Lanzar OPTI2000D - Manual (Page 13)

Check for shorts on speaker leads.
Check that the volume control on the head unit is turned down low.
Remove speaker leads, and reset the amplifier. If the Protection LED still comes
on, then the amplifier is faulty.
Check that the minimum speaker impedance for that model is correct.
Check for speaker shorts.
Check that there is good airflow around the amplifier. In some applications, an
external cooling fan may be required.
Check that the Level control(s) is set to match the signal level of the head unit.
Check that all crossover frequencies have been properly set.
Check for shorts on the speaker leads.
This is always caused by a poorly-grounded RCA patch cord.
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