Iiyama Vision Master Pro 451, Руководство по обслуживанию

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(2) MAIN POWER circuit
400V is supplied to this circuit from the POWER FACTOR circuit. Start-up resister R968 and R969 detect 4 pin of
IC951 voltage (VCC-IN) and activate internal start circuit of IC951. When 4 pin of IC951 voltage turns to 16V, internal
control circuit starts operation and auxiliary coil voltage between 8 and 9 pin of T950 (main transformer) is up to
approx.18V, and MAIN POWER circuit is activated.
IC950 detects the load of 28V output voltage from the T950 secondary and controls the feedback current in PC950
(photocoupler) by fed back to 1 pin of IC951 (OCP/FB).
The T950 secondary provides the following DC voltages:
Q
80V line: Supplied to the HIGH VOLTAGE OUTPUT (T501) and the VIDEO OUTPUT IC (IC202) and
the CUT-OFF IC (IC204) as power source.
R
28V line: Supplied to the HORIZONTAL DEFLECTION OUTPUT (variable B voltage control) circuit
and HORIZONTAL DRIVE circuit as power source.
S
15V line: Supplied to the each 12V POWER CONTROL circuit, the CRT CORRECTION circuit and the
VERTICAL OUTPUT IC (IC104, +) as power source.
T
–12V line: Supplied to the CRT CORRECTION circuit and the VERTICAL OUTPUT IC (IC104, –) as
power source.
Note : 1. The Switching frequency always vary because power supply is asynchronous.
2. The actual waveform is not static like as above waveform.
D950
IC951
AC-IN
90-132/
198-264V
K901
1
4
2
T950
PC950
POWER FACTOR
circuit
3 15V
-12V
80V
28V
IC951 pin 3 Drain output
(200V/div)
IC951 pin 1 OCP/FB input
(2V/div)
<Waveform> fH=91.2kHz fV=85Hz 1280 × 1024