Troubleshooting - Casio PK-5 Service Manual

Amplifier/Voltage Regulator (IC1: AN8053N)
Consisting of an amplifier and a voltage regulator, AN8053N amplifies the sound signal from the CPU and
also provides the CPU +5V source.
The following figure shows the internal block diagram of IC1.
Nature of Trouble
No sound at all
Certain key(s) or
switch(es) do(es) not
work.
5V
VCC NC CONT VREG
16 15 14 13
5V REG
POWER
1 4
2 3
SPO NC SP GND PC-1

TROUBLESHOOTING

Faulty Block
Power amp.
(IC: AN8053N)
Power Switch
CPU
(LSI1: MSM6387-03)
Oscillator (X1)
Key or Switch Contact
Open Circuit on KO or KI
Lines
NC NC NC PRE GND
12 11 10
-
SP AMP
VREF
+
5 6
7
PC-2 SPI SPM
Pin 13 should have +5 V.
An amplified waveform should be observed at pin
1.
Voltage at pin 3 of the CPU should be raised from
0V to +5 V when the power switch is turned on.
Switch contact.
Pins 24 ~ 30 should provide pulses.
Pin 5 should provide a sound waveform when a
key is pressed.
Pins 8 and 9 of the CPU should receive an oscil-
lation signal.
— 4 —
9
8
VREF
Checkpoint