LiftMaster / Chamberlain4-6 or blinking green receiving LED
Chamberlain Group maps these states to safety sensors that are obstructed or not aligned.
Cross-brand failure family
Safety Beam Obstruction, Alignment & Interference
Use this family when the opener's safety-beam system is powered but the beam is blocked, misaligned or disturbed by interference.
CROSS-BRAND QUICK ANSWERVerified September 2, 2026
Across Chamberlain/LiftMaster and Genie systems, a powered safety-beam circuit can still stop closing when the beam is obstructed, the photo eyes lose alignment or the receiving side is disturbed. The exact LED or code is brand-specific, but the first job is the same: preserve the safety system, read both indicators and verify the beam path before replacing electronics.
Manufacturer signals
Same family, different language.
Do not translate one brand's blink count into another brand's code. Use the exact signal first, then the normalized family.
LiftMaster / Chamberlain1-1
The official code includes blocked, misaligned, disconnected or wiring-related sensor faults, so use LED state to split beam-path from circuit faults.
Genie Safe-T-Beam2 red blinks + green ON
Genie lists beam misalignment, obstruction or a defective sensor for this pattern.
Genie Safe-T-Beam3 red blinks + green ON
Genie identifies receiver interference; direct sunlight is one documented example when no physical obstruction is present.
LiftMaster / Chamberlain1-4
Chamberlain Group defines 1-4 as a safety-sensor obstruction or misalignment lasting less than four seconds; momentary beam crossings can be normal while a flickering receiver points to marginal alignment.
Genie Excelerator5 powerhead blinks
Genie defines five repeating Excelerator status-light blinks as a Safe-T-Beam malfunction; use the separate red/green sensor chart to split beam-path from circuit faults.
Marantec SynergyCode 15
Marantec's Synergy troubleshooting table maps code 15 to photo-eye connection/alignment or a blocked beam, so keep obstruction/alignment and circuit checks separate until the visible sensor state is known.
Marantec M55Code 15
The exact M55 table also maps code 15 to photo-eye connection, alignment or beam obstruction, but the M55 remains a separate diagnostic family because its overall numeric code set differs from Synergy.
Craftsman 139.53918D4 Learn-LED flashes
The exact Sears REV F chart maps four flashes to slight safety-sensor misalignment, with the receiving indicator dim or flashing.
Linear LDO33/LDO503 lamp flashes
The shared LDO33/LDO50 table maps three flashes to a safety-beam obstacle. Keep that model-family lock before using the count because later Linear generations remap other values.
Check first
Low-risk discriminators
- Remove objects, cobwebs and debris from the beam path without bypassing either sensor.
- Read both sensor indicators together; one light by itself is not enough to translate the condition.
- Watch whether the LED state changes when the door vibrates or when direct sunlight reaches the receiver.
- After correction, perform the manufacturer's safety-reversal test rather than assuming a steady LED proves the system is safe.
Evidence against
What makes this family less consistent
- Both sensor LEDs remain in the manufacturer's normal solid state throughout the failed close cycle.
- The door reverses only after firmly contacting the floor, which makes DOWN-travel setup more relevant.
- The door is heavy, crooked or binds when disconnected from the opener, which moves the diagnosis toward the mechanical/force family.
Take the next diagnostic action.
Stop DIY here
- The door is off-track, heavy or has damaged spring/cable hardware.
- Sensor brackets or low-voltage wiring are damaged beyond an accessible inspection.
- The correct beam state cannot be restored after alignment and obstruction checks.