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Emergency Light Circuit Board Instruction

Emergency Light Circuit Boards

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. 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.

Last updated: October 2025

Emergency Lights Emergency Lighting Guide Table of Contents

Troubleshooting Guide UL 924 • NFPA 101 For Facility Teams & Contractors

Overview: What the Board Does

Overview — What the Board Does: AC input (120/277 VAC) to charger; transfer sensing & relay switching to battery in <1 s; LED driver regulates lamp current for ≥90 minutes; status indicator and, on self-test models, fault logs/diagnostics.
The main PCB charges the battery, senses loss of AC and transfers to battery, regulates LED output for ≥90 minutes, and provides status/diagnostics.

The main circuit 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).
  • 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).
  • Status: provides indicator LEDs (and on self-test models, logs/diagnostics).

When these functions drift or fail, you’ll see dim/unstable lamps, blinking fault indicators, or batteries that never seem to charge.

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 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 board not regulating output correctly.

5-Minute Diagnostics (Safe & Simple)

Before opening the housing, de-energize the circuit and verify lockout/tagout as required. Then:

  1. Visual check: look for heat discoloration, swollen batteries, pinched wires, loose connectors.
  2. Verify AC input: confirm correct lead (120 vs 277 V) and tight neutral/ground. If a transfer device is used, verify its wiring.
  3. Battery test: measure open-circuit voltage; check age/date stamp. Swap in a known-good pack if available.
  4. Load sanity: sum the wattage of all lamp heads (on-board + remote). Compare to the unit’s 90-minute rating.
  5. Board connections: reseat low-voltage plugs; check fuses. Inspect for cracked solder joints near high-heat parts.

Tip: If the unit lights on a fresh battery but won’t charge, suspect the charger section of the board. If it won’t transfer on outage, suspect the transfer relay or sense circuit.

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. 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.

Safety, Warranty & Compliance Notes

  • UL Listing: swapping non-listed boards can void the unit’s listing—stick to OEM parts for that model.
  • 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

  1. Perform a push-to-test check (30 seconds) on AC power.
  2. Run a full 90-minute discharge and verify lamp output stays adequate to the end.
  3. Log pass/fail, any corrective actions, and date labels inside the housing.
  4. Add photos of aimed heads along the egress path to your packet.

FAQ

Can I use a “universal” board from another model?

Not recommended. Boards are tuned for specific batteries/LED loads. Use the OEM 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.

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.

Emergency Lights Emergency Lighting Guide