Lamp; Ptc And Ptc Protector - Samsung SR-L676EV Service Manual

1) Power circuit
PCB sub ass'y (Inverter PCB) is activated with AC POWER input when the refrigerator door is open
and R-lamp relay(RY05) is activated. If the AC POWER is supplied to the power block, the smooth
capacitor(C3) gets around VOLTAGE DC(VOLTAGE AC X 2) AC POWER through rectification.

2) Lamp

If power is supplied to the PCB sub ass'y, diac(DB4) is activated. When C4 is over 35C/DC, voltage
is supplied to TR Q2 base by the continuity of diac. Then, TR Q2 is activated.
When TR Q2 is activated, current flows to C5 – C6 – CH1 – PT1 – R9. At that time, current flows to
PT2 and PT3.
If the discharge of capacitor C6 is completed, reverse current flows to PT2 and PT3 and TR Q2 turns
off TR Q3 turns on. The current flows to PT1 – CH1 – C6 – C5 – C8.
Lamp light up by the repetition of TR Q2, Q3 on/off. Its frequency range is 30~40KHz during
on/off.

3) PTC and PTC protector

PTC is designed to smooth the lighting and to lengthen lamp's life by heating filament of lamp. The
PTC protector prevents damage from PTC by cutting off power through triac if filament emits high
voltage at the beginning of lighting.
To check the PTC, measure resistance (150Ω ± 25% is normal). But, PTC resistance can be challged by
the ambient temperature and PTC operation. The above resistance value is counted in 20 sec after
lamp is off with the temperature 25˚C.
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