Panasonic KX-FT21BX Service Manual page 67

4 The unit can copy, but cannot transmit/receive.
Connect the unit to the
loop simulator.
Switch : TX side T-R
Connect the oscilloscope.
Modem test start
(TEST CODE NO. 554)
Are four signals output
at the Tip-Ring?
NO
YES
Is the signal at pins
3 of IC5 output?
YES
NO
Check the solder at
pins 1~16 of IC5.
OK
Check the solder at
pins 70~81 of IC1.
OK
Replace IC5.
NG
Replace IC1.
- 41 -
Connect the PBX and
TEL. line and go off-hook.
Check the trace
NO
between pins 3 of
IC5 and Tip-Ring.
Check the trace
between T1 and pin
15 of IC5.
KX-FT21LA
Is the signal at pin 45
of IC5 dial tone input?
YES
Check the solder at
pins 1~16 of IC5.
OK
Check the solder at
pins 70~81 of IC1.
OK
Replace IC5.
NG
Replace IC1.