Circuit Explanations - Mitsubishi Electric LT-3280 Service Manual

Circuit explanation
1 . 1 . 1 . 1 . 1 . V V V V Video circuits ideo circuits ideo circuits ideo circuits
ideo circuits
It explains the video circuits of LT-3780,LT-3280(Model name of display side only : LT-3780D,LT-3280D).
It corresponds to various inputs (PC, Monitor Link
It explains the composition and its function of an video circuit.
(Refer to an attached "Video block diagram of LT-3780D,LT-3280D", regarding as the flow of video signal.)
1-1. Video input circuit of PC
In PC input, it is inputted into IC400 of the signal processing IC via Following IC
(A) IC203 : Analog-to-digital conversion IC (AD9888KSZ-170 : Analog devices)
The video signal (R, G, B) of PC input is changed into a digital signal (8 bits each) from an analog
signal. Moreover, by this IC, it has the function below besides digital conversion.
Contrast adjustment for PC
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brightness adjustment for PC
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This IC is controlled by register control of IC203 via 3.3V IIC-bus
(B) IC201 : Invert IC with the Schmidt trigger (74LCX14 : Fairchild)
It is IC which inputs the horizontal sync signal and vertical sync signal of PC input.
Since there are what has a bad rising and falling characteristic and what has low amplitude in the
sync signal outputted from PC, it is necessary to modify the waveform.
It corresponds to the above-mentioned waveform as follows by this IC.
a bad rising and falling characteristic. : Rise-time and fall-time is carried out early.
-
a waveform is noisy
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Low Amplitude
-
Since 74LCX14 is a invert circuit, if its gate pass twice and it has united polarity.
(C) IC200 : 1K-bit EEPROM (24LC21ATI : Microchip)
This is the IC for EDID of PC.
This IC has important information about PC input such as product code, serial number, video
specification, proposed timing, color information etc.
(D)IC202 : AND-circuit IC (SN74LVC08APWR : Texas Instruments)
This IC is to disable the H, V sync signal line connected to IC which power supply is dropped while
stand-by. It can operate correctly by using this.
This is controlled by ENABLE singnal from MPU(IC700) ( L : disable)
(E)IC204 : D Flop-Flop IC(TC74VCX74FT : TOSHIBA)
The role of this IC is to synchronize H sync signal and V sync signal.
For output signal of IC203, H sync is synchronized by dot-clock from IC203, but V sync is not
Synchronized by H sync. This IC uses to be operated without miss-operation.
(F)IC2A0 : Color conversion IC(M66471FP : Mitsubishi)
This IC uses to perform Color conversion function such as PerfectColor, Colorview.
(G)IC2A1 : TMDS-Transmitter IC(SII160CTG100 : SiliconImage)
This IC uses to convert signal's specification from TTL to TMDS (differential signal).
Since the input port of latter IC (IC400: Signal processor ) could use only the TMDS input, this input
specification was united by this IC.
MODELS: LT-3280D/LT-3780D
A/V Input).
TM
: It prevents that the mistaken pulse occurs by the Schmidt circuit.
: If voltage threshold is satisfied, high level will output in 3.3V.
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3.3V IIC-bus 3.3V IIC-bus
3.3V IIC-bus to MPU(IC700) 3.3V IIC-bus