Casio SF-5500B Service Manual & Parts List page 16

Is Pin 1 of DET1 5.2 V?
Is Pin 11 of LSI1 sending the signal?
Is Pin 13 of LSI1 sending the signal?
Is the soldering of LSI2 or LSI3 poor?
Replace LSI1, LSI2.
No key input
START
Does the rubber key contact make positive
contact with the PCB assembly?
Is the soldering of LSI1 poor?
Replace LSI1.
1
Y
Y
Y
N
Y
N
— —
15
N
Replace DET1.
N
Replace LSI1.
N
Replace LSI1.
Y
Resolder.
N
Replace the rubber key contact.
Y
Resolder.