Reader dead: no light, no beep
very common
“Reader's completely dead. No light, no beep, nothing happens when I badge it.”
Likely causes
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No power or sagging power at the reader
~33%Meter at the reader terminals reads 0 V, or below the reader's rated minimum. Healthy voltage at the panel and much less at the reader means the drop is in the run, not the supply.
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Blown fuse or latched PTC on the reader's power output
~20%0 V at that output while the supply's other outputs are live. Drop the reader leg and a PTC output recovers on its own in a minute or two. That recovery is the signature, and it means overload downstream, not a dead board.
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Wiring fault: reversed polarity, open conductor, pinched at the hinge or the frame knockout
~19%Loop resistance on the power pair reads open or wildly high. Feed the reader from a fused bench lead at its rated voltage and it wakes up. That puts the fault on the run.
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Reader failed: surge, water in a mullion reader, condensation
~15%Known-good reader on the same wiring lights up. Water staining, a swollen face, or green corrosion on the pigtail confirms it.
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Reader powered but never polled: OSDP, or a Wiegand panel not driving the LED and buzzer lines
~13%Voltage measures good and the reader is dark or slow-blinking a fault pattern. An unpolled OSDP PD is routinely dark. Check the OEM LED chart and the panel's poll counters before you condemn power.
What to bring
- DMM
- Fused test leads
- Known-good reader
- Reader datasheet and LED chart
- Precision screwdriver set
- Headlamp
- Ladder for mullion and high mounts
Safety
Mullion and transom readers put you on a ladder with both hands busy. If the access supply shares an electrical room or sits beside a panelboard, you're there for the Class 2 side only. Stay out of the line side.
Steps
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Step 1: Badge it and watch the LED and sounder, but know which protocol you are standing at
On a Wiegand reader, dark and silent means power or the reader. On an OSDP reader, dark proves nothing: an unpolled PD sits dark or blinks a fault code. Check the OEM LED chart and the panel's polls for that address first.
If that doesn’t do it
OSDP with no polls showing: go to OSDP reader shows offline on the bus. Otherwise meter the reader terminals.
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Step 2: Read the reader's rated input off the label before you meter or feed anything
Input ranges vary hard by model. Wide-range readers tolerate well under 10 V, tightly specified 12 V readers do not, and 24 V and PoE-fed readers exist. The label or datasheet is the only answer. This is a lookup, not a memory item.
If that doesn’t do it
No legible label: get the part number and pull the sheet before you apply any source.
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Step 3: Measure Vdc at the reader terminals, not at the panel
12 V readers are commonly fed around 13.8 V from a battery-backed supply. Compare what you read against the rated minimum you just looked up. Below it, or 0 V, is your fault.
If that doesn’t do it
Voltage good? Jump to the reader swap and the polling check.
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Step 4: Check the output fuse or PTC at the supply or PDU
0 V out while the bus is healthy is a blown fuse or a latched PTC. Disconnect the reader leg and watch whether the output comes back on its own.
If that doesn’t do it
Output is live: chase voltage drop on the run.
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Step 5: Power the reader locally as a proof, at its rated voltage and polarity
Fused test leads from a source that matches the label, right at the reader. Wakes up = the run or the supply. Stays dark = the reader. Guessing 12 V at a 24 V or tightly specified reader is how you buy one.
If that doesn’t do it
Swap the reader.
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Step 6: Swap in a known-good reader on the same wiring
Free swap: do this before anything gets re-terminated. Good reader works = old one's dead. Both dead = wiring or host.
If that doesn’t do it
Verify the reader is being polled.
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Step 7: Confirm the panel is actually polling it
On Wiegand the panel usually drives the LED and buzzer lines: no drive, no life. On OSDP, read the per-address poll and response counts.
If that doesn’t do it
Go to OSDP reader shows offline on the bus or Intermittent reads and ghost reads on Wiegand.
References
- UL 294
- SIA AC-01: the de facto description of the Wiegand reader interface; verify its current standards status, as it is widely reported withdrawn and superseded in SIA's direction by OSDP
- IEC 60839-11-5 (OSDP)
- NFPA 70 Art. 725: Class 2 power-limited circuits (cable material moved to Art. 722 in the 2023 edition; verify your adopted edition)