Samsung CX528ZSE Service Manual page 21

1. INTRODUCTION
The P-54S series chassis assembly is a solid state single board chassis and consists of 5 IC's. It has a chassis design
which makes use of the VIF/SIF processing IC(LA7520/KA2919), large-scale integration for the video/chrome/deflection
processing circuits (TA769BAP /KA2154), the vertical output IC(AN5512/KA2131), TV/VIDEO switching IC(TEA2014), and PAL
/SECAM switching & SECAM chroma IC(M5139AP).
The varactor tuner used with this chassis is mounted on the chassis circuit board. Servicing this chassis is greatly enh—
anced by the fact that main parts of circuits are integrated. The main circuit board of this P-54S series chassis is de—
vieded into the following functional areas, and the components in each eree on it are essigned ae particular number series,
as indicated bellow :
100 series ------~---- Tuner /IF/AFT/AGC processing, 12V regulator.
200 series ---------—— Video /Luminance/Sync processing.
300 series ------—--- Vertical deflection.
400 series -------~--- Horizontal deflection.
500 series --------~- Chroma processing, CRT drive circuits.
600 series --~------- Sound processing.
800 series -------——— AC input, power supply circuits.
XN series ----~----- SECAM chroma circuits.('X' means one of R,C,Q,J markings)
XS_ series -~------~-- PAL/SECAM switching circuits.
2.17 SECTION
(1) Preamplifier /SAW filter.
The IF input from the tuner is preamplified in a tuned amplifier (Q161) and applied to the SAW (surface
Acoustic Wave) filter device (Z101) which establishes the proper IF respanse, with only one adjustment of
T101 required for maximum gain.
The input circuit for the SAW filter consists of several functional elements. R100 and L161 are used pri-
marily to match the IF input to a 75 ohm cable (75 ohm input impedance). Q161—preamp transistor is
biased as a chass "A" amplifier to provide 20dB. This 20dB gain compensates for the 20dB loss in the
SAW filter.
L162 is a SAW input coil. T101 (SAW output coil) is an adjustable coil which resonates with the capa—
citance of the SAW filter and the IC101 to provide maximum gain at the IF center frequency. At the
same time the impedance is adjusted to a level which will give the proper mismatch to provide the
desired amount of reduction of TTE (Triple Transit Echo).
A brief description of TTE is as follows : As an acoustic wave travels within the SAW filter, it induces
a voltage across the electrodes and the external load. This voltage in turn generates another acoustic
wave. This wave travels back to the input where a quarter of its energy is similarly reflected and travels
to the output. The echo is 12dB lower than the original wave. Since the echo has made three trips
across the substrate, it is referred to as TTE.
A SAW device consists of metal electrodes (or fingers) deposited on a highly polished crystalline piezo—
electric substrate. These electrodes—usually composed of a thin aluminum film—form an_ interleaved
pattern on a substrate surface and together make up the device's transducer; the most elementary
transducer employs electrode centers spaced 1/2 or 1/4 operating frequency wavelengths apart.
When an RF signal is applied to the input trensducer electrode pair, an electric field is generated and
the piezo-electric substrate material undergoes mechanical stress, caussing vibretions—an acoustic wave—to
propagate along the surface. This SAW remains on the surface and only slightly penetrates the crystai-
line substrate.
Because the SAW transducer is bidirectional, only half its transmitted power radiates toward the output :
the other half radiates toward the substrate's edge and is lost or absorbed in a damping material. The
waves that propagate to the output transducer produce en electric field between this electrode's fingers
which in turn generates a voltage across the output.
The SAW filter, as utilized in the p-54S series chassis, provized all the band shaping for the IF and gen—
erates the IF response curve formerly obtained with the LC circuits with adjustable coil (1101).
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