EMERSON KECRXX51, KECR2051, KECR2151, KECR1452, KECR2152 Service Manual

COLOR TELEVISION

SERVICE MANUAL

MODEL NO: - KECR1451KECR2051KECR2151

– KECR1452 – KECR2152

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CONTENTS

Safety Precautions------------------------------------------------------------------------			3
Introduction-----------------------------------------------------------------------------------			3
1.	SCART details------------------------------------------------------------------------------		4
2.	Micro-Controller and Small Signal function Æ TDA9351.------------------------		5-8
3.	Tuner------------------------------------------------------------------------------------------		9
4.	Video SwitchÆ HEF4052BP------------------------------------------------------------		10
5.	Sound Processor -ÆTDA9859---------------------------------------------------------		10
6.	Sound Output -ÆAN17821--------------------------------------------------------------		10
7.	Vertical Output Stage Æ STV9302A--------------------------------------------------		10
8.	Video Output Amplifier -------------------------------------------------------------------		11
9.	Power Supply-------------------------------------------------------------------------------		11
10. Memory IC Æ AT24C16----------------------------------------------------------------			11
11. IC Description with Pin Details-----------------------------------------------------			12
		11A. TDA9351-------------------------------------------------------------------------	12-18
		11B. HEF4052BP---------------------------------------------------------------------	18-19
		11C. STV9302A-----------------------------------------------------------------------	19-20
		11D. IC AT24C16---------------------------------------------------------------------	20-21
		11E. TDA9859-------------------------------------------------------------------------	21-23
		11F. AN17821--------------------------------------------------------------------------	24
		11G.STR5Q0765-----------------------------------------------------------------------	24-25
		11H. Video Amplifier Transistors---------------------------------------------------	25-26
12. Alignment Procedures------------------------------------------------------------------			26
		12.A. Procedure to enter Service Mode------------------------------------------	26
		12.B. Procedure to enter Design Mode-------------------------------------------	26
		12.C. White Balance Adjustment---------------------------------------------------	27
		12.D. Screen Adjustment-------------------------------------------------------------	27
		12.E. Design and Service data adjustment--------------------------------------	27-31
		12.F. Manufacturing and alignment procedures--------------------------------	32-42
13.		Block Diagram--------------------------------------------------------------------------	43
14.		Circuit Diagram-------------------------------------------------------------------------	44
15.		Track Side Layout---------------------------------------------------------------------	45

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SAFETY PRECAUTIONS

•Do not change any module unless the set is switched off.

•The mains supply side of the SMPS transformer is live. Use an isolating transformer

•Servicing of the CTV set should only be carried out by qualified person.

•Components marked with warning symbol on circuit diagram are critical for safety and must only be replaced with an identical component

•Power resistor and fusable resistors must be mounted in an identical manner to the original component.

•Discharge the capacitors like Main Filter when working on these.

•Do not solder when the set is on.

•Do not connect any external device like Speakers etc. when the set is on.

•When any signals are to be connected/ disconnected switch off the set.

•Wear rubber shoes/non-conducting so that your body does not become a passage for electric current.

INTRODUCTION:-

VE01 chassis is capable of driving 14”, 20”, 21”, 21”PF tubes at appropriate currents. This chassis is capable of working in the PAL / SECAM / NTSC systems. The sound system is capable of giving 1.5W r.m.s. output into a load 8E speaker. One page simple TELETEXT, TOPTEXT and FASTEXT is provided. The chassis is equipped with 21 pin scart connector which can accept via scart the SVHS format from VCRs.

The details of various sections with IC details and pin voltages are covered in this manual. The alignment procedure in field and also at manufacturing line is also covered in detail. The block diagram, circuit diagram and track side layout of VE01 chassis is also attached in this manual for easy reference.

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1. PERITV SOCKET (SCART)

PIN DETAILS OF SCART

Pin		Name		Description
				Audio Out Right
1		AOR
				Audio In Right
2		AIR
				Audio Out Left + Mono
3		AOL
				Audio Ground
4		AGND
				RGB Blue Ground
5		B GND
				Audio In Left + Mono
6		AIL
				RGB Blue In
7		B
8		SWTCH		Audio/RGB switch / 16:9
				RGB Green Ground
9		G GND
				Data 2: Clockpulse Out
10		CLKOUT
				RGB Green In
11		G
				Data 1: Data Out
12		DATA
				RGB Red Ground
13		R GND
14		DATAGND		Data Ground
				RGB Red In /
15		R
				Chrominance
				Blanking Signal
16		BLNK
				Composite Video Ground
17		VGND
18		BLNKGND		Blanking Signal Ground
				Composite Video Out
19		VOUT
				Composite Video In /
20		VIN
				Luminance
				Ground/Shield (Chassis)
21		SHIELD

Signal Level		Impedance
0.5 V rms		<1k ohm
0.5 V rms		>10k ohm
0.5 V rms		<1k ohm
0.5 V rms		>10k ohm
0.7 V		75 ohm
0-2 V=TV, 5-8 V=WideScreen, 9.5-12		>10 kohm
V=AV Mode
Unavailable
0.7 V		75 ohm
Unavailable
0.7 V (Chroma.: 0.3 V burst)		75 ohm
1-3 V=RGB, 0-0.4 V=Composite		75 ohm
1 V		75 ohm
1 V		75 ohm

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2. MICRO CONTROLLER AND SMALL SIGNAL FUNCTION WITH TDA 9351:- This IC is a combination of microcontroller and chroma (Small Signal function). This IC performs all important functions in TV receiver. The details of IC are bifurcated in two parts. Small Signal function and microcontroller

2A:- SMALL SIGNAL FUNCTION:

2A.1: VISION IF AMPLIFIER: The vision IF amplifier can demodulate signals with positive and negative modulation. The PLL demodulator is completely alignment-free. The VCO of the PLL circuit is internal, and the frequency is fixed to the required value by using the clock frequency of the Controller/ Teletext decoder as a reference. The setting of the various frequencies (38, 38.9, 45.75 and 58.75 MHz) can be made via the control bits IFA-IFC in sub address 27H. Because of the internal VCO, the IF circuit has a high immunity to EMC interferences.

2A.2: VIDEO SWITCHES: The video switch has one input for an external CVBS or Y/C signal. The selected CVBS signal can be supplied to pin 38, the IF video output. The selection between both signals is realized by means of the SVO bit in sub address 22H. The video ident circuit can be connected to the incoming ‘internal’ video signal or to the selected signal. This ident circuit is independent of the synchronisation and can be used to switch the time-constant of the horizontal PLL depending on the presence of a video signal (via the VID bit). Because of the availability of the Y/C input and the subcarrier output an external comb-filter can be applied. In that case an external video switch (or comb-filter with integrated switch) must be used. The subcarrier output is combined with a 3-level output switch (0 V, 4 V and 8 V). The output level and the availability of the subcarrier signal is controlled by the CMB1 and CMB0 bits. The output can be used to switch sound traps etc.

2A.3: SOUND CIRCUIT (QSS VERSION)

The sound IF amplifier is similar to the vision IF amplifier and has an external AGC decoupling capacitor. The single reference QSS mixer is realised by a multiplier. In this multiplier the SIF signal is converted to the intercarrier 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

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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 (pin 44) via the volume control. It is possible to get the AM output signal (not controlled on amplitude) on the QSS intercarrier output. The selection is made by means of the AM bit in subaddress 29H. Another possibility is that pin 35 is transferred to external audio input pin and pin 32 to (non-controlled) AM output pin. This can be realised by means of the setting the control bits CMB0 and CMB1 in subaddress 22H.

2A.4: FM DEMODULATOR AND AUDIO AMPLIFIER (MONO VERSIONS):- The FM demodulator is realised 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 intercarrier 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 which uses the clock frequency of the Controller/Teletext decoder as a reference. The setting to the wanted frequency is realised by means of the control bits FMA and FMB in control byte 29H. When required an external sound band-pass filter can be inserted in front of the narrow-band PLL. In that case pin 32 has to be switched to sound IF input by means of the bits SIF (subaddress 21H) and CMB0/CMB1 (subaddress 22H). When the sound IF input is selected the subcarrier output or AVL function are not available. From the output status bytes 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 can be realised by means of a software loop which switches the demodulator to the various frequencies and then select the frequency on which a lock condition has been found. The deemphasis 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. The audio control circuit contains an audio switch and volume control. In the mono intercarrier sound versions, the Automatic Volume Levelling (AVL) function can be activated. The pin to which the external capacitor has to be connected depends on the IC version. For the 90 degree types the capacitor is connected to the EW output pin (pin 20). For

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the 110 degree types a choice must be made between the AVL function and a sub-carrier output for comb filter applications. This choice is made via the CBM0 and CMB1bits (in subaddress 22H). When the AVL is active it automatically stabilises the audio output signal to a certain level. The signal on the deemphasis pin (28) can be supplied to the SCART connector via a buffer stage. It is also possible to use this pin as additional audio input. In that case the internal signal must, of course, be switched off. This can be realised by means of the sound mute bit (SM in subaddress 29H). When the IF circuit is switched to positive modulation the internal signal on the deemphasis pin is automatically muted. The audio switch is controlled by means of the INA/INB bits in subaddress 22H. It is, however, also possible to overrule the audio switch position by means of the ADS and ADX bits (subaddresses 28H and 21H respectively).

2A.5: SYNCHRONISATION CIRCUIT :- The IC contains separator circuits for the horizontal and vertical sync pulses and a data-slicing circuit which extracts the digital teletext data from the analog signal. The horizontal drive signal is obtained from an internal VCO which is running at a frequency of 25 MHz. This oscillator is stabilised to this frequency by using a 12 MHz signal coming from the reference oscillator of the micro controller/Teletext decoder. The horizontal drive is switched on and off via the soft start/stop procedure. This function is realised by means of variation of the T ON of the horizontal drive pulses. In addition the horizontal drive circuit has a ‘low-power start-up’ function. The vertical synchronisation is realised by means of a divider circuit. The vertical ramp generator needs an external resistor and capacitor. For the vertical drive a differential output current is available. The outputs must be DC coupled to the vertical output stage. In the types which are intended for 90 degree picture tubes the following geometry parameters can be adjusted:

•Horizontal shift

•Vertical amplitude

•Vertical slope

•S-correction

•Vertical shift

The types which are intended to be used in combination with 110 degree picture tubes have an East-West control circuit in stead of the AVL function.

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The additional controls for these types are:

•EW width

•EW parabola width

•EW upper and lower corner parabola correction

•EW trapezium correction

•Vertical zoom

2A.6: CHROMA AND LUMINANCE PROCESSING: - The chroma band-pass and trap circuits (including the SECAM cloche filter) are realised by means of gyrators and are tuned to the right frequency by comparing the tuning frequency with the reference frequency of the colour decoder. The luminance delay line and the delay cells for the peaking circuit are also realised with gyrators. The circuit contains a black stretcher function which corrects the black level for incoming signals which have a difference between the black level and the blanking level.

2A.7: COLOUR DECODER :- The IC can decode PAL, NTSC and SECAM signals. The PAL/NTSC decoder does not need external reference crystals but has an internal clock generator which is stabilised to the required frequency by using the 12 MHz clock signal from the reference oscillator of the micro controller/Teletext decoder. Under bad-signal conditions (e.g. VCR-playback in feature mode), it may occur that the colour killer is activated although the colour PLL is still in lock. When this killing action is not wanted it is possible to overrule the colour killer by forcing the colour decoder to the required standard and to activate the FCO-bit (Forced Colour On) in subaddress 21H. The Automatic Colour Limiting (ACL) circuit (switchable via the ACL bit in subaddress 20H) prevents that over saturation occurs when signals with a high chroma-to-burst ratio are received. The ACL circuit is designed such that it only reduces the chroma signal and not the burst signal. This has the advantage that the colour sensitivity is not affected by this function. The SECAM decoder contains an auto-calibrating PLL demodulator which has two references, viz: the divided 12 MHz reference frequency (obtained from the microcontroller) which is used to tune the PLL to the desired free-running frequency and the bandgap reference to obtain the correct absolute value of the output signal. The VCO of the PLL is calibrated during each vertical blanking period, when the IC is in search or SECAM mode. The base-band delay line (TDA 4665 function) is integrated. This delay line

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is also active during NTSC to obtain a good suppression of cross colour effects. The demodulated colour difference signals are internally supplied to the delay line.

2A.8: RGB OUTPUT CIRCUIT AND BLACK-CURRENT STABILIZATION : In the RGB control circuit the signal is controlled on contrast, brightness and saturation. The ICs have a linear input for external RGB signals. It is possible to use this input for the insertion of YUV signals. Switching between RGB and YUV can be realised via the YUV-bit in subaddress 2BH. The signals for OSD and text are internally supplied to the control circuit. The output signal has an amplitude of about 2 Volts black-to-white at nominal input signals and nominal settings of the various controls. To obtain an accurate biasing of the picture tube the ‘Continuous Cathode Calibration’ system has been included in these ICs. A black level offset can be made with respect to the level which is generated by the black current stabilization system. In this way different colour temperatures can be obtained for the bright and the dark part of the picture. The black current stabilization system checks the output level of the 3 channels and indicates whether the black level of the highest output is in a certain window (WBC-bit) or below or above this window (HBC-bit). This indication can be read from the status byte 01 and can be used for automatic adjustment of the Vg2 voltage during the production of the TV receiver. During switch-off of the TV receiver a fixed beam current is generated by the black current control circuit. This current ensures that the picture tube capacitance is discharged. During the switch-off period the vertical deflection is placed in an overscan position so that the discharge is not visible on the screen.

2B. - MICROCONTROLLER WITH TELETEX DECODER: - The integrated teletex decoder with embedded microcontroller is a control system designed for TV sets with analogue picture and sound control. The system also offers an on screen display (OSD) and IR remote control of all functions.

3. TUNER: - GDC Tuner EWT 5F3T1 is controlled by I2C bus through IC TDA 9361.The tuning is based on frequency synthesis tunning.

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CHANNEL COVERAGE :

BAND	OFF AIR CHANELS
	CHANEL RANGE	FREQUENCY
		( IN MHZ)
LOW BAND	E2S9	48.25 – 161.25
MID BAND	S10 – S41	168.25 – 463.25
HIGH BAND	E21 – E69	471.25 – 855.25

4. VIDEO SWITCH BU 4052: The HEF4052 is a dual four channel analog multiplexer. The main function of this device is to accept an AV input from SCART, external AV and switch the required output at pin no Z which is applied to small signal processing IC.

5. SOUND PROCESSOR: TDA 9859 is designed to perform demodulation of FM TV sound. The TDA 9859 selects signal from Three Stereo Sources or Six Mono Sources and out put can be given to scart. The sound processor is I2C bus controlled and all settings of bus are stored in sub address register.

6. SOUND OUTPUT: - IC AN17821 is used as the AF out amplifier for the Stereo application. It is supplied by 13 volts from the 13 volt DC coming from a separate winding in the SMPS transformer. An out power of 1.5 Watt can be delivered into an 8 Ohm Load. This IC is also having a feature of auto volume controller. Similarly stand by signal coming from microcontroller is used to disable the sound out put from speaker.

7. VERTICLE OUTPUT STAGE:- The STV 9302 is a vertical deflection circuit can be used for 90 degree and 110 degree deflection systems . One supply voltage for the scan is required. The drive voltage is amplified by an amplifier. The supply voltage of this IC is 15 Volts.

8. VIDEO OUTPUT AMPLIFIER: The RBG output signal from TDA 9351 is applied to video output amplifier section. IC TDA6107 or transistorized circuit can be used for video signal amplification and to be applied to cathodes of CRT for generation of R, G, and B colors. If IC

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