— 5 —
Power Amplifier (LA4598)
The power amplifier is a 2-channel power amplifier with a standby switch.
The following table shows the pin functions of the power amplifier.
TROUBLESHOOTING
Nature of Trouble
Faulty Block
Checkpoint
No power
Power Supply Circuit
Emitter of T2 should p5.5 V.
Base of T2 should r6 V.
Power Jack
Jack contact.
No sound at all
Power Amp. (LA4598)
Pin 9 should r9 V when the
power switch is turned on.
Check output signals of pins 3 and 12.
CPU (MSM6387-13)
Pins 21 ~ 30 should provide pulses.
Pin 5 should have a sound signal when
keys are pressed.
Oscillator
Pins 8 and 9 of the CPU should receive
an ocsillation signal.
A certain key or switch
does not function
Key and Switch Matrix
Dust on the contact.
Certain keys or switches
do not function
Key and Switch Matrix
Open circuit on KC or KI line.
Pin No.
Terminal
In/Out
Functiion
1
Power GND
Ground (0 V) source
2
Ch1 B.S.
Out
Terminal for a bootstrap capacitor
3
Ch1 OUT
In
Channel1 output
4
VCC
In
+9 V source. Connected to the power source directly.
5
Ch1 N.F.
In
Negative feedback input
6
Ch1 IN
In
Channel1 input
7
D.C.
Terminal for a decoupling capacitor
8
Pre GND
In
Ground (0 V) source
9
Standby
In
Power control signal input. 0 V: OFF, +9 V: ON
10
Ch2 IN
In
Channel2 input
11
Ch2 N.F.
In
Negative feedback input
12
Ch2 OUT
Out
Channel2 output
13
Ch2 B.S.
Terminal for a bootstrap capacitor
14
NC
Not used.
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