Samsung CX528ZSE Service Manual page 33

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Consequently, the video signal is blanked because Q201 is turned off.
And then the —Y signal of Pin 23 is finally applied to the emitter of R.G.B output TR's (Q501-Q503)
through Q201.
CRT drive stage.
The CRT drive stages are conventional—they are emitter driven for the wideband luminance signal (gro—
und base) and base driven for the narrow band chrominance signal (grounded emitter). The lumin—
ance (~Y) signal is brought into the emitters of the three output stages through the R and C, and
the chroma difference signals are applied to the bases of the three output stages.
The gain of each stage can be controlled by the adjustable emitter resistors (VR502—VR506) although
the set-up procedure ensures that at least one stage will be operating at its maximum gain setting.
For complete independence of the set-up controls, the three emitters must be at the same DC poten-
tial. Since the base-emitter voltage drops will be the same or within very close limits, it follows that
the DC outputs from the chrominance demodulator (IC501) must also be held to close limits. The fixed
emitter resistors (R513, R517, R518) are by-passed by a small capacitors (C514, C515, C516) to provide
some frequency compensation for Q201 emitter RC time constant.
The use of a higher load resistor is now possible requiring less power than earlier designs for the same
gain and bandwidth, so no additional heat sink for each output TR's is required at the collector tabs.
This P-54S_ series chassis has the service swithch (SW201).
The purpose is to help in making adjustments for the picture tube.
There are usually three settings.
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. Normal position : This is the operating position of the switch, with a normal picture on the raster.
2. Purity check position : In this position, Y signal is applied to the red out TR (Q503). So it's very
easy to confirm the purity adjustments conveniently.
3. Service position (for white balance adjustment) : In this position, the vertical deflection is disabled to
collapse the raster into one horizontal line across the screen. The purpose is to concentrate the
illumination to help determine visual cutoff when adjusting the screen grid voltages of the CRT. Screen
volume mounted on the FBT varies the screen grid voltage for each of the electron guns. The pur—
pose is to make them all have the same cutoff characteristics at a very low light level.
And then adjust the white balance, rotating the low light volumes (VR502—504) slightly to the right.
After finishing screen adjustments, put the service switch to the normal position, and then adjust the
R,B drive volumes (VR505, VR506).
Drive control adjustments vary the amount of Y signal for each of electron guns, and it's for different
phosphor efficiencies of the CRT. The drive volumes are adjusted to produce white highlights in @ mo—
nochrome picture.
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