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ST 03
9. Output Power Stages
This section describes the power output stages for video, audio, line
and field scanning system.
9.1 Field Output (IC200)
The TDA8170 IC200 is a power output amplifier designed to drive the
vertical scan coils on the CRT yoke. The saw-tooth waveform is fed into
pin 1 from pin 7 of IC800. Internal to IC200 is the flyback generator. The
flyback generator produces a pulse equivalent to the field blanking
period during which time no visible video appears on the screen.
The saw-tooth voltage waveform is converted to a current waveform
that drives the field scan coils.
The flyback part of the waveform is also used to generate the vertical
sync pulse for the OSD. The circuit R207, D202 and R208 slice the
waveform to give the vertical sync pulse and to limit it to a voltage of
no greater than 4.7V.
9.2 Line Output Stage
The line output stage has to provide a number of things for the system.
Firstly, it provides the power and the waveform to drive the horizontal
scan coils on the CRT yoke. Secondly, it provides the voltages for the
tube, EHT final anode drive, focus voltage and G2. Thirdly, it provides
two secondary low tension voltages, 15V and 26V, and after passing
through a fixed voltage regulator, IC300, 12V. Fourthly, it provides on
the primary side of the transformer the 150/180V supply for the tube
base video output amplifiers and, finally the voltage for the heaters on
the CRT of around 6.3V.
The tuning capacitor C300 is selected by the type of tube fitted as are
the correction circuits L300, L301, R300 and R301.
9.3 Line Driver
The line drive signal from IC800 is first clamped by D804 then inverted
by TR800. The resulting waveform is fed to TR301 line driver stage.
The drive is applied to the line output transistor TR302 across the line
driver transformer T311. TR302 drives both the diode split transformer
T300 and the line scan coils connected to PL351. The field coils are
also connected to PL351.
9.4 12V Regulator Circuit
The 15V generated off the low side secondary of the diode split LOPT
is used in the beam current sensing circuit prior to it being fed into the
12V fixed regulator IC300. From the primary side of the diode split there
is a circuit which is used to produce a low level line flyback pulse. This
is the circuit around TR300. The flyback pulse is used by the IC800 for
synchronization in PLL's and also for the line blanking during video for
line flyback period. Also from this circuit is supplied the horizontal sync
pulse for the OSD of the microcontroller.
9.5 Flyback Pulse Circuit
The flyback pulse is fed into TR300 via two high value resistors R302
and R303. The high values are because at the take-off point the flyback
pulse could be in excess of 1kV. The capacitor C306 is a speed-up
capacitor to improve turn on and off characteristics of TR300. The
diode D305 clamps the incoming flyback pulse to 5V so that the output
at the emitter of TR300 does not rise above 5V and that the base of the
transistor is not spiked by excessive transient voltages.
10. Video Output Stages
The video output transistors TR900, 901, 902 are driven directly from
the buffer transistor circuits at the output RGB of IC800. The gain of the
stage which determines the video voltage swing applied to the tube
cathode is set by a register in IC800. The actual gain control known as
contrast is also a register in IC800 as is the brightness control.
The capacitors connected across the emitter resistor is to give a little
extra gain at the HF end. The transistors TR903, 904, 905 are the
dark/light current sense transistors and feed the dark current sense on
IC800-(20) for auto grey scale.
10.1 Auto Grey Scale
When the video output transistor is driven with peak white which equals
max. beam current then the voltage drop across the diodes increases
thereby making a difference of potential between base and emitter
causing the transistor to conduct. This produces an output by the
collector proportional to the high beam current. As the output transistor
GRUNDIG Service
Circuit Description
is turned off at black level, so the reverse happens with the sense
transistors until we are left with a voltage that represents the dark tube
leakage current which is a dark reference current for the tube.
10.2 Tube Base Interconnect
Connection to the tube base is via two connectors CN901 and CN902
for the main connectors, then by single connectors for the focus and
G2. The final anode voltage is applied directly to the connection on the
side of the tube bulb. The tag coating connection is made by a single
tag to the tube base panel ground.
11. Teletext Options
The text chip-set being used is the Texas Instruments 2 chip Videotext
decoder set. Depending on what system is required Eurotext or Unitext
determines what IC650 will be. A table of components that change are
shown in the "Text Table" on the schematic. IC651 is the data slicer and
timing signal generator. The timing signals are all generated with
respect to the master clock which is derived from the crystal XT650.
The value of this crystal is twice the data rate of the text signal
13.875MHz.
This clock is synchronized to the clock run-in signal at the front of the
data packet. The data is then output to IC650 along with data clock and
the other timing signals. IC650 then decodes the data and produces
the text display for the screen. If the TV signal is present then the whole
thing is locked to the incoming sync signal.
If the TV signal is not present then the system generates its own sync
so that text stored in memory can still be displayed in a locked form. All
commands and customer selection are engaged via the I
2
C bus which
is attached to the microcontroller I
2
C bus.
The RGB outputs are then fed to the input for external RGB on IC800.
The control signal for the blanking function is taken to switch input of
IC800-(21). For Eurotext the outputs are directly fed to IC800 whilst
buffers are used for Unitext.
12. Power Supply to MSP 3400/3410
Power is supplied to the MSP from pin 4 of plug PL102. This is an 8V
supply derived from the chopper transformer and is therefore available
when the receiver is in standby. The 8V supply is regulated to 5V by IC3
and applied to the MSP via RFI filters (L2, CT2 and L4, CT4) to pins 18
and 57 of the MSP. The 8V is supplied to pin 39 via the RFI filter L3,
CT3. The reason the 8V line operates in standby is because this locks
the internal audio switches into pre-set positions when the 5V voltage
is removed so as to reduce the standby power. TR4 is open circuit
during standby.
12.1 MSP Operation
The ITT MSP3410 decodes FM, dual-channel and NICAM sound; the
MSP3400 does not do NICAM. The intercarrier input is applied to
pin 58 for all systems except France where an additional filter may be
required. The input is then to pin 60. The MSP is controlled by the clock
and data lines (I
2
C) from the microcontroller. The IC generates an
internal clock from the crystal on pins 62, 63 at 18.432MHz. Reset
components are on pin 24. Note there are no adjustments on the MSP
as all processing is done digitally. Note, the volume control is now an
I
2
C operation as is treble, bass and balance.
13. Second Peritel and Mute Circuit
Video from the second peritel is supplied from pin 20 of Peritel 2. This
is then buffered by TR20 and applied to IC4-(1). IC4-(2) carries video
derived from the tuner and IF amp. The switch position is controlled by
IC4-(10). The microcontroller (pin 5 DA4) controls the switch position.
The output of IC4 (pin 15) is applied to the times-2 gain stage TR1, TR2
and out to Peritel 1, input of IC400 -(10) and so to the picture tube if
there is no input from Peritel 1. Mute Circuits TR5 and TR7 mute the
loudspeaker channels. TR12, 13, 10 and 11 mute the two Peritel audio
outputs. The mute circuit is driven by port zero and port 1 (pins 4 and 5)
of IC1. Pin 5 mutes the speaker channel and pin 4 the Peritel channels.
TR9 detects when the receiver is switched off and mutes all audio
outputs.
14. Audio Amplifier
The audio amp generates 6+6 watts of RMS power into 8R speakers.
The power is derived from a 21 volt winding on the chopper trans-
former.
ST 03
Alignment
All adjustment controls not mentioned in this description are adjusted during production and must not be re-adjusted in the case of repairs.
Measuring Instruments: Oscilloscope with 10:1 test probe, colour test pattern, high resistance voltmeter.
Service Mode:
In this mode the alignment of Geometry, Peak White Level and AGC can be carried out. To call up this mode, either the remote control or TV front
controls can be used.
Call up Service Mode:
To enter the service mode, depress and hold the channel change buttons "P+" and "P-" on the front as the TV is switched on and hold until a picture
appears. The service menu will be at the bottom of the screen G L V H R G B A. To choose a function select menu on the remote control or
simultaneously depress "V+" and "V-" on the front of the TV, but only briefly. Adjustment of the selected function is by depressing "P+" or "P-". Choosing
another function will automatically store the adjustment of the previous function. To return to normal TV mode select TV on the remote control or "V+"
or "V-" on the TV.
Checks and adjustments after replacement or repair of:
Power Supply: 1., 3.
Horizontal Deflection: 2., 3., 6.
CRT, CRT-Panel: 2., 4.
Tuner: 5.
IC1400: 5., 7.
IC600: 8.
Alignment
Preparations
1. +B Voltage
Set luminance to mimimum.
Voltmeter to the cathode of D115.
2. Screen grid
Feed in a crosshatch or TV picture.
voltage U
Brightness ( ) Minimum.
G2
Contrast ( ) Maximum.
Select Service Mode "G".
3. Geometry:
Feed in a convergence test pattern:
Vertical Linearity
Select "L" in the Service-Mode.
Vertical Height
Select "V" in the Service-Mode.
Horizontal Shift
Select "H" in the Service-Mode.
4. White balance
Feed in a FuBK test pattern.
Set the colour contrast ( ) to minimum.
Set the contrast ( ) to maximum.
Adjust the screen brightness ( ) so that the gradation from
the darkest grey scale value to black is just still visible.
Select "R", "G", or "B" in the Service Mode.
5. Tuner-AGC
Feed in a standard test pattern at a channel in the upper
range of the UHF; the RF should be ≥3mV (70dBµV, free
of noise).
Select "A" in the Service Mode.
6. Line sharpness
Feed in a convergence test pattern:
Contrast ( ) to maximum.
Set the brightness so that the black background of the test
pattern is just brightening.
7. Vision
Feed in a convergence test pattern of 38.9MHz (39.5MHz
demodulator
on PAL I) to tuner contact 13 via 1nF.
8. SAT 6MHz
Feed in a convergence test pattern (UHF) on the TV set.
Connect the oscilloskop to IC600-(12).
2 - 3
1-1
GRUNDIG Service
Alignment
Alignment Process
With control VR100 set the voltage +B as specified in the
table CRT (page 4-22).
Adjust control G2 (at the bottom of the split transformator)
so that no red or green square appears on the screen.
If the G2 is too high –> a red square appears on screen.
If the G2 is too low –> a green square appears.
Adjust with "P+" or "P-".
Adjust with "P+" or "P-".
Adjust with "P+" or "P-".
Set "P+" or "P-" so that no colouration of grey bars is
visible.
With "P+" or "P-" adjust the voltage on tuner contact 1 to
5.4...5.6V.
With the focus control "FOCUS" (upper adjustment control
of the split transformator) adjust the horizontal lines for
maximum sharpness.
With filter L401 set the DC level at IC400-(2) to 5.25V.
Adjust L604 to minimum video.
3 - 1
1-2
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