OPERATION CHECK-2
OUTPUT LEVEL & THERMAL DETECTION
TX-SR402/8240/HT-R420
RL6901
D6904
D6903
RL6902
POWER AMP.
PRI.
SEC1
Low
High
+B1
-B1
T901 MAIN
TRANSFORMER
Low
High
Q6303
THERMAL
SENSER
R6380
THERMAL
DETECTION
OUTPUT
LEVEL
DETECTION
VOLH/
THPRO
Q7008 MAIN
MICROPROCESSROR
Q6303
SEC1H
23
2
SPEAKER
OUT
F6901
F6902
Low-voltage
<Block diagram>
TX-SR402
/8240
HT-R420
HIGH
MODE
LOW
MODE
+/- 52.0 V
+/- 28.4 V
+/- 63.0 V
+/- 29.0 V
High-voltage
Regarding the power supply system of this unit.
<Function>
1. High-voltage mode
Usually, the power supply supplies high voltage to the power amplifier circuit when the relay(RL6901) is turned on.
2. Low-voltage mode
When as follows, a power supply changes to the state of supplying low voltage when the relay (RL6901) in turned off.
(1) Excessive output signal is continuously outputted from power amplifier.
(2) Temperature of a heat sink surpasses 80 degrees.
<Purpose>
1. The loss which power amplifier generates is decreased. As a result, the miniaturization of a heat sink is realized.
2. Corresponds to a safety standard.
<Necessity for a check of operation>
May not notice the fuse (F6901, F6902) broken in the case of repair.
Because the power supply is continuing supplying voltage from the High side of SEC1 at high-voltage mode.
When a power supply Ccircuit changes to low voltage mode, amplifier does not operate.
Therefore, it is very important to check operation of this power supply system containing a fuse.
<Procedure>
[NOTE2]
Don't connect speakers or any load. Don't short speaker terminals.
(1) Set the unit is Multi channel input state.
(2) Set the master volume into the minimum.
(3) Apply sine wave signal to MULTI CHANNEL INPUT (FL+FR+C+SL) terminals.
(4) Connect an oscilloscope to speaker terminal of FL channel.
(5) Adjust master volume so that a speaker output may become distortion about 5%.
(6) Check that the RL6901 is turned off after about 5 seconds.
And the power supply changes to low-voltage mode.
(7) Adjust the master volume so that output voltage may become half.
(8) Check that the RL6901 is turned ON after 2 to 3 minutes.
And the power supply returns to high-voltage mode.
