Troubleshooting & maintenance

No output: diagnose in five steps

Five stages from mains to load, each with a measured pass criterion: 198 to 242 V AC, CV reads nameplate open circuit, CC at its window ceiling is normal, a 5 m 24 V strip reads about 8 ohms.

Last updated：2026-11-02

"Light is out, swap the driver" is the most common action on site and the one most often done wrong. In a no-output call the driver itself is far from the only cause - upstream supply, terminal crimps, a shorted load or an open strip all present identically. The point of the ladder is not to look professional; it is to narrow the fault to one stage with a single multimeter so the replacement is right the first time.

The one-sentence rule: bisect from upstream down, one number per stage

The five-step decision flow

Step 3 is where most misdiagnoses happen: constant current open-circuit voltage

This single point causes more unnecessary swaps than anything else. Disconnect the load on a constant-current driver and the output rises to the window ceiling - that is how the topology works: the current setpoint is fixed, and with no load the only thing it can do is push voltage up.

• A constant-current unit with a 12-48 V window reading 46-48 V open circuit is normal, not "overvoltage damage"
• Constant voltage is the opposite: open circuit must equal nameplate, so a 24 V unit should read 22.8-25.2 V (plus or minus 5 percent); zero is the anomaly
• Judge on voltage only - never by whether it sparks

Step 5: clear the load question with the resistance range

Normal strip resistance is computable, so any deviation is a finding:

R = U x U / P

24 V, 5 m, 14.4 W/m - P = 72 W - R = 576 / 72 = 8 ohms
12 V, 5 m, 14.4 W/m - P = 72 W - R = 144 / 72 = 2 ohms

Measure two commonly missed points while you are there:

• Terminal contact resistance: the drop from the driver output terminal to the strip start; under load anything above 0.5 V means re-crimp (the full method is in the voltage drop and cable size table)
• 0-10 V signal pair: short the two signal wires at the driver and the light should go to minimum; left floating, most units return to full. If floating still gives nothing, the fault is in the driver or upstream, not the dimmer

Three things that look like a dead driver but are not

1. Triac dimmer stuck at minimum: at very low output the driver never starts. Turn it to maximum; if still dark, bypass the dimmer and run mains straight in as a check.
2. Thermal protection not yet reset: re-energising immediately after a trip does nothing. Wait 30 s to 2 min; if it lights normally afterwards, nothing is broken.
3. Several units dark at once means look upstream: multiple drivers failing simultaneously is close to impossible. Check the breaker and the group switch first - the same fault domain as inrush current and breaker sizing.

Evidence to record before you swap (copy this list)

1. Nameplate photo of the driver (model, input and output ratings, certification marks legible)
2. Four readings: input voltage, open-circuit voltage, loaded voltage, load resistance
3. Installation photo: sealed cavity or not, metal surface for heatsinking, how many units packed together
4. Symptom wording: dark / flashes then dies / runs a few seconds then dies / dies only at low dimming
5. Which of the five steps you have already run (tick them off)

Constant-voltage units K01, S01 and H01 and constant-current units R01 and X01 all go through these five steps; only step 3 differs (CV reads nameplate, CC reads the window ceiling). Power and cable sizing is done in the LED driver sizing calculator; a light that comes on but flickers is covered in the flicker troubleshooting manual; how far a 0-10 V pair can run is in 0-10 V signal cable maximum length.

© 2026 YFX. Figures are for selection purposes. Always follow the datasheet and local wiring regulations for final installation.