Rgb Out Board - Ikegami HTM-1550R Service Manual

2-4 RGB OUT BOARD
(1) Outline
Th.is board is composed of the circuit, which amplifies RGB video
signals from the VIDEO PROC. BOARD to the CRT drive level and
the circuit which samples the beaJn, reed back pulse.
(2) Circuit description
(a)VIDEOAMP
Amplifier ciicuit (gain=21 times) composed of ca.scade-rouuected R,
G and B channels.
The Reh block is composed ofTRlOl, TR103 and TR104, the Gch
block is composed ofTR201, TR203 and TR204, and the Bch block
is composed ofTR301, 1R303 and 1R304.
(b) EMITTER FOLLOWER & CURRENT SWITCH
Composed of the emitter follower circuit
which
SUppres.5CS
changes
in CRT
drive characteristics
and sets low impedance, switch circuit
which limits current from the difference in the HDTV and SDTV
video band, and switch circuit which samples the beam feedback:
pulse.
lu the normal video range, as 1R105, TR205, 1R305, 1R108,
1R208 and 1R308 are ON (in the HDTV mode, TR109, 1R209,
and 1R309
an:
also on\ TR106, TR206 and 1R306 operate as the
emitter follower circuit.
Only during the beam reedback pulse range (the 3 homs after
V.BLK ends) do all
1Rs go off. The current from the cathode is
passed through Rl25, R225 and R325, and the current converted to
voltage is reed back to the VIDEO PROCESS circuit IClOl,
IC201, 1001 and 1R408 fum the buffer circuit.
lu the HDTV mode, 1R109, 1R209 and 1R309 are turned ON to
increase the rurrent to the emitter follower circuit and broaden the
video range. (OIi in the SDTV mode.)
1R407 is
a limiter
circuit
to prevent the
sampled pulse from rising
ex~ive)y.
(3) Adjustment procedure
' Unless specified, the HDTV color bar (100% )ISDTV color bar
(75%) is used as the input signal.
(a) VRl0l: R FREQ COMP
VR201:
G FREQ COMP
VR301:BFREQCOMP
CD
Correct
the low frequency response (inclinations such as waveform
signal) of the video signal.
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