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3. Troubleshooting
Because of the high complexity of the circuitry used in the
amplifiers covered by this manual, most, if not all, of your
troubleshooting efforts will be at board level. Proper component-
level troubleshooting and service will also usually require
specialized test fixtures that may not be economically sensible to
have unless you do a high volume of service work on these
amplifiers. See the Servicing chapter of this manual for informa-
tion on these fixtures.
3.1 Initial check
When first checking the operation of a suspect amplifier on the
bench, always turn your variable transformer down to zero before
plugging the amplifier in. After you turn the amplifier on, gradually
turn up the AC voltage as you observe the amplifier's behavior and
its current draw; this will help you determine what, if anything, is
wrong with it. If you see or smell smoke, flames, or any other signs
of short circuits or excessive current draw, quickly turn the AC back
down to zero. If no such problems occur, it is usually safe to turn the
AC up to the amplifier's full operating voltage for further testing.
The following procedure will help you determine if the amplifier
has a problem and if so, where it may be located.
Starting at zero volts
1.
Start with the variable transformer at zero.
2.
Connect an AC voltmeter to monitor the transformer output
and an AC ammeter to monitor the current delivered to the
amplifier.
3.
Connect the amplifier to the output of the variable trans-
former.
4.
Turn on the amplifier.
LED activity starts
5.
Gradually turn up the AC voltage. When it reaches about 25%
of the amplifier's operating voltage (30 volts for a 120-volt
model or 60 volts for a 230-volt model), the power LEDs on
both channels should start to flicker. By the time it reaches
about 40% (50 volts for a 120-volt model or 100 volts for a
230-volt model), both power LEDs and both protect LEDs
should be on.
6.
Continue increasing the AC voltage. When it reaches about 70
volts (120-volt model) or 140 volts (230-volt model), both
protect LEDs should go out and all four fans should start up.
Check current draw
7.
At this point, the current draw for a PowerLight 6.0
PowerLight 6.0 II should be about 2 A or less for a 120-volt
model or 1 A or less for a 230-volt one. For a PowerLight
9.0
PFC
, it should be about 2.5 A or less (120-volt model) or 1.25
A or less (230-volt model).
Technical Service Manual
PowerLight 6.0 II, PowerLight 6.0
PFC
PFC
PFC
, and PowerLight 9.0
8.
If all is well, you can safely increase the AC voltage to the
amplifier's normal operating level and test its audio perfor-
mance. Once the AC voltage is at full, the amplifier should
behave normally. On the left side of the front panel, the two
power LEDs should be lit, while the standby and protect LEDs
should not. On the right, the signal, -20 dB, -10 dB, and clip
LEDs should light only in response to an output signal. If they
do not, continue by following the preliminary troubleshooting
guide.
3.2 Preliminary troubleshooting
Abnormal behavior of the amplifier indicates some problem in one
or more of its parts. You can use the observed patterns of this
behavior to help deduce where the problem lies. The amplifier has
two channels with independent power supplies; a defect may exist
on one channel that does not affect the other.
Power, Standby, and Protect LEDs: None lit on one
or both channels
•
The main fuse for the affected channel(s) may be blown. The
main fuses are located in the line filter assembly and are
accessible when the amplifier's top cover is removed.
•
The audio module's housekeeping supply is not working on the
affect channel(s). This is a rare failure because the house-
keeping supply has very reliable protection against short
circuits and other possibly destructive situations. Without its
housekeeping supply, though, the audio module cannot signal
the power supply module to turn on.
Protect LED lit
•
If the Protect LED lights steadily, without interruption, the
power supply module is not working.
•
If the amplifier is hot, it has probably overheated and will stay
in protect until it cools down to a safe temperature.
Amplifier endlessly cycles on, into protect, and
then off, and over again
•
There is a defect in the audio module—probably in the output
circuitry—that prevents the power supply module, as it starts
up, from reaching its proper rail voltages or places DC on the
output. When this happens the channel immediately switches
into protect, and then the power supply resets and tries to
start again.
or
23
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Table of Contents
Troubleshooting
