LG GR-J303TG, Service Manual

Page: 15 / 46

3-2. EXPLANATION OF CIRCUITS
3-2-1. POWER CIRCUIT
Power circuits consist of SMPS (Switching Mode Power Supply) power, and the SMPS consists of the rectification part
(BD1, CE1) to convert AC voltage to DC voltage, the switching part (IC3) to switch the converted DC voltage, a transformer
to transfer energy of the primary side on the switching terminal, secondary side power to supply power to the MICOM and
IC and the feed back part (IC4, IC5) to feedback the secondary side voltage to the primary side of transformer in order to
maintain it uniformly.
Caution.: Take a measure after more than 3 minutes have passed after removing the power cords in abnormal operation of
circuits since high voltage (DC310V) is maintained at the power terminal. Otherwise, it may cause electric shock.
Voltage of each part is as follows:
3-2-2. OSCILLATION CIRCUIT
Oscillation circuits are intended to generate clock for
synchronization for information transmission/receipt of logic
elements inside of the IC1 (MICOM) and generate basic time for
time calculation. Rated parts must be used since the OSC1 does
not operate or time calculated at the IC1 changes where SPEC
changes.
3-2-3. RESET CIRCUIT
The reset circuits are intended so that the whole of function is
started at the initial status by initializing various parts such as ram
inside of the MICOM (IC1) when power is applied to MICOM
again in input of initial power or by temporary power failure.
“LOW” voltage is applied to the reset terminal of MICOM for the
fixed time (10ms) at the start of power input.
During general operation, the reset terminal is at 5V (No MICOM
operates in case of poor reset IC).
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Part Both ends of VA1 Both ends of CE1 Both ends of CE2 Both ends of CE3 Both ends of CE4
Voltage 220 Vac 310 Vdc 16 Vdc 12.5 Vdc 5 Vdc