NEC DPro2070SB, Руководство по обслуживанию

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1.1.3 Sub power circuit
When the power switch is turned ON, the rectified and smoothed DC voltage (AC voltage x √ 2) is
supplied to pin 5 of IC903, and is charged to C930 through pin 1. When pin 1 reaches 5.7V, oscillation is
started in IC903, and the built-in output FET is put into operation to add the pulse voltage between pin 5
and pin 3 on the primary side of T902. The flyback voltage in proportion to the voltage on the primary
side is generated on the secondary side, then the DC voltage is generated with the half-wave rectifier
circuit composed of D971 and C971. The DC voltage generated at the secondary side is monitored by
IC922 through R976, R977 and R978. This information detected at IC922 is fed back to pin 1 of IC903
via PC902, and the ON period of output FET internal IC903 is controlled to keep the DC voltage on the
secondary side constantly. The flyback voltage in proportion to the voltage on the primary side is also
generated at pin 2 of T902. The pulse voltage generated at pin 2 of T902 is converted to the DC voltage
at D932 and C931, and supplied to pin 8 of IC901 and pin 4 of IC902 via Q902.
1.1.4 Main power circuit
When the P-SUS signal from microcomputer is turned to HI, Q902 is turned to ON, and the voltage approx.
+18V is supplied to pin 4 (Vcc terminal) of IC902 from pin 2 of T902.
When the voltage of pin 4 of IC902 reaches approx. +16V, oscillation is started in the circuit, and the
built-in output FET is put into operation to add the pulse voltage between pin 5 and pin 2 on the primary
side of T901. The flyback voltage generated at the secondary side in proportion to the one in the primary
side is rectified at D961, D963, D964, D965 and D967 and smoothed at C961, C963, C964, C965 and
C969 to generate the DC voltage. The DC voltage generated at the secondary side is monitored by
IC921 through R960, R961, R962 and R985. The information detected at IC921 is fed back to pin 1 of
IC902 via PC901, and the ON period of output FET internal IC902 is controlled to keep the DC voltage on
the secondary side constantly.
1.1.5 Demagnetizing circuit
When the power is turned ON or the manual demagnetizing function on OSM menu is set to ON, pin 47 of
IC102 on the main board is turned to HI, and Q950 and RL901 are also turned ON.
When RL901 is turned ON, the current flows to the demagnetizing coil, however, the demagnetizing
current gradually converges with the fever of TH902.
1.1.6 Power management circuit
This monitor carries the power management function. This function is effective only when being
connected with the personal computer carrying the power management function.
Mode H-SYNC V-SYNC State Display
NORMAL ON ON Displaying a picture Displaying a picture
SUSPENSION
OFF
ON
OFF
ON
OFF
OFF
No picture
CRT heater is
decreased voltage
mode (approx. 1.5V)
No raster
The power consumption and the indication of Power-On Indicator for each mode are as follows.
Mode Power consumption Power-On Indicator
NORMAL 135W Green
SUSPEND 3W or less Orange
The control signal executes the power management function is output from microcomputer IC102. The
control signal is composed of two signals, SUSPEND and P-OFF. The operating state of each signal is
as follows.
Control signal name Pin of IC102 Normal Suspension
SUSPEND Pin 5 H L
P-OFF Pin 42 H L