Emergency light circuit boards (charger/driver/transfer) are the brain of a unit: they charge the battery on normal power, sense outages, switch to battery, and drive the LEDs for ≥ 90 minutes. Whether you’re looking at a standard emergency light board, a 6v emergency light circuit board in a compact unit, or a 12v emergency light circuit board feeding remote heads, the same core functions apply. This guide explains symptoms, quick diagnostics, and when to repair vs replace—so you pass inspections without guesswork. For the big-picture life-safety overview, see the Emergency Lighting Guide.
Overview: What the Emergency Light Circuit Board Does
The main emergency light board (sometimes split across two small PCBs) typically provides these functions:
- Charging: keeps the battery at the proper state of charge on normal AC power (120/277 V) using an onboard charger/driver circuit.
- Transfer: senses loss of AC and switches the unit to battery in < 1 second.
- LED drive: regulates lamp current so the unit meets the UL 924 runtime (≥ 90 minutes) whether it’s a 6 V or 12 V system.
- Status: provides indicator LEDs (and on self-test models, logs/diagnostics).
In other words, the LED emergency light circuit board is the control center for charging, transfer, and illumination. When these functions drift or fail, you’ll see dim/unstable lamps, blinking fault indicators, or batteries that never seem to charge—classic signs of an emergency light board problem, not just a bad lamp.
Common Symptoms & Likely Causes
- Unit doesn’t light on test: dead/loose battery, blown fuse, open LED head, failed transfer relay/board.
- LEDs flicker or dim on battery: weak battery, wrong lamp load, failing constant-current driver on the circuit board.
- “Charging” forever: battery end-of-life, bad charger circuit, miswired AC input (incorrect lead tap).
- Status LED shows fault: self-testing models flag battery/charger/transfer; decode with the unit’s legend.
- Will not pass 90-minute test: battery capacity too low, load too high, or the emergency light circuit board not regulating output correctly.
If batteries and heads test good but problems remain, treat the main PCB as the suspect—especially on older units where the original emergency light board has seen years of heat and cycling.
5-Minute Diagnostics (Safe & Simple)
Before opening the housing, de-energize the circuit and verify lockout/tagout as required. Then:
- Visual check: look for heat discoloration, swollen batteries, pinched wires, loose connectors, or obvious damage on the emergency light circuit board (burnt components, cracked traces).
- Verify AC input: confirm correct lead (120 vs 277 V) and tight neutral/ground. If a transfer device is used, verify its wiring.
- Battery test: measure open-circuit voltage; check age/date stamp. Swap in a known-good pack if available.
- Load sanity: sum the wattage of all lamp heads (on-board + remote). Compare to the unit’s 90-minute rating.
- Board connections: reseat low-voltage plugs; check fuses. Inspect for cracked solder joints near high-heat parts on the charger/driver section of the board.
Tip: If the unit lights on a fresh battery but won’t charge, suspect the charger section of the PCB. If it won’t transfer on outage, suspect the transfer relay or sense circuit on the emergency light control board.
Repair vs Replace (Decision Guide)
- Repair the board when the fixture is specialty (recessed, architectural, hazardous-rated) or integrated into finishes and you have an exact replacement PCB from the OEM.
- Replace the unit when the housing is standard thermoplastic/steel, the PCB is obsolete, or battery + labor + board approaches the cost of a new UL 924 unit.
- Consider self-testing for replacements—automated monthly/annual checks reduce future labor.
Budget tip: If three or more components are questionable (battery, board, heads), a new unit is often cheaper and more reliable long term than chasing a hard-to-find replacement emergency light circuit board. See Emergency Lights.
Compatibility & Parts Matching
- Match the manufacturer/series and revision of the board; avoid “near” matches.
- Verify battery chemistry/voltage supported by the board (SLA/Ni-Cd/LiFePO4 as listed).
- Confirm lamp load (wattage) and remote-head voltage (6 V/12 V) if the unit is remote-capable.
- Cross-check any fuses, thermistors, or NTCs on the BOM if supplied separately.
- For low-voltage systems, make sure a 6v emergency light circuit board is only used with 6 V batteries/heads, and a 12v emergency light circuit board is only used with 12 V batteries/heads—never mix 6 V and 12 V parts on the same emergency light board.
Safety, Warranty & Compliance Notes
- UL Listing: swapping non-listed boards can void the unit’s listing—stick to OEM parts for that model, especially on exit sign/emergency light combos where the exit sign emergency light circuit board is part of the listing.
- ESD & PPE: protect the PCB from static; use eye protection and follow lockout/tagout.
- Records: document serial numbers, part numbers, and work performed for your inspection file.
After-Repair Tests & AHJ Packet
- Perform a push-to-test check (30 seconds) on AC power.
- Run a full 90-minute discharge and verify lamp output stays adequate to the end.
- Log pass/fail, any corrective actions, and date labels inside the housing.
- Add photos of aimed heads along the egress path to your packet.
This gives your AHJ a clear trail showing when the emergency light circuit board was replaced or serviced and that the unit still meets UL 924 runtime.
FAQ
Can I use a “universal” board from another model?
Not recommended. Boards are tuned for specific batteries/LED loads. Use the OEM emergency light circuit board listed for your unit to preserve UL 924 compliance.
My unit charges but fails the 90-minute test—board or battery?
Swap in a known-good battery first. If runtime still fails, check lamp load and then suspect the driver/board. A weak battery will sag early; a failing emergency light board may shut down or under-drive LEDs even with a good pack.
How do self-testing units change repairs?
They add diagnostics (blink codes, logs) that speed triage, but the board is still the charger/transfer/driver. Replace like-for-like and clear faults after testing.
What’s the difference between a 6v and 12v emergency light circuit board?
A 6v emergency light circuit board is designed for 6 V batteries and heads, while a 12v emergency light circuit board is designed for 12 V systems and often supports longer runs or higher remote loads. The components, trace spacing, and driver circuits are optimized for that voltage—never mix them in the same fixture.