Troubleshooting - Casio CTK-480 Service Manual

INITIAL RESET CIRCUIT
When batteries are set or an AC adapter is connected, the reset IC provides a low pulse to the CPU.
The CPU then initializes its internal circuit.
Reset IC
RE5VA35A
Nature of Trouble
No power
No sound at all
Certain keys or switches
do not function
A certain key or switch
does not function
Battery Set
VDD
IC102

TROUBLESHOOTING

Faulty Block
Power supply circuit
Power switch
Power jack (J101)
Power Amp (IC101: LA4596)
CPU (LSI101: MSM6755B-06)
Oscillator
Key and switch matrix
CPU (LSI101: MSM6755B-06)
Key and switch matrix
CPU
MSM 6755B-06
LSI101
RESET
Faulty IC101. Replace IC101.
Faulty D106 ~ D109. Replace D106 ~
D109.
Faulty Q101 ~ Q104. Replace Q101 ~
Q104.
Poor contact. Clean the contacts.
Open J101 or poor soldering. Replace
J101 or resolder.
Open or shorted IC101. Replace IC101.
Faulty LSI101. Replace LSI101.
Faulty Q111. Replace Q111.
Open X101. Replace X101.
Open circuit on KO or KI line.
Replace keyboard PCB assembly.
Faulty LSI101. Replace LSI101.
Dust on the contact.
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Cause/Remedy