Valid read, door never unlocks

Likely causes

• Lock power path broken: relay contact, output fuse or PTC, no change at the lock during the strike window

  ~28%

  Meter across the lock leads while someone badges. On fail-secure hardware you want voltage to appear for the strike time; on fail-safe hardware you want it to disappear. Either change proves the controller did its job. No change at all is everything upstream of the lock.

• Dry-contact output with no power jumpered, or landed on the wrong contact

  ~18%

  Relay clicks and the output LED lights, but nothing changes at the lock. Measure across the contact, not through it: roughly source voltage across it at rest and near zero across it on grant means the contact is switching and there is no source behind it, or you are on the NC leg.

• Mechanical bind: strike keeper preloaded by a sagged door or racked frame, latch under pressure

  ~18%

  Strike buzzes or clicks on grant and the door still won't push. Pull the door toward you to relieve the preload and it opens. Preload ratings are per strike model. Look it up.

• Fail mode assumed instead of established

  ~15%

  You are at a maglock, a fail-safe strike or fail-safe trim, expecting voltage to appear. Meter at rest: voltage present at rest means fail-safe, and the grant is supposed to remove it. Steady voltage right through the grant window on a fail-safe door is the fault, not the healthy case.

• Wrong door or wrong output mapped in programming

  ~12%

  Live log shows granted on Door 3 while you're standing at Door 4, or the grant fires a relay on the other side of the panel. Mapping error, not hardware.

• Strike time set near zero, or unlock tied to the wrong condition

  ~9%

  A single fast tick at the lock and a clean grant in the log. Read the strike time: 0 or 1 s does exactly this.

What to bring

• DMM
• Jumper leads
• Laptop or panel keys with head-end access
• Allen and strike adjustment tools
• Feeler gauge
• Tape measure
• Lock datasheet

Steps

1. 1

   Step 1: Badge it with the live event log open

   Granted on the right door means credential, schedule and decision are all good and you're into wiring and hardware. Denied, invalid format, unknown card, or no event at all sends you somewhere else entirely.

   If that doesn’t do it

   Denied with the holder named? Go to Denied at certain times or certain doors. Invalid format or no event? Card works at one door, not another.

2. 2

   Step 2: Establish the door's fail mode before you interpret a single reading

   Meter the lock at rest, with nobody badging. Voltage present at rest = fail-safe (maglock, fail-safe strike or trim): the grant removes it. No voltage at rest = fail-secure: the grant applies it. Get this wrong and the next step tells you the exact opposite of the truth.

   If that doesn’t do it

   Can't tell? Read the hardware label and the door's intended mode, then go to Door won't release for egress, because a door in the wrong mode is a life-safety finding.

3. 3

   Step 3: Meter across the lock leads through the grant window

   Fail-secure: rated voltage should appear and hold for the programmed strike time, commonly 3 to 7 s. Fail-safe: voltage should drop to zero and stay there for that window. The change happening at all splits the whole tree: a change means lock or door, no change means relay or lock power.

   If that doesn’t do it

   It changed: go to the mechanical test.

4. 4

   Step 4: Confirm output type and the power jumper

   Dry contacts need a source brought to them; wet outputs are already fed. A clicking relay with nothing happening downstream is a missing jumper, a wrong COM/NO landing, or the NC leg. Test with voltage across the contact; only test continuity with the output de-energised and the source lifted.

   If that doesn’t do it

   Check the output fuse and supply under load.

5. 5

   Step 5: Check the lock output fuse or PTC and the supply under load

   Strikes and maglocks are typically a few hundred mA, but ELR exit devices, motorized locks and auto operators are a different class entirely: amps on the retract pulse, and often an inrush-rated supply. Every one of those figures comes off the hardware datasheet, never off a rule of thumb.

   If that doesn’t do it

   Supply collapses on operation: go to Reader resets when the lock pulls or Latch retraction and auto operator out of sequence.

6. 6

   Step 6: Command a momentary unlock from the head end

   That isolates reader and credential completely. Software unlock works but a badge doesn't = the read side or the decision. Neither works = output, wiring or lock.

   If that doesn’t do it

   Test the hardware mechanically.

7. 7

   Step 7: Test the hardware energised, loaded then unloaded

   Hold the door shut and try it, then relieve the pressure and try again. Opens only when unloaded = alignment, closer, or gasket. Fix the door or the strike position. Do not chase it with voltage.

   If that doesn’t do it

   Pull the lock and bench it, or condemn the hardware.

More Access Control guides

• Reader dead: no light, no beep
• Denied at certain times or certain doors
• Card works at one door, not another
• Nuisance door held and forced alarms
• Intermittent reads and ghost reads on Wiegand
• Read range short at one reader
• Keypad won't take the PIN

All 54 guides