3.2 Base Band Chroma Delay Line IC STV 2180 :
The STV 2180 is an integrated base band chroma delay line with one line delay, which has been designed to
match chroma decoders with color difference signal outputs (R-Y) and (B-Y). This IC has dual switched
capacitors delay line with 3 MHz clock and integrated filters to suppress the residual clock components. It
designed to work in conjunction with STV 2112/2116/2118 and it allows an adjustment free application.
The inputs for this IC are as follows :
?(R-Y) at pin #2 coming from STV 2118
?(B-Y) at pin #14 coming from STV 2118
?Sandcastle Pulse at pin #6 coming from STV 2118
On the other hand, outputs of this IC are as follows :
?Delayed (R-Y) at pin #3
?Delayed (B-Y) at pin #4
4. HORIZONTAL OUTPUT AND EHT STAGE :
The horizontal pulses, from pin #36 of IC401, are connected to base of driver transistor Q601 through Q601,
R603, C601. The driver circuitry (Q601, R604, C602, L602, R608) drives the horizontal deflection output
transistor BU808DFI (Q602). TR601 is the EHT (Extra High Tension) transformer. The 112V supply voltage
for the stage is connected at #2. TR601 transformer generates EHT, focus and G2 voltages, required by
picture tube. Furthermore, the 200V supply for video output, 26V supply for vertical output and heater drive
current are derived from this transformer. The beam current information from pin #8 of TR601 is used for
reducing the contrast at excessive long term average beam current and compensation voltage to vertical
output to stabilize picture height. The flyback signal sample (AC coupled and clipped by R606, C614, C604,
D602, D601) is used to generate sandcastle pulse for video processor IC and horizontal pulse (Q603) re-
quired by uC.
5. VERTICAL OUTPUT STAGE (TDA 1771)
The TDA1771 (IC701) vertical deflection integrated circuit is used for output of vertical stage. Trigger pulses
from STV2118 feeds to pin #3 of TDA1771. The signal produced by built in ramp generator synchronizes
input trigger pulses. Amplitude is adjusted by an independent input pin (#4). Built in voltage generator output,
feedback information by pin #8, internal sawtooth signal and amplitude information are applied to output OP-
AMP. This output stage has also thermal protection and flyback generator for reliability and effectivity. Applied
pulse from STV2118, contains vertical position information as maximum dc level of signal and is extracted by
Q701 and fed as a part of feedback to output stage. Vertical shift DC supply is obtained via R716. The
amplitude control is supplied by STV2118. Vertical deflection output stage is supplied by +26V output of FBT
and D605, C603 circuitry.
6. SOUND OUTPUT STAGE (TDA2822M) :
TDA2822M is used as the AF output amplifier. It is supplied by +12V coming from a separate winding in the
SMPS transformer (T802). Pin #14 of the STV8223 ( or STV 8224) is AC coupled to the input pin #7 of the
TDA2822M via a resistor divider. Maximum audio output power at 10% THD is 1.5W. Q301 for start up
muting and Q302 for muting by uC are used, and an alarm signal by uC is fed to this input.
7. POWER SUPPLY (SMPS) :
The DC voltage sources required at various stages of the chassis are provided by an SMPS controlled by the
IC801 (MC44603 for common models and MC44604 for ?low power consumption on stand by mode? mod-
els). This IC is designed for driving, controlling and protecting the switching MOSFET transistor of SMPS
(Q801). This supply has three outputs; one 112V output which is used for horizontal output and 33V genera-
tion needed by tuner section, one 16V output for all small signal sections an uC and one for audio output
section. This chassis may be used in 90 - 270 volt with appropriate optional circuitry and components. The uC
which is supplied by a source designed regulator with zener diode (D814) controls stand by mode by switch-
ing Q803 (for 44604 application Q806).
6 |