Sharp 21LF-90H (serv.man3) Service Manual ▷ View online
5
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CHASSIS
SAFETY PRECAUTIONS
The service of this TV set must be carried out by qualified persons only. Components marked with the warning symbol
on the circuit diagram or on the Parts Listing, are critical for safety and must only be replaced with an identical component.
on the circuit diagram or on the Parts Listing, are critical for safety and must only be replaced with an identical component.
- Power resistor and fused resistors must be mounted in an identical manner to the original component.
- When servicing this TV, check that the EHT does not exceed 26kV.
- When servicing this TV, check that the EHT does not exceed 26kV.
TV set switched off:
Make short-circuit between HV-CRT clip and CRT ground layer.
Short C809 before changing IC800 and IC801 or other components in primary side of the SMPS part.
Short C809 before changing IC800 and IC801 or other components in primary side of the SMPS part.
Do not try to test Q801 gate source junction if C809 is charged, your meter will turn on the transistor which will discharge
the capacitor resulting in a drain source short circuit. Do not discharge C809 quickly with a screwdriver etc. The very
high current produced can damage the internal connections of the capacitor causing failure at a later date. Remember
when checking voltages to use a return path on the same side of TR802 for the Voltmeter earth to obtain the correct
readings.
the capacitor resulting in a drain source short circuit. Do not discharge C809 quickly with a screwdriver etc. The very
high current produced can damage the internal connections of the capacitor causing failure at a later date. Remember
when checking voltages to use a return path on the same side of TR802 for the Voltmeter earth to obtain the correct
readings.
Measurements:
Voltage readings and oscilloscope traces are measured under the following conditions:
Antenna signal’s level is 60dB at the color bar pattern from the TV pattern generator. (100% white, 75% color saturation)
Brightness, contrast, and color are adjusted for normal picture performance.
Mains supply, 220VAC, 50Hz.
Voltage readings and oscilloscope traces are measured under the following conditions:
Antenna signal’s level is 60dB at the color bar pattern from the TV pattern generator. (100% white, 75% color saturation)
Brightness, contrast, and color are adjusted for normal picture performance.
Mains supply, 220VAC, 50Hz.
DO NOT CHANGE ANY MODULE UNLESS THE SET IS SWITCHED OFF
The mains supply part of the switch mode power supply’s transformer is live.
Use an isolating transformer.
The receiver complies with the safety requirements.
The mains supply part of the switch mode power supply’s transformer is live.
Use an isolating transformer.
The receiver complies with the safety requirements.
PERI-TV SOCKET
21
21 19 17 15 13 11
9
7
5
3
1
20 18 16 14 12 10
8
6
4
2
SCART PINING
1 Audio right output 0.5 Vrms / 1K
1 Audio right output 0.5 Vrms / 1K
2 Audio right input 0.5 Vrms / 10K
3 Audio left output 0.5 Vrms / 1K
4 Ground AF
5 Ground Blue
6 Audio left input 0.5 Vrms / 10K
7 Blue input 0.7 Vpp / 75 ohm
8 AV switching input 0-12 VDC / 10 K
9 Ground Green
10 -
11 Green input 0.7 Vpp / 75 ohm
12 -
13 Ground Red
14 Ground Blanking
15 Red input 0.7 Vpp / 75 ohm
16 Blanking input 0-0.4 VDC, 1-3 VDC / 75 Ohm
17 Ground CVBS output
18 Ground CVBS input
19 CVBS output 1 Vpp / 75 ohm
20 CVBS input 1 Vpp / 75 ohm
21 Ground
17 Ground CVBS output
18 Ground CVBS input
19 CVBS output 1 Vpp / 75 ohm
20 CVBS input 1 Vpp / 75 ohm
21 Ground
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CHASSIS
1. INTRODUCTION
11AK44 is a 90° chassis capable of driving 20"/21" tubes at the appropriate currents. The chassis is capable of operating
in PAL, SECAM and NTSC standards. The sound system is capable of giving 4 watts RMS output into a load of 16
ohms. 7 page SIMPLETEXT is provided. The chassis is equipped with a single-deck 21 pin Scart connector.
in PAL, SECAM and NTSC standards. The sound system is capable of giving 4 watts RMS output into a load of 16
ohms. 7 page SIMPLETEXT is provided. The chassis is equipped with a single-deck 21 pin Scart connector.
CIRCUIT DESCRIPTIONS
2. SMALL SIGNAL PART WITH STV2248
2. SMALL SIGNAL PART WITH STV2248
STV2248 video processor is essential for realizing all small signal functions for a color TV receiver.
2.1 Vision IF amplifier
The vision IF amplifier can demodulate signals with positive and negative modulation. The PLL demodulator is completely
alignment-free. Although the VCO (Toko-coil) of the PLL circuit is external, yet the frequency is fixed to the required
value by the original manufacturer thus the Toko-coil does not need to be adjusted manually. The setting of the various
frequencies (38.9 or 33,8 MHz) can be made via changing the coil itself.
alignment-free. Although the VCO (Toko-coil) of the PLL circuit is external, yet the frequency is fixed to the required
value by the original manufacturer thus the Toko-coil does not need to be adjusted manually. The setting of the various
frequencies (38.9 or 33,8 MHz) can be made via changing the coil itself.
2.2 QSS Sound circuit (QSS versions)
The sound IF amplifier is similar to the vision IF amplifier and has an external AGC de-coupling capacitor. The single
reference QSS mixer is realised by a multiplier. In this multiplier the SIF signal is converted to the inter-carrier frequency
by mixing it with the regenerated picture carrier from the VCO. The mixer output signal is supplied to the output via a
high-pass filter for attenuation of the residual video signals. With this system a high performance hi-fi stereo sound
processing can be achieved. The AM sound demodulator is realised by a multiplier. The modulated
sound IF signal is multiplied in phase with the limited SIF signal. The demodulator output signal is supplied to the output
via a low-pass filter for attenuation of the carrier harmonics. The AM signal is supplied to the output via the volume
control.
reference QSS mixer is realised by a multiplier. In this multiplier the SIF signal is converted to the inter-carrier frequency
by mixing it with the regenerated picture carrier from the VCO. The mixer output signal is supplied to the output via a
high-pass filter for attenuation of the residual video signals. With this system a high performance hi-fi stereo sound
processing can be achieved. The AM sound demodulator is realised by a multiplier. The modulated
sound IF signal is multiplied in phase with the limited SIF signal. The demodulator output signal is supplied to the output
via a low-pass filter for attenuation of the carrier harmonics. The AM signal is supplied to the output via the volume
control.
2.3 AM Demodulator
The AM demodulated signal results from multiplying the input signal by itself, it is available on AM/FM output.
2.4 FM demodulator and audio amplifier (mono versions)
The FM demodulator is realized as narrow-band PLL with external loop filter, which provides the necessary selectivity
without using an external band-pass filter. To obtain a good selectivity a linear phase detector and constant input signal
amplitude are required. For this reason the inter-carrier signal is internally supplied to the demodulator via a gain
controlled amplifier and AGC circuit. The nominal frequency of the demodulator is tuned to the required frequency (4.5/
5.5/6.0/6.5 MHz) by means of a calibration circuit that uses the clock frequency of the µ-controller/Teletext decoder as
a reference. The setting to the wanted frequency is realized by means of the software. It can be read whether the PLL
frequency is inside or outside the window and whether the PLL is in lock or not.
With this information it is possible to make an automatic search system for the incoming sound frequency. This is
realized by means of a software loop that alternate the demodulator to various frequencies, then select the frequency
on which a lock condition has been found. De-emphasis output signal amplitude is independent of the TV standard and
has the same value for a frequency
deviation of ±25 kHz at the 4.5 MHz standard and for a deviation of ±50 kHz for the other standards. When the IF circuit
is switched to positive modulation the internal signal on deemphasis pin is automatically muted. The audio control
circuit contains an audio switch and volume control. In the mono inter-carrier sound versions the Automatic Volume
Leveling (AVL) function can be activated. The pin to which the external capacitor has to be connected depends on the
IC version. For the 90° types the capacitor is connected to the EW output pin (pin 20). When the AVL is active it
automatically stabilizes the audio output signal to a certain level.
without using an external band-pass filter. To obtain a good selectivity a linear phase detector and constant input signal
amplitude are required. For this reason the inter-carrier signal is internally supplied to the demodulator via a gain
controlled amplifier and AGC circuit. The nominal frequency of the demodulator is tuned to the required frequency (4.5/
5.5/6.0/6.5 MHz) by means of a calibration circuit that uses the clock frequency of the µ-controller/Teletext decoder as
a reference. The setting to the wanted frequency is realized by means of the software. It can be read whether the PLL
frequency is inside or outside the window and whether the PLL is in lock or not.
With this information it is possible to make an automatic search system for the incoming sound frequency. This is
realized by means of a software loop that alternate the demodulator to various frequencies, then select the frequency
on which a lock condition has been found. De-emphasis output signal amplitude is independent of the TV standard and
has the same value for a frequency
deviation of ±25 kHz at the 4.5 MHz standard and for a deviation of ±50 kHz for the other standards. When the IF circuit
is switched to positive modulation the internal signal on deemphasis pin is automatically muted. The audio control
circuit contains an audio switch and volume control. In the mono inter-carrier sound versions the Automatic Volume
Leveling (AVL) function can be activated. The pin to which the external capacitor has to be connected depends on the
IC version. For the 90° types the capacitor is connected to the EW output pin (pin 20). When the AVL is active it
automatically stabilizes the audio output signal to a certain level.
2.5 Video switching
The video processor (STV2248C) has three CVBS inputs and two RGB inputs. The first CVBS input is used for external
CVBS from SCART 1, the second is used for external CVBS from FAV, and the third one is used for internal video. The
selection between both external video inputs signals is realized by means of software and hardware switches.
CVBS from SCART 1, the second is used for external CVBS from FAV, and the third one is used for internal video. The
selection between both external video inputs signals is realized by means of software and hardware switches.
2.6 Synchronization circuit
The video processor (STV224X) performs the horizontal and vertical processing. The external horizontal deflection
circuit is controlled via the Horizontal output pulse (HOUT). The vertical scanning is performed through an external
ramp generator and a vertical power amplifier IC controlled by the Vertical output pulse (VOUT).
The main components of the deflection circuit are:
• PLL1: the first phase locked loop that locks the internal line frequency reference on the CVBS input signal. It is
circuit is controlled via the Horizontal output pulse (HOUT). The vertical scanning is performed through an external
ramp generator and a vertical power amplifier IC controlled by the Vertical output pulse (VOUT).
The main components of the deflection circuit are:
• PLL1: the first phase locked loop that locks the internal line frequency reference on the CVBS input signal. It is
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CHASSIS
composed of an integrated VCO (12 MHz) that requires the chroma Reference frequency (4.43 MHz or 3.58 MHz
crystal oscillator reference signal), a divider by 768, a line decoder, and a phase comparator.
• PLL2: The second phase locked loop that controls the phase of the horizontal output (Compensation of horizontal
deflection transistor storage time variation). Also the horizontal position adjustment is also performed in PLL2.
• A vertical pulse extractor.
• A vertical countdown system to generate all vertical windows (vertical synchronization window, frame blanking pulses,
50/60 Hz identification window...).
• Automatic identification of 50/60 Hz scanning.
• PLL1 time constant control.
• Noise detector, video identification circuits, and horizontal coincidence detector.
• Vertical output stage including de-interlace function, vertical position control.
• Vertical amplitude control voltage output (combined with chroma reference output and Xtal 1 indication).
crystal oscillator reference signal), a divider by 768, a line decoder, and a phase comparator.
• PLL2: The second phase locked loop that controls the phase of the horizontal output (Compensation of horizontal
deflection transistor storage time variation). Also the horizontal position adjustment is also performed in PLL2.
• A vertical pulse extractor.
• A vertical countdown system to generate all vertical windows (vertical synchronization window, frame blanking pulses,
50/60 Hz identification window...).
• Automatic identification of 50/60 Hz scanning.
• PLL1 time constant control.
• Noise detector, video identification circuits, and horizontal coincidence detector.
• Vertical output stage including de-interlace function, vertical position control.
• Vertical amplitude control voltage output (combined with chroma reference output and Xtal 1 indication).
2.7 Chroma and luminance processing
The chroma decoder is able to demodulate PAL, NTSC and SECAM signals.
The decoder dedicated to PAL and NTSC sub-carrier is based on a synchronous demodulator, and an Xtal PLL locked
on the phase reference signal (burst).
The SECAM demodulation is based on a PLL with automatic calibration loop.
The color standard identification is based on the burst recognition.
Automatic and forced modes can be selected through the I2C bus.
NTSC tint, and auto flesh are controlled through I2C bus.
Xtal PLL can handle up to 3 crystals to work in PAL M, PAL N and NTSC M for South America.
ACC an ACC overload control the chroma sub-carrier amplitude within 26dB range. Both ACCs are based on digital
systems and do not need external capacitor.
All chroma filters are fully integrated and tuned via a PLL locked on Xtal VCO signal.
A second PLL is used for accurate fine-tuning of the SECAM bell filter. This tuning is achieved during the frame blanking.
An external capacitor memorizes the bell filter tuning voltage.
A base-band chroma delay-line rebuilds the missing color line in SECAM and removes transmission phase errors in
PAL.
The base-band chroma delay line is clocked with 6 MHz signal provided by the horizontal scanning VCO.
The luminance processor is composed of a chroma trap filter, a luminance delay line, a peaking function with noise
coring feature, a black stretch circuit.
Trap filter and luminance delay lines are achieved with the use of bi-quad integrated filters, autoaligned via a master
filter phase locked loop.
The decoder dedicated to PAL and NTSC sub-carrier is based on a synchronous demodulator, and an Xtal PLL locked
on the phase reference signal (burst).
The SECAM demodulation is based on a PLL with automatic calibration loop.
The color standard identification is based on the burst recognition.
Automatic and forced modes can be selected through the I2C bus.
NTSC tint, and auto flesh are controlled through I2C bus.
Xtal PLL can handle up to 3 crystals to work in PAL M, PAL N and NTSC M for South America.
ACC an ACC overload control the chroma sub-carrier amplitude within 26dB range. Both ACCs are based on digital
systems and do not need external capacitor.
All chroma filters are fully integrated and tuned via a PLL locked on Xtal VCO signal.
A second PLL is used for accurate fine-tuning of the SECAM bell filter. This tuning is achieved during the frame blanking.
An external capacitor memorizes the bell filter tuning voltage.
A base-band chroma delay-line rebuilds the missing color line in SECAM and removes transmission phase errors in
PAL.
The base-band chroma delay line is clocked with 6 MHz signal provided by the horizontal scanning VCO.
The luminance processor is composed of a chroma trap filter, a luminance delay line, a peaking function with noise
coring feature, a black stretch circuit.
Trap filter and luminance delay lines are achieved with the use of bi-quad integrated filters, autoaligned via a master
filter phase locked loop.
2.8 RGB output circuit
The video processor performs the R, G, B processing.
There are three sources:
There are three sources:
1. Y, U, V inputs (coming from luma part (Y output), and chroma decoder outputs (R-Y, B-Y outputs).
2. External R, G, B inputs from SCART (converted internally in Y, U, V), with also the possibility to input YUV
2. External R, G, B inputs from SCART (converted internally in Y, U, V), with also the possibility to input YUV
signals from a DVD player, (YUV specification is Y= 0.7 V PP , U= 0.7 V PP , V = 0.7 V PP for 100% color
bar).
bar).
3. Internal R, G, B inputs (for OSD and Teletext display)
The main functions of the video part are:
- Y, U, V inputs with integrated clamp loop, allowing a DC link with YUV outputs,
- External RGB inputs (RGB to YUV conversion), or direct YUV inputs,
- Y, U, V switches,
- Contrast, saturation, brightness controls,
- YUV to RGB matrix,
- OSD RGB input stages (with contrast control),
- RGB switches,
- APR function,
- DC adjustment of red and green channels,
- Drive adjustments (R, G, B gain),
- Digital automatic cut-off loop control,
- Manual cut-off capability with I2C adjustments,
- Half tone, oversize blanking, external insertion detection, blue screen,
- Blanking control and RGB output stages.
- Y, U, V inputs with integrated clamp loop, allowing a DC link with YUV outputs,
- External RGB inputs (RGB to YUV conversion), or direct YUV inputs,
- Y, U, V switches,
- Contrast, saturation, brightness controls,
- YUV to RGB matrix,
- OSD RGB input stages (with contrast control),
- RGB switches,
- APR function,
- DC adjustment of red and green channels,
- Drive adjustments (R, G, B gain),
- Digital automatic cut-off loop control,
- Manual cut-off capability with I2C adjustments,
- Half tone, oversize blanking, external insertion detection, blue screen,
- Blanking control and RGB output stages.
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CHASSIS
2.9 µ-Controller
The ST92195 is the micro-controller, which is required for a color TV receiver. ST92195D1 is the version with one page
Teletext and ST92195D7 is the one with 7 page Teletext. The IC has the supply voltage of 5 V and they are mounted in
PSDIP package with 56 pins.
Teletext and ST92195D7 is the one with 7 page Teletext. The IC has the supply voltage of 5 V and they are mounted in
PSDIP package with 56 pins.
µ-Controller has the following features
- Display of the program number, channel number, TV Standard, analogue values, sleep timer, parental control and
mute is done by OSD
- Single LED for stand-by and on mode indication
- System configuration with service mode
- 3 level logic output for SECAM and Tuner band switching
- Display of the program number, channel number, TV Standard, analogue values, sleep timer, parental control and
mute is done by OSD
- Single LED for stand-by and on mode indication
- System configuration with service mode
- 3 level logic output for SECAM and Tuner band switching
IC 501 controls all the functions of the receiver operated by the remote control and the front panel customer controls. It
produces the on screen graphics, operates tuning, customers controls and engineering controls, and also incorporates
all of the Teletext functions. It also controls the video processor, the audio processor, and the tuner. The circuits just
mentioned are controlled via the I²C bus. Also IC501 controls the video source switching, vertical position adjustment
and the vertical linearity adjustment via its ports.
An external 8K EEPROM is used by the micro. The EEPROM comes fully programmed. The main clock oscillator is 4.0
MHz crystal X501 on pins 50 and 51. Reset is provided on pin 2 via Q504. On switching on pin 2 becomes high and the
controller gets reset which stays valid till a low signal comes on that pin.
produces the on screen graphics, operates tuning, customers controls and engineering controls, and also incorporates
all of the Teletext functions. It also controls the video processor, the audio processor, and the tuner. The circuits just
mentioned are controlled via the I²C bus. Also IC501 controls the video source switching, vertical position adjustment
and the vertical linearity adjustment via its ports.
An external 8K EEPROM is used by the micro. The EEPROM comes fully programmed. The main clock oscillator is 4.0
MHz crystal X501 on pins 50 and 51. Reset is provided on pin 2 via Q504. On switching on pin 2 becomes high and the
controller gets reset which stays valid till a low signal comes on that pin.
2.9.1 Controls
Command information from the infrared remote controller is fed through the sensor IC502 to pin 1 of the micro-
processor. Operation of the customer front panel keys is detected by pin 8 that is an ADC (analogue to digital
converter). Pressing a switch will connect the 5V to the ground through a particular resistor that determines the
value of the voltage on pin8 at that instant. This obtained value is comprehended by the micro and the corre-
sponding operation is performed. Refer to the following table:
processor. Operation of the customer front panel keys is detected by pin 8 that is an ADC (analogue to digital
converter). Pressing a switch will connect the 5V to the ground through a particular resistor that determines the
value of the voltage on pin8 at that instant. This obtained value is comprehended by the micro and the corre-
sponding operation is performed. Refer to the following table:
Button Theoretical
voltage
Resistance
P+
3.0V
R502
P- 4.0V
R503
V+ 2.0V
R504
V- 1.5V
R506
Menu 1.0V R505
IC501 automatically switches from TV mode to AV1 by detecting the signal from or pin8 at the Scart connector,
through it 56 pins. The picture mode is determined according to the following table:
through it 56 pins. The picture mode is determined according to the following table:
Direct Voltage
Picture mode
0 ~ 2 V
TV
4,5 ~ 7 V
16 :9
9,5 ~ 12 V
4 :3
2.9.2 Teletext
The microprocessor IC501 performs all of the Teletext functions internally. The Composite blanking video and
Sync signal (CBVS) is input to pin 33 of the micro from pin 29 of IC403. When text is selected the text graphics
are output as R.G.B signals on pins 15/16/17 of the micro and fed to pins 34/35/36 of IC403. At the same time
pin 18 of the micro goes high taking pin 37 of IC403 high, blanking the picture and selecting text R.G.B. input.
Note: mixed mode is available and fast text with 8-page memory.
Sync signal (CBVS) is input to pin 33 of the micro from pin 29 of IC403. When text is selected the text graphics
are output as R.G.B signals on pins 15/16/17 of the micro and fed to pins 34/35/36 of IC403. At the same time
pin 18 of the micro goes high taking pin 37 of IC403 high, blanking the picture and selecting text R.G.B. input.
Note: mixed mode is available and fast text with 8-page memory.
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