Fault Finding - NJD Electronics IQ-MX80 User Manual

User Guide
it can determine which data is addressed to it. It then uses this
data to move a motor or set a brightness level as required by the
controller.
As the DMX system can transmit as much information as
512 analogue control wires down a single cable, it has to
transmit very quickly, in fact, at a frequency 12 times higher than
the highest audio frequency. Anyone who has used long leads for
audio will realise that it is difficult to do without losing the higher
frequencies.
To make the DMX system work at such high frequencies, it
requires special circuitry and special cable. Cable can be designed
to pass high frequencies with no loss if it has the correct
resistance connected at each end, this resistance is called the
characteristic impedance of the cable. DMX cable has a
characteristic impedance of 120W.
All NJD DMX products with ¼" jacks are designed to ensure
that the resistors are connected automatically. Without them, the
signal reflects off the end of the cable and interferes with the new
data coming the other way. If the cable is not correct, the system
will not work. Products with XLRs require a DMX terminator to be
fitted to the DMXout connector of the last lantern in the chain -
refer to the lantern user guide.
Most good quality low-capacitance screened twisted pair
cables will work, but twin individually screened will not. Also, if the
cable is split or joined other than end-to end, the system will stop
working.
• Lanterns do not operate
Break in DMX cable between controller and first lantern.
DMX Cable shorted out*
DIL switch #128 turned on (should be off)
• Only certain lanterns operate
break in DMX cable*
DIL switch #128 turned on (should be off)
• Lanterns operate erratically
Unterminated cable in output socket of last lantern.
poor or intermittant DMX earth connection*
© N.J.D. Electronics 1997

Fault Finding

IQ-MX80
-Page 10-