Troubleshooting - Casio CTK-485 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.
RN5VD40A
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
Reset IC
IC1

TROUBLESHOOTING

Faulty Block
Power supply circuit
Power switch
Power jack (J101)
Power Amp (IC101: LA4596)
CPU (LSI1: MSM6755B-17)
Oscillator
Key and switch matrix
CPU (LSI1: MSM6755B-17)
Key and switch matrix
CPU
MSM 6755B-17
LSI1
RESET
Faulty IC101. Replace IC101.
Faulty D104 ~ D106. Replace D104 ~
D106.
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 LSI1. Replace LSI1.
Faulty Q1. Replace Q1.
Open X1. Replace X1.
Open circuit on KO or KI line.Replace
keyboard PCB assembly.
Faulty LSI1. Replace LSI1.
Dust on the contact.
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Cause/Remedy