VESTEL 17MB18, Service Manual

Page: 9 / 76

3. SYSTEM BUILDING BLOCKS
17MB18 chassis main blocks are as follows:

Analog Front End
: UOCIII (Microcont Video Proc Sound Proc IF), CTI, Tuner, SAW
filters, Audio Amp., DAC

Back End
: PW1306(Microcontroller, Scaler, OSD, Keyboard/IR Interface)

Side Board(s)
: Keyboards, IR/LED Boards, TTL Panel Interface Cards, VCbCr Input Board (Optional)
3.1. Analog Front End
17MB18 Main Board consists of two major blocks. The first block is analog front-end and this block is handled by
UOCIII chip that is highly multifunctional. This IC does demodulation of Video & Audio from Tuner IF, CVBS, Audio,
RGB, SVHS input selection and processing. It has an audio processor that supports equalizer or tone control, volume
control, AVL, surround effect etc and supplies amplifier, headphone and CVBS & audio line outputs. It handles video
processing such as colour standard detection and demodulation, picture alignment (brightness, contrast, colour etc.). The
IC also does teletext decoding with 10 pages text memory. After video processing, the processed video is applied to
PW1306 chip in RGB format.
The TV Tuner is an asymmetrical IF output type and is PLL controlled. For multistandard reception, a switchable SAW
filter is used as the sound filter and it is controlled by SAW_SW output from UOC. After the SAW filter block, IF signal
is applied to UOC IF inputs (VIFIN[1,2] and SIF[1,2]).
As UOCIII can handle all the audio processing, there is no need for additional audio processor solution on the board.
UOC supports three Audio outputs. These outputs are assigned to Headphone, Speaker and Scart Audio line outputs. The
board employs TDA7056A and TDA1308 to drive speaker and headphone outputs respectively. As another dedicated
output for Audio Line out from jack is not possible in UOC, this line out signal is obtained by using I2S input DAC
CS4335. UOCIII I2S output is converted to anolog signal by DAC CS4335.
3.1.1.
Tuner
As the thickness of the TV set has a limit, a horizontal mounted tuner with longer connector is used in the
product. The tuning is available through the digitally controlled I
2
C bus (PLL). Below you will find info on the
Asymmetrical Tuner in use.
General description:
The tuner meets a wide range of applications. It is a combined VHF, UHF tuner suitable for CCIR systems
B/G, H, L, L’, I and I’. The low IF output impedance drives a wide variety of SAW filters with sufficient
suppression of triple transient.
Features:
 Small sized UHF/VHF tuners
 Systems CCIR: B/G, H, L, L’, I and I’; OIRT: D/K
 Digitally controlled (PLL) tuning via I
2
C-bus
 Off-air channels, S-cable channels and Hyper band

Z
S(AE)
Aerial source impedance (unbalanced) 75 Ohm
PIN SYMBOL DESCRIPTION
1
AGC
Automatic Gain Control Voltage 4

0.1
2
TU Tuning voltage monitor (output)
3
AS
I
2
C-Bus Address Select
4
SCL
I
2
C-Bus Serial Clock
5
SDA
I
2
C-Bus Serial Data
6
n.c. Not Connected
7
V
s
Supply V5V

0.125
8
ADC
ADC Input
9
V
ST
Fixed tuning Supply V33V

0.5