4
3.1.5 Other Functions :
Volume Control and Mute output is pin # 10. The voltage range for volume control is 0.5V to 5V, whereas below
0.1V is used for muting. The output of this pin is controlled by microcontroller via bus and the value is saved in related
register of the STV 2118.
The selection of the IF standard (Positive or Negative Vision Modulation) and the TV / SCART(AV) mode is
controlled by bus. The selection is converting in four voltages which are used to control the IF ICs STV 8224 and
STV 8225 on pin # 11. Related voltage levels and their situations are tabulated as follows:
Table 3.1 Related voltage levels and their situations for pin # 11 of STV 2118.
SITUATION
VOLTAGE RANGE (V
11
)
STANDARD
SOURCE
MIN.
MAX.
NEGATIVE
TV
0
0.7
POSITIVE
TV
2.9
3.8
POSITIVE
SCART
5.2
6.1
NEGATIVE
SCART
7.88
9
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) required 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.
