Transcript TROUBLESHOOTING

TROUBLESHOOTING IN PA
SYSTEM
Introduction
• Troubleshooting is a form of problem solving,
often applied to repair failed product or
processes.
• It is a logical, systematic search for the source of
a problem in order to solve it, and so the product
or processes can be made operational again.
• It is needed to develop and maintain complex
sysytems where the symptoms of a problem can
have many possible causes.
Troubleshooting in PA systems
• A public address system (PA system) is an
electronic sound amplification and
distribution system with a microphone,
amplifier and loudspeaker, used to allow a
person to address a large public.
• There are plenty of oppportunities for
something to go wrong; leads can get pulled
loose, batteries can die unexpectedly and
amplifiers can overheat and shut down.
Look for common explanations first
1. The signal lead isn’t plugged in, or has pulled
free or is connected in the wrong place.
2. Something in the signal path has no power.
3. Gain is too low.
4. A cable is faulty.
5. Equipment has failed.
Flow Chart for troubleshooting in PA equipment.
Troubleshooting Techniques
• Symptom: No sound output from loudspeaker,
no click, no hum or hissing sound. Set
completely dead. No voltage.
• Likely fault: Set is not getting power supply.
Fuse might have blow off or main plug
disconnected or power supply unit defective.
• Remedy: Check the mains line and power
supply unit to locate the fault, rectify the fault.
• Symptom: Resistance and DC voltage
measurement inside the set normal but
no hissing noise or single output.
• Likely fault: Loudspeaker leads might have
become short circuited or broken or
loudspeaker coil short.
• Remedy: Check the short of resistance
measurement and check the feeder by
capacitance measurement.
• Symptom: Noise present but no signal
output . Resistance and DC voltage are
alright.
• Likely fault: The presence of noise shows
that the pre-amplifier and other stages are
alright. Hence microphine lead open or
shorted to shield.
• Remedy: Check by meter and rectify the
fault.
• Symptom: Power supply transformer
getting overheated.
• Likely fault: Short circuit in the power
supply unit or some stage short
circuiting the power supply line.
• Remedy: Check the divergent circuits by
isolation method and locate and
remove the fault.
• Symptom: No sound in one LS , normal
sound in other speakers.
• Likely fault: Speakers defective,or the
fault is loudspeaker lead or connector.
• Remedy: Check the loudspeaker circuit by
resistance measurement and remove the
fault.
• Symptom: Excessive hum.
• Likely fault: Inadequate filtering in the
power supply due to open or leaky capacitor
of a filter circuit. Ripple picked by base
circuit of an amplifier stage. Coupling of
mains leads with microphone leads or the
matching transformer near AC loads or near
AC transformer.
• Remedy: Put a good capacitor across the
filter capacitor if hum is removed, the filter
capacitor is removed, repace it.
• Symptom: Excessive distortion
• Likely fault: Positive feedback causing high
pitched whistle. Sometimes the o/p may be
supersonic, it will overload the amplifier
and cause distortion.
• Remedy: Check the source of distortion by
short circuiting i/p of stages one by one and
thus identify the defective stage and rectify
it.
THANK YOU