Sam4s ER-280 SERIES, Service Manual, Page: 35 / 88

5. Troubleshooting
SAM4S ER-280 SERIES 5-5
End
Key Board Problem
Key Input
Failure ?
Y
N
1. Check the Key Scan Part 74HC138(U19)
2. Check the Key Return part 74HCT541(U21)
3. Check the related Circuit and Pattern
4. Check & Change Key Board Assy
5. Check the KBD Connector on PBA
Specific Key
Failure?
1. Check the affected Key
2. Check the Matrix Bus & Data Bus
3. Check the Diodes(BAT43WS *7EA)
4. Check the Key Board Assy
N
Mode Key
Ok?
Y
Y
1. Check the Mode Key Assy
2. Check the Diode (D19)
3. Check the 74HC138(U19) & Data Bus
N
5-5 Key Board Problem