Panasonic KX-FT21BX Service Manual page 99

(1) Defective ITS (Integrated telephone system) section
1 No handset and monitor transmission/reception
Following the ITS section or NCU section, search for the route between the microphone and
the telephone line (sending) or between the telephone line and the speaker (receiving) where the signal disappears.
Check the components at that point.
2 No pulse dialing
Does pin 99 of IC1 on
the digital board change
from high to low level?
YES
Does the base Q3 on the
analog board change from
high to low level?
YES
Check RLY1 on the analog
board.
3 No ring tone
With the unit on-hook (standby),
does a bell ring when pins 3-4
of PC1 on the analog board
are shorted?
YES
Check the bell detect circuit
(R37, C35, PC1, etc.)
on the analog board.
4 No tone dialing
Check that the DTMF signal is
being output from pin 3 of IC5
on the digital board.
YES
Check that the DTMF signal is
being output at the points on the
DTMF circuit send route.
NO NO
Replace Q3.
Check the conduction between the base
NO
of Q3 on the analog board and pin
99 of IC1 on the digital board.
Is a current flowing between pin 4
NO
of PC1 on the analog board and
pin 56 of IC1 on the digital board?
YES
Check the path over which the
bell signal is sent to the speaker.
NO
Check IC5 and pin 70~81 of
IC1 on the digital board.
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Does pin 99 of IC1 on the
digital board change from
high to low level?
NO
KX-FT21LA
NO
Check IC1 on the
digital board.
Check the path between pin 4
of PC6 and pin 19 of IC4.