Panasonic KX-TDA0103X, Service Manual

Page: 43 / 178

8.2.1.6. Protection Circuit
This section explains about the Over Voltage Protection Circuit and Over Heat Protection Circuit and Battery Reverse
Connection Protection Circuit.
1) Abnormal Condition Detection Circuit
Abnormal condition detection circuit consists of thyristors Q524 and Q525 (on Sub board 2). When power supply operation
becomes abnormal, the abnormal detection signal is sent and Q524 and Q525 are turned ON. A current flows through the diode
of PC4, which is sent to the latch circuit of main converter, and the operation of main converter is stopped. (Refer to Main
Converter (P.33).)
Refer to Fig. 6 (D).
2) Over Heat Detection Circuit
When internal temperature of power supply rises abnormally, resistance values of thermistors NTC501 and NTC502 become
low, transistor Q590 (on Sub board 2) turns OFF, and voltage from pin 8 of IC301 is sent to the abnormal detection circuit.
Refer to Fig. 6 (A).
3) Battery Reverse Connection Protection Circuit
When the battery is connected to the unit in the wrong direction by mistake, the voltage of plus terminal becomes minus. Then
diodes D523, D524 and D525 turn ON. The transistor Q511 (on Sub board 2) turns ON, and the voltage from dropper circuit
(Refer to Alarm Signal Sending Circuit (P.42)) is sent to the abnormal detection circuit through zener diode D529 (on Sub
board 2).
Refer to Fig. 6 (B).
43
KX-TDA0103XJ / KX-TDA0104XJ / KX-TDA0108XJ / KX-TDA0103X / KX-TDA0104X / KX-TDA0108X