Two parts, one question, and the odds favor the driver
Drivers do the hot, stressful work — converting mains to a regulated current inside a sealed box that lives in the fixture's warmest corner — and their electrolytic capacitors age accordingly. Boards, by contrast, are passive rows of diodes on aluminum, and they mostly fail locally: one string dark, one scorched bead, dimming from cumulative wear. The base rates matter: a suddenly stone-dead panel is a driver until proven otherwise; a panel with a dark stripe is a board by geometry alone.
Behavior at switch-on refines the split. Dead-with-no-flash points at the driver's front end; a flash-then-off loop is the driver's protection tripping — sometimes against its own fault, sometimes against a shorted board; visible strobing or shimmer is the driver's regulation failing (or a dimmer feud, covered in the flicker branch below); and half-brightness with a clean geometric edge is a dead string on the board with the driver innocent.
Prepare before testing
- Screwdrivers for the fixture's service cover — access to the driver bay — with the circuit off at the breaker
- Phone camera — the driver's nameplate (output voltage range, current, wattage) is the shopping list
- A matched replacement driver — same constant-current rating and compatible voltage window — the definitive test and usually the fix
- Magnifier — scorched beads and cracked solder on the board are small but unmistakable
Kill the circuit at the breaker, not just the wall switch, before opening any ceiling fixture. Drivers store charge after power-off — handle by the case, never probe a sealed driver's internals, and leave mains-side wiring to an electrician if anything upstream needs work.
Check these areas first
- Driver capacitor aging. years of heat dry the electrolytics; output collapses or turns unstable — the leading killer
- Driver protection looping. flash-then-off cycling as the driver trips on its own fault or a downstream short
- One LED string open. a single dead diode or cracked joint darkens its whole series string — the geometric stripe
- Connector fatigue. the small driver-to-board plug loosens with thermal cycling and mimics either failure
- Dimmer incompatibility. TRIAC dimmers feeding non-dimmable drivers produce shimmer that looks like driver death
Diagnostic procedure
Observe the failure's shape, check the cheap mechanical suspects, read the driver's nameplate, then let one matched substitution divide the fixture into innocent and guilty halves.
Read the failure's shape at switch-on
Before opening anything, power the fixture and watch closely: totally dead with no flash, a brief flash then darkness (repeating or once), shimmer/strobe, or partial darkness with a clean edge. Note any recent history — a new wall dimmer, a lightning storm, gradual dimming over months. This observation alone assigns provisional guilt correctly most of the time.
Check the switch and circuit before the fixture
Confirm the wall switch and circuit with a simple test — another fixture or a plug-in lamp on the same circuit where practical, or a switch swap check by an electrician on suspicion. A dead switch or tripped breaker imitates a dead panel perfectly, and this two-minute check is free before any ceiling work.
Open up and reseat the driver-to-board link
With the breaker off: open the service cover, photograph everything, and reseat the small connector between driver and board — looking for browned plastic, loose crimps, or pins that back out. Thermal cycling loosens this joint over years, and a firm reseat resurrects a meaningful share of 'dead' panels on the spot.
Record the driver's nameplate
Photograph the driver's label: output current (constant-current rating in mA), output voltage window, wattage, and dimming type if any. This is the matching specification for a replacement — panels care about the current rating above all, and a 'similar' driver with the wrong current quietly cooks or starves the board.
Substitute a matched driver
Connect the matched replacement driver to the board (temporarily wired is fine for the test, with the breaker discipline maintained). Board lights fully and steadily: the old driver is condemned, and the repair is finishing the installation. Board still dark or still striped: the driver was innocent — the fault is on the board, and the bead-replacement guide takes over.
Inspect the board when the board is guilty
Under magnification, walk the strings: scorched or discolored beads, cracked solder at bead ends, browned board sections. A single bad bead in a string explains a whole dark row and is repairable with equipment and patience; widespread discoloration or many casualties across strings reads as end-of-life, and a replacement board (or fixture) beats bead-by-bead archaeology.
The panel that strobes instead of dying
Panel flicker sorts into three signatures. Shimmer that tracks a wall dimmer's position — worst at low settings — is a compatibility feud, not a death: a non-dimmable driver on a phase-cut dimmer, cured by a dimmable driver matched to the dimmer's edge type, or by retiring the dimmer to plain switching. Strobing that developed on an undimmed circuit is the driver's regulation failing as capacitors age — the same substitution test above convicts it, and the same matched replacement cures it. Rhythmic blinking every second or two is protection looping: occasionally the driver's own fault, but worth one board inspection first, since a shorted string can innocently trip a healthy driver. In all three, the board is rarely the flickering party — boards fail dark, drivers fail noisy.
Reading a driver label like the board depends on it
Constant-current drivers are specified by output current first: a board built for 300 mA driven at 450 mA runs bright, hot and brief; driven at 150 mA it sulks at half light. Match the mA exactly, then confirm the board's operating voltage falls inside the new driver's window, then match wattage with headroom. Dimming class matters too — a TRIAC-dimmable driver behind a plain switch is fine, but a non-dimmable driver behind any dimmer re-creates the flicker branch above. The original label photographed in step four answers every one of these; when the label is cooked beyond reading, the fixture maker's part list — searched by fixture model — is the honest second source.