Failure Diagnosis Of The Power Amp Block - Pioneer VSX-AX4AVi-S Service Manual

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7.1.11 FAILURE DIAGNOSIS OF THE POWER AMP BLOCK

If "AMP ERR" flashes on the FL display immediately after the
power is turned on, then the unit is shut down, the power
A
amplifier block is damaged, and DC voltage is output. In this
case, either or both of the current and voltage amplifier block(s)
is(are) damaged. Herein is described how to diagnose which
block is in failure.
Most cases of damage in the power amplifier block are damage
on the power transistor caused by excess power consumption,
such as short-circuiting of the speaker terminals and use of low-
impedance speakers that are not guaranteed. The failure diagnosis
is therefore conducted on the current amplifier block first, then
on the voltage amplifier block.
B
Voltage amplifier block
INPUT
C
D
Notes:
• During diagnosis of the amplifier block with the power on, if
you touch a high-impedance circuit (in particular, both ends of
100-ohm base resistance of the power transistor) with the probe
of an oscilloscope or a tester, the circuit may be damaged by
oscillation of an oscilloscope or a tester.
• While a failure diagnosis is being conducted with the power on,
E
do NOT touch parts other than the power, input, and output
blocks.
• Only the points with CP (check point) marks in the schematic
diagram can be diagnosed while the power is on.
Operating temperature of the posistor assembling to the heat sink
No.
POS1L TH5001
PTFM04BH222Q2N34B0
POS1R TH5301
PTFM04BH222Q2N34B0
POS2 TH5002
PTFM04BD222Q2N34B0
F
* Operating temperature is body temperature of the posistor (the metal part).
238
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Current amplifier block
+VH
Power supply
resistor
+VL
Collector
resistor
Base
resistor
POWER
TRANSISTOR
(NPN)
POWER
TRANSISTOR
(PNP)
Base
resistor
Collector
resistor
-VL
Power supply
resistor
-VH
Operating
Part No.
temperature
60 ºC
60 ºC
100 ºC
VSX-AX4AVi-S
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1. Damage on the current amplifier block
Check of the power transistor and collector resistance
of each channel, using a tester
Tips:
In most cases where the current amplifier block is damaged by an
excess power consumption of the power transistor, damage is
caused by short-circuiting between the collector and emitter. The
collector resistor is open because of large collector current.
In this case, the channel in failure can be identified by checking
on which channel the resistance between C and E of the power
transistor is 0 Ω (some hundreds of ohms or less) and the resistor
of collector resistor is ∞ Ω. As a damage scar appears on the
surface of the part when the collector resistor is open, you can
also check it by visual inspection.
Note:
Even if the result of the measurement of resistance with the tester
shows that the power transistor is not short-circuited, that power
transistor may be damaged if the paired push-pull power
transistor has been damaged. Therefore, it is recommended to
replace both parts when either needs to be replaced.
2. Damage on the voltage amplifier block
Check of the base resistance (100 Ω) and Power supply
(±VH) resistor (4.7 Ω) of each channel, using a tester
Tips:
In most cases, the voltage amplifier block is damaged by
oscillation generated by a special load connection, a large-
amplitude output at higher frequencies out of the audible range,
OUTPUT
or an influence of damage on the current amplifier block (power
transistors). In many cases, the base resistance (100 Ω) is
damaged. It is necessary to check each part of the voltage
amplifier block, as damage may have been extended to other
parts.
In most cases, the resistors are open/damaged, or the transistors
or diodes are short-circuited/damaged.
• The resistors must not be open (the resistance must not be
higher than the indicated value).
• The terminals of transistors or diodes must not be short-
circuited (the resistance must not be extremely low).
(If the resistance is low but you are not sure if it is extremely
low, compare the value with that of the normal channel.)
If the voltage amplifier block is damaged, Power supply (±VH)
resistor (4.7 Ω) may also be damaged.
3. Other damage
Check of the bias protection diodes
Tips:
If the power amplifier is damaged, the bias protection diodes
may be deteriorated or open.
For a channel that has been diagnosed to be in failure, the Vf
(forward descending voltage) of the four diodes must be checked
to confirm that they are not deteriorated or open, using a tester,
after repair of the amplifier. If these diodes are deteriorated, its
distortion/frequency characteristics may be affected. If these
diodes are open, the scale of damage on the power transistors
may be extended if any abnormality is generated in the amplifier
next time.
Purpose
FAN control
FAN control
Detection of abnormal temperature
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Operation
FAN activation at more than 60 ºC
FAN activation at more than 60 ºC
OVERHEAT perform at more than 100 ºC
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