Basics 12. Troubleshooting and a glossary of terms
The final lesson of the course, and the most practical one. The light has not come up, half an hour to doors, palms sweating. At that moment the main thing is to work through the whole system calmly and in order. Let’s gather everything we have covered across eleven lessons into a single fault-finding routine. And at the end — a cheat sheet with every term in the course.
The main principle: change one thing at a time
Three rules that turn panic into work:
- Change one thing at a time. Swapped a cable? Test. No luck — put it back and change the next thing. If you change three things at once, you will never learn which was to blame, and it will happen again at the next event.
- Halve the system. The chain «software → interface → cable → fixture» is checked from the start: first make sure data is leaving the computer or the physical desk at all, then that it reaches the first fixture, then the last.
- Start with the simple and free. Address, mode, shutter, cable — before you conclude that «the fixture has burnt out».
Five questions in thirty seconds
Before taking anything apart, answer five questions. They cover half of all cases.
- Are the fixtures actually plugged in and are their indicators lit?
- Is the interface connected and does the software see it?
- Is blackout engaged, or the grand master pulled down?
- Do the addresses match in the software and on the fixture?
- Does the channel mode match (6CH/9CH/14CH) the selected profile?
Points 3–5 are the three most common causes of all.
Fault-finding by symptom
Nothing works at all
Not a single fixture responds.
- Check whether the software sees the interface. If not — plug it into a different USB port and check the driver.
- Check blackout and the grand master in the software.
- Push any channel directly in the raw channel mode (lesson 2) — that rules out mistakes in scenes and profiles.
- Check the cable from the interface to the first fixture — replace it with one you know is good.
- Connect one fixture straight to the interface with a short cable. If it works, the problem is in the line, not the fixture.
The wrong fixture or the wrong parameter responds
- The wrong fixture — nearly always mixed-up addresses. Compare your address map with what is set on the fixtures.
- The right fixture but the wrong parameter («I move colour and the strobe changes») — the channel mode does not match (lesson 3) or the wrong profile is selected.
- Two fixtures behave as one — they share the same address.
- Fixtures affect each other — the addresses overlap and the channel blocks collide.
One fixture is silent while its neighbours work
- Check the shutter and master intensity on that fixture (lesson 4).
- Check that the fixture is in DMX mode, not auto/sound (lesson 3).
- Replace the cable going to it, and the cable coming from the previous fixture.
- Swap it with a neighbouring fixture in the chain: if the problem travels with the fixture, it is the fixture; if it stays in place, it is the cable or the connector.
Everything flickers, twitches, lives its own life
Classic line problems (lesson 8):
- Fit a terminator into the OUT of the last fixture.
- Make sure the cables are DMX, not microphone cable.
- Check that there is no star connection and that 32 fixtures / 300 metres are not exceeded.
- Separate DMX cables from power cables.
- Try a different DMX controller: cheap models on a loaded computer sometimes produce a ragged stream.
Part of the chain is dead
The first fixtures work, the distant ones do not. Look for the break: replace the cable at the «works / does not work» boundary, check that the intermediate fixture is powered (on many models the signal only passes through OUT when the fixture is on), check the connectors.
A fixture flashes on its own, ignoring the desk
It is in standalone mode. Check the fixture’s menu (Auto, Sound, Slave), the tenth DIP switch and the Auto/Program channel in the profile.
Nothing comes out over the network
If you are using Art-Net or sACN (lesson 9):
- Computer and node are on the same subnet.
- The Windows firewall is not blocking the software.
- The universe numbers match (the classic mistake is being off by one).
- The connection is wired and unused network adapters are disabled.
Symptom-to-cause table
| Symptom | First thing to check |
|---|---|
| The software does not see the interface | Driver, another USB port, cable |
| Nothing lights at all | Blackout, grand master, shutter, power to the fixtures |
| The wrong fixture lights | Addresses |
| The wrong parameter changes | Channel mode, profile |
| Fixtures «duplicate» each other | The same address |
| Flicker, twitching | Terminator, cable type, star wiring, line length |
| Distant fixtures are silent | A break, a connector, power to the intermediate fixture |
| One fixture dances by itself | Standalone mode (Auto/Sound/Slave) |
| A head went the wrong way | Reset the fixture; inversion when rigged |
| Movement is stepped | No 16-bit mode / a profile without fine channels |
| Nothing goes out over the network | Subnet, firewall, universe number |
The emergency kit
All of this is inexpensive and fits into a small bag — and it saves events:
- two spare DMX cables (one short, one long);
- two terminators;
- XLR 3↔5 adapters;
- a spare USB interface and a USB extension lead;
- a mains extension lead, cable ties, insulating tape, masking tape;
- a torch and a multitool;
- a printed address map.
Checklist before the event
- Fixtures are rigged and secured with safety cables, cables are not taut.
- Power is spread across circuits, the fog machine is on its own line.
- The DMX line is wired as a chain, with a terminator at the end.
- The interface is connected and the software sees it.
- Every fixture responds — tested one by one through direct channel access.
- Heads have run a Reset and been driven through their extreme positions.
- Scenes and chases have been played through from start to finish.
- Checked from the audience’s position: nothing shines into eyes, faces are lit.
Glossary of the course
| Term | Meaning |
|---|---|
| Address | The number of a fixture’s first channel in the line |
| Art-Net | A protocol for carrying DMX over a local network |
| Beam | A head with a very narrow, dense beam |
| Blackout | Instantly killing all the light |
| Blind | A mode for preparing a scene without showing it in the room |
| Blinder | A fixture for dazzling flashes into the audience |
| BPM | Tempo in beats per minute; chases step to it |
| Chase | A sequence of steps at a set tempo |
| Channel | Control of one parameter; value 0–255 |
| Channel mode | How many channels a fixture takes (6CH, 14CH…) |
| CMY | Smooth colour mixing with cyan/magenta/yellow filters |
| Colour wheel | A mechanical set of colour filters |
| Crossfade | A gradual transition between two states |
| CTO / CTB | Filters that make white warmer or cooler |
| Dimmer | The master intensity channel; also a pack for controlling incandescent lamps |
| DIP switches | Switches on a fixture that set the address as a sum of weights |
| DMX512 | The lighting control standard: 512 channels per line |
| Fade | The transition time between states |
| Fine (16 bit) | The second, «fine» channel of a parameter; with the first it gives 65,536 steps |
| Freeze | Freezing the current picture |
| Frost | A filter that softens the beam’s edges |
| Gobo | A stencil that draws a pattern in the beam |
| Hazer | A machine producing even haze so beams are visible |
| HTP | The merge rule «the highest value wins» (intensity) |
| Interface | The translator from USB or network into DMX; a «dongle» |
| LTP | The merge rule «the latest value wins» (colour, position) |
| Patch | The table of fixtures with addresses and modes |
| Pixel fixture | A fixture where every segment is controlled separately |
| Playlist (cue list) | The show’s running order |
| Preset | A stored value for one property: position, colour, gobo |
| Prism | An attachment that multiplies the beam |
| Profile | A description of the channels of a specific fixture model |
| RDM | A two-way layer over DMX: interrogating fixtures and remote addressing |
| RGBW and beyond | LED sets: +white, +amber, +ultraviolet |
| sACN (E1.31) | The second standard for carrying DMX over a network |
| Scanner | A fixture that deflects its beam with a mirror |
| Scene | A saved state of the light |
| Shutter | The «closed / open / strobe» channel |
| Splitter | A DMX line splitter/booster |
| Spot | A head with a sharp beam and gobos |
| Submaster | An intensity fader for a group or a scene |
| Terminator | The 120 Ω plug at the end of the line |
| Universe | One complete DMX line: 512 channels |
| Wash | A fixture or head with wide, soft light |
| XLR | The DMX connector; 3 or 5 pins |
The course is over — what next
You now know the essential minimum about DMX before you start work: how the protocol is built, what channels, addresses and profiles are, what kinds of fixture exist, how they make colour and movement, how a line is assembled, what to drive it with from a computer, what words lighting desks speak, and how to plan the light in a room.
Next comes practice. SvetoMaster has a separate series of lessons about the software itself: from a first mini-show to running a concert live, playlists and the AI assistant. They will read easily now — every term in them is already familiar to you.
- All lessons about the software — step by step, from first launch.
- User manual — a reference for every feature.
Not installed the program yet? Download SvetoMaster — you can start building a show right now, without a single fixture: everything is visible in the 3D visualiser, and the hardware connects later.