Just so others know, there are two small "
dimmer chips" (as called by the tech support guy) that can be switched (probably the same PSBs you referred to)-- since I was only using the
DMX OUT from the board, I was able to swap the two chips (the other for
DMX In) and signal flowed freely.
They are just RS485 transceiver IC's. Any company who makes
DMX capable equipment should always provide these IC's in their products as socketted dual in
line packages (the IC's with the metal legs that
point down and can be removed with a
flat blade screwdriver if you do not have a chip puller) IMHO. Quick fixes to be sure. For touring customers sometimes we would glue another chip upsidedown to the one actually being used. So if it blew, a tech could just pry the chip off and flip it over and away you go.
These transceiver IC's often blow because of
ground loops. If your
console is on one
power source and your dimmers are on another, the different sources of
power can have
ground at different potentials (ask anyone in audio about the fun with
ground loops). On stages or shoots we see this when some stuff is on
house power and some on generator.
Opto isolators are your friends in these cases.
Example: a few years ago I has a
Strand GSX
console and a
Strand CD80 dimemr pack blow. the transceiver chip in the pack controller blew (easy fix), the transceiver chip in the GSX
console also blew but a hole was burnt completely through the
circuit board because the earth potential on the
dimmer ground found a path to the booth's
ground because DC common was connected to the chassis via a 100ohm
resistor. Shouldn't cause a problem because the GSX has a
power brick and as such has no earth
ground. So what happened? When the
VGA monitor is connected, the GSX chassis is grounded via the shell and the
ground pin in the
VGA HD-DB15
connector. Oops. Booth
ground was not the same as
ground in the electrical closet back
stage. Double oops.
REad the number off the IC and oder one or two from a vendor and place them inside the chassis (secured of course) of your
console or
dimmer pack,
etc. for future emergencies - not that I like making easy money on easy repairs, but I hate to see cash strapped churches, schools, and small theaters spend money when they are ill equipped to do so.
Maurice Garcia
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