Pioneer VSX-94TXH Service Manual page 67

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5.1.5 FAILURE DIAGNOSIS OF THE POWER AMP BLOCK
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If "AMP ERR" flashes on the FL display immediately after
the power is turned on, then the unit is shut down, the
power 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.
Voltage amplifier block
INPUT
TE
L 13942296513
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, 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.
www
Operating temperature of the posistor assembling to the heat sink
No.
POS1L TH5001 PTFM04BC222Q2N34B0
.
POS1R TH5301 PTFM04BC222Q2N34B0
POS2 TH5002
* Operating temperature is body temperature of the posistor (the metal part).
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Current amplifier block
+VH
Power supply
resistor
+VL
Collector
resistor
Base
resistor
POWER
TRANSISTOR
(NPN)
Base
resistor
Collector
resistor
-VL
Power supply
resistor
-VH
Operating
Part No.
x ao u163
temperature
y
105 °C
i
105 °C
– –
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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
Q Q
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damaged. It is necessary to check each part of the voltage
POWER
TRANSISTOR
amplifier block, as damage may have been extended to other
(PNP)
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
co
Detection of abnormal temperature OVERHEAT perform at more than 105 °C
.
Detection of abnormal temperature OVERHEAT perform at more than 105 °C
–
VSX-94TXH
7
9 4 2 8
0 5 8 2 9 9 4 2 8
m
Operation
–
7
8
9 9
A
B
C
9 9
D
E
F
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