One zone dead, or amplifier in protect

Likely causes

• Amplifier in protect: a short or near-short on the speaker line, or a load below the amplifier's rated minimum

  ~25%

  Protect LED on, and the amplifier comes back the moment you disconnect that speaker line and re-power it. Reconnect the line and it trips again, repeatably. The amplifier is not broken; it is defending itself.

• Thermal shutdown: blocked rack ventilation, sustained high level, or a marginal load

  ~18%

  Works cold, drops out thirty to sixty minutes in, comes back after it cools. Rack air is hot and the amplifier's own temperature reporting confirms it.

• Open line: broken splice, failed transformer tap, a driver's lead off

  ~18%

  An impedance meter reads open or far too high at the amplifier end, and when you count the working speakers the zone is short of its tap total.

• Distributed-line taps exceeding the amplifier's output, or taps changed during a fit-out

  ~12%

  The zone worked until someone added speakers or turned taps up. Measured load is well below what the amplifier is rated to drive, and it trips at level rather than at idle.

• Source, routing or mute: DSP mute, wrong output, paging priority latched, control system holding the zone off

  ~12%

  No signal at the amplifier input at all. The DSP output meter for that zone is dead while the others move, or a paging or emergency priority is still asserted from earlier in the day.

• Failed amplifier channel or power supply

  ~8%

  Move the zone's line to a known-good channel and it plays. Put a known-good zone on the suspect channel and it does not.

• Wrong wiring for the amplifier mode: low-impedance speakers on a constant-voltage line or the reverse, or the output mode switch set wrong

  ~5%

  Very quiet and thin, or instant protect at the first bit of level. Check the amplifier's output mode switch against what is actually hanging on the line.

• Speaker itself failed

  ~2%

  One driver dead in an otherwise healthy zone, measured load only slightly off. Rare, and almost never the whole zone.

What to bring

• impedance or load meter for distributed lines
• DSP configuration software
• as-built and tap schedule
• known-good amplifier channel or spare amplifier
• multimeter
• IR thermometer
• punch-down and splice kit

Steps

1. 1

   Step 1: Prove signal actually reaches the amplifier input

   Watch the DSP output meter for that zone, then listen or meter at the amplifier input itself. Nothing arriving means the fault is upstream (mute, route, control state or a latched paging priority) and you can stop thinking about speakers entirely.

   If that doesn’t do it

   Signal present at the amplifier input and nothing out: go to protect and the line.

2. 2

   Step 2: Disconnect the speaker line at the amplifier and re-power

   Amplifier comes out of protect and stays out with the line off, the fault is in the line or the load. It stays in protect with nothing connected and the amplifier itself is the fault. This is the one move that decides which half of the system you are working on.

   If that doesn’t do it

   Amplifier still in protect with the line disconnected: swap the channel, then the amplifier.

3. 3

   Step 3: Measure the line properly, with the amplifier off and the line disconnected

   Use an impedance or load meter at the amplifier end and compare the reading against the expected load for the tap total in the as-built. Open, short, and far-too-low each send you somewhere different: open is a break or a failed tap, short is damage or a crushed cable, too low is too many taps or the wrong tap settings.

   If that doesn’t do it

   Measured load matches the design and the amplifier still trips: go to thermal and to the amplifier itself.

4. 4

   Step 4: Halve the zone

   Disconnect at the midpoint splice and measure each half. Take the bad half and halve it again. Four or five moves finds the fault on a long run instead of visiting every speaker in the building. This is the method, and it is worth doing properly with the as-built in your hand.

   If that doesn’t do it

   Both halves measure correct in isolation but the whole line is wrong: the fault is at the junction you opened. Look there.

5. 5

   Step 5: Add up the taps against the amplifier and check the output mode

   Total every tap setting in the zone and compare it against the amplifier's rated output with design headroom left over. Then confirm the amplifier's output mode matches the line: constant-voltage against constant-voltage, low-impedance against low-impedance. A mode switch in the wrong position will trip an amplifier instantly or leave a zone inexplicably thin.

   If that doesn’t do it

   Taps and mode correct: go to thermal.

6. 6

   Step 6: Check thermal honestly

   Rack airflow front to back, clean filters, no blocked vents, nothing stacked on the amplifier, and read the unit's own temperature reporting during a run. A zone that dies an hour in and recovers cold is thermal or a marginal load; it is never a signal fault, so stop testing the signal.

   If that doesn’t do it

   Rack runs cool and it still drops out at time: the load is marginal. Re-measure at level, not at idle.

7. 7

   Step 7: Substitute the amplifier channel

   Move the zone to a known-good channel on the same amplifier or a spare. Zone plays on another channel means the channel is dead. Zone still dead on a proven channel means line or speakers, and you have eliminated the most expensive part.

   If that doesn’t do it

   Zone is dead on every channel and the line measures correct: check the line's polarity and continuity end to end before you replace anything.

8. 8

   Step 8: Record the measured load and the tap list in the room file

   Measured impedance per zone, tap settings per speaker, and load per amplifier channel with the headroom you left. The next person to add a speaker needs that number, and its absence is why this zone failed.

   If that doesn’t do it

   No as-built exists: make one for this zone before you leave. It is an hour now and a day later.

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