Panasonic EASA-PHONE KX-T2355 Service Manual And Technical Manual page 14

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—«KX-T2355
g TONE DETECTION CIRCUIT
Function:
This circuit is used to sense the status of the line (busy tone or dial pone Sung Auto PAUSE or Auto Redial.
Circuit Description:
The signal from the line passes through the path D6—> Q1—> R11— R59— C42-—> C48, and is then input to pin 2 of IC4.
Here the dial tone or busy tone alone is extracted and output from pin 1 of IC4. It is then input to pin 6 of IC4 and compared
with the level at pin 5 of IC4. When a busy tone or dial tone is input, pin 7 of IC4 becomes HIGH logic level. This level
passes through D15, and is smoothed by C55— Q14 goes ON collector of Q14 becomes LOW logic level as 12 of IC1
becomes LOW logic level.
When there is not busy tone or dial tone, pin 7 of IC4 becomes LOW vale level p23 ale cae OFF collector of ac
becomes HIGH logic level> pin 12 of IC1 becomes HIGH logic level. :
Timing Chart
Pin 5 of 06 I 1 i] ) iil | i — f i Collector of G14
Pin 7 of IC4 |} |
1. UNIT DOES NOT TURN ON
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Insert the three
batteries.
Connect the
handset and place
it on-hook.
Set the Volume
Control to MAX.
the telephone line.
"Operate the On/Off
Switch to turn the.
power on. : a
-{s the voltage at —
Connect the unit to |
Does the On/Off
~ indicator light?)
-Pin 18 of IC2 ata —
— low logic level?
| Is the voltage at |
Pin 42 of IC1 5 V?
Is there oscillation at
Pin 32 of IC1?
'Check $4, Q7, R8,
Q1, Q2 and D29.
TROUBLE SHOOTING GUIDE
- Check Q1, Q2, Q3,
D6, D11 and D12.
Is the voltage at
Pin 34 of IC1 ata
high logic level?
Check IC1.
(Next Page)
D19.
Check Q15,
D20, D21 and