielded.  The manual is quite clear (and it's obvious anyway) that the control wiring must be run in separate conduits from either the mains input or the motor output wiring conduits to avoid the disruptive influence of noise on those cables.  No conduits, as this is a portable unit, and as I say apparently unshielded cables.  When I arrived at the theatre, the operator's station was a bit of a mess cable wise, with the motor output wiring snaking in and around a lot of other wiring (camera, monitor, clearcomm, other LX, etc), including the foot pedal cable.

I was able to get the 'UF' fault code to appear about a half dozen times over the course of my visit, but after I relaid all of the cabling in a tidy fashion (keeping each of the three motor unit cables clear of each other, and of all the other cabling present), I was unable to force a fault.  That is by no means definitive.  A sneaky, faulty connection somewhere, which I may have missed, and which might have been massaged in just the right way by relaying cables, could easily explain the disappearance of the symptoms.  Either way I'm hoping they make it through the week's run.  Only 4 performances.  It's an opera at the school of music.

For some years now the TD has been on the lookout for a complete system they could purchase, rather than be at the mercy of a rental unit which might vanish in the future, and which today has zero support.  While the VFD itself is not terribly expensive, the motor and the greater control system of which the VFD would be a part is quite prohibitively expensive.  The companies which manufacture entertainment equipment of this type don't really care about a relative small fry like this theatre.  He's looking at $20K or more, and that's when they can even get a sales rep to bother to return a phone call.