Page 16
BlockHead™ User Manual Rev. B
(c) 2014 Blizzard Lighting, LLC
5. APPENDIX
A Quick Lesson On DMX
DMX covers (and is an abbreviation for) Digital MultipleXed signals. It is the most common
communications standard used by lighting and related stage equipment.
DMX provides up to 512 control “channels” per data link. Each of these channels was
originally intended to control lamp dimmer levels. You can think of it as 512 faders on a
lighting console, connected to 512 light bulbs. Each slider’s position is sent over the data
link as an 8-bit number having a value between 0 and 255. The value 0 corresponds to the
light bulb being completely off while 255 corresponds to the light bulb being fully on.
DMX data is transmitted at 250,000 bits per second using the RS-485 transmission
standard over two wires. As with microphone cables, a grounded cable shield is used to
prevent interference with other signals.
There are fi ve pins on a DMX connector: a wire for ground (cable shield), two wires for
“Primary” communication which goes from a DMX source to a DMX receiver, and two
wires for a “Secondary” communication which goes from a DMX receiver back to a DMX
source. Generally, the “Secondary” channel is not used so data fl ows only from sources
to receivers. Hence, most of us are most familiar with DMX-512 as being employer over
typical 3-pin “mic cables,” although this does not conform to the defi ned standard.
DMX is connected using a daisy-chain confi guration where the source connects to the input
of the fi rst device, the output of the fi rst device connects to the input of the next device,
and so on. The standard allows for up to 32 devices on a single DMX link.
Each receiving device typically has a means for setting the “starting channel number” that
it will respond to. For example, if two 6-channel fi xtures are used, the fi rst fi xture might
be set to start at channel 1 so it would respond to DMX channels 1 through 6, and the next
fi xture would be set to start at channel 7 so it would respond to channels 7 through 12.
Troubleshooting
Symptom
Solution
Fixture Auto-
Shut Off
Check the fan in the fi xture. If it is stopped or moving slower than
normal, the unit may have shut itself off due to high heat. This is to
protect the fi xture from overheating. Clear the fan of obstructions,
or return the unit for service.
Beam is Dim
Check optical system and clean excess dust/grime. Also ensure that
the 220V/110V switch is in the correct position, if applicable.
No Light Output
Check to ensure fi xture is operating under correct mode, IE sound
active/auto/DMX/Etc., if applicable. Contact service for more infor-
mation.
Chase Speed Too
Fast/Slow
Check to ensure proper setup of speed adjustment.
No Power
Check fuse, AC cord and circuit for malfunction.
No Response to
Audio
Verify that the fi xture is in “Sound Active” mode.
Adjust Audio Sensitivity, If Applicable.
Fixture Not
Responding /
Responding Er-
ratically
Make sure all connectors are seated properly and securely.
Use Only DMX Cables.
Install a Terminator.
Check all cables for defects.
Reset fi xture(s).
