Daewoo 14A5 Service Manual page 18

No Name
13 INT CVBS INPUT
17 EXT CVBS INPUT
14 GROUND
15 AUDIO OUTPUT
16 DECOUPLING
FILTER TUNING
18 BLACK CURRENT
INPUT
19 BLUE OUTPUT
20 GREEN OUTPUT
21 RED OUTPUT
22 V-GUARD INPUT/
BEAM CURRENT
LIMITER
23 RED INPUT
24 GREEN INPUT
25 BLUE INPUT
26 RGB INSERTION
SWITCH INPUT
27 LUMINANCE INPUT
Description
A voltage detection circuit is connected to both pins.
- pin12 if V12 <6.8V than a power on reset, POR, is generated. The Hout
output is disabled immediate.
- pin37 if V37 <5.8V than the horizontal output is disabled immediate.
It is recommended that the CVBS1 int and CVBS2 ext input amplitudes are
1 Vpp (inclusive sync amplitude).
This, because the noise detector switches the
(i.e. auto 1mode when FOA, FOB = 0,0) when noise level exceeds
100mVrms (i.e. at S/N of 20dB).
All internal circuits are connected to this ground pin 14.
The output signal is volume controlled and is active for both internal and
external audio signals. The nominal gain is +9dB and -71dB, which gives
a total control range of 80dB.
The output signal range therefor is 0.14- 1400mVrms
The bandwidth is >100kHz, the DC level is 3.3V and the output impedance
is 250 .
Voltage variations at pin 16, which can be due to external leakage current or
crosstalk from interference sources, should be less than 50mV to ensure that
tuning of filters/delay cells remains correct.
For correct operation of the loop CURRENT information is supplied to the
black current input pin.
The RGB outputs are supplied to the video output stages from pins 21, 20
and 19 respectively.
For nominal signals (i.e. CVBS/S-VHS, -(R-Y)/- (R-Y), TXT inputs) and for
nominal control settings, then the RGB output Signal amplitudes is
typically 2VBLACK_WHITE.
Vertical Guard
With this function, the correct working of the vertical deflection can be
monitored. If the vertical deflection fails, the RGB outputs are blanked to
prevent damage to the picture tube.
Beam current limitinq
The beam current limiting function is realised by reducing the contrast (and
finally the brightness) when the beam current reaches s too high level. The
circuit falls apart in two functions:
- Average beam current limiting (ABL): reacting on the average content of
the picture
- Peak white limiting (PWL): reacting on high local peaks in the RGB signal.
The Rin, Gin, Bin input signals (nominal signal amplitude of 700mV) are
AC coupled to pin 23, 24 and 25 respectively.
Clamping action occurs during burstkey period.
The table below a survey is given of the three modes which can be selected
with a voltage on RGB insertion switch input pin ;
Vpin26 I2C function
0.9V-3V IE1=0
IE1=1
> 4V IE1=X
An nominal input signal amplitude of 1 Vblack-white MUST be DC coupled
18
1 loop to slow mode
Selected RGB signal
RGB(internal)
Rin,Gin,Bin
(fast insertion on pin23,24,25)
OSD can be inserted at the RGBout pins