KX-T7440CB, KX-T7440C - Panasonic PBX Service Manual (repair manual). Page 13

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13
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KX-T7440C/KX-T7440C-B
TROUBLESHOOTING GUIDE
1. NO OPERATION
2. LED DOES NOT LIGHT
Is the handset of the DSHS proprietary
telephone off-hook?
Bring the handset to an off-hook
status.
NO
YES
Does an oscillation signal (4MHz)
appear at pin  4  (OSC2) of IC3?
Does pulse signal appear at pin 12 
and 18 of IC3?
Check Q1
∼
Q41
Is the extension use?
Check data communication circuit.
Bring the extension to an use status.
Check X1, IC1, IC4, R138 and R139.
YES
YES
NO
NO
NO
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