Pioneer tuning fork Service Manual Download Page 37

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4, VIDEO Signal PROCESSING

( N T S C )

Let us see how the picked-up video signal is processed refer
ring to the following block diagram. Although the diagram
is of the 8mm VCR, its basic principles are the same as

those of 1/2" V C R s .

M a n y blocks are used in c o m m o n for recording and
playback.

Recording

(SWP)

Video

(Comb filter)

AGC

Y-C sep

Pre-

emphasis

HPF

ACC

REC amp

fs + fc

Prescaler

Sub Freq.

converter

Oscillator

(Pilot GEN)

SWP I

Phase

comparator

(/A,

fp)*

FM de
modulator

Limiter

1H delay

Comb

filter

fs + fc

+ A t

BPF

detector

/ c + A y -

Sync,
sep.

Multiplier

Prescaler

(PCM)*

Burst gate

Sub Freq.

converter

Oscillator

Phase
comparator

(Pilot GEN)*

* 8 m m VCR only

Fig. 12 Block Diagram of 8mm VCR

( / A ,

fp)*

(PCM)*

modulator

Clipper

Pre-

emphasis

Burst
up

Freq.
converter

LPF(BPF)

/ s

Burst gate

BPF

Multiplier

Sync
separator

Sync.

Playback

Video
OUT

NR, DOC

De-

emphasis

LPF

HPF

PB amp

BPF

Freq.
converter

Burst

down

ACC

LPF

De-

emphasis

Sync.

SWP

/ c +

A /

Summary of Contents for tuning fork

Page 1: ...Audio and Video Service Guide No 8 TUNING FORK PIONEER ORDER N O G G F 6 0 6 ...

Page 2: ... and PAL TV Systems 12 Measuring Instrument Pattern Generator 16 One Point Service Technique Troubleshooting Power Amplifiers after Removing Power Transistors 21 New Technique LaserVision with Digital Sound Disc LDD 23 New Products NTSC 1 2 and 8mm Home Video Cassette Recorders VCR 27 ...

Page 3: ...employed in elec tronic equipment They have only one function of open ing and closing electric circuits Their specifications depend on peripheral circuits Here we will discuss the features of metal switches and re lays employed in Pioneer products Photo 1 Switches and Relays 1 ...

Page 4: ...t is opened or closed Movable contact Fixed contact Open Closed 1 1 Material Contacts are made of silver Ag and its alloy copper Cu and its alloy gold Au and its alloy or other highly con ductive materials to make the resistance at a contact point lower than 100m12 The materials have both merits and de merits They should be used in the right place 1 2 STRUCTURE There are two types of switches push...

Page 5: ... of a power transformer Most switches are for selecting a signal and some for switching a DC cur rent Here we will discuss the switches for selecting signal channels As to the switches for opening and closing DC circuits and for sensing various conditions refer to the item 2 2 Switches Classified by Functions Switches for selecting signals usually employ the sliding mechanism which scrubs and clea...

Page 6: ...ch is capable of switching multiple circuits when switch wafers are assembled in mul tiple gangs Generally each wafer can select 11 terminals which are apart from each other by 30 This switch usually has to step over several unnecessary terminals before reach ing a desired point The contact points are of sliding type and have an ability of self cleaning With these features this switch is used for ...

Page 7: ...e locks by the first press and releases by the second irrelevant to the state of the other keys Lock release type can contain many switches deals with many circuits and does not require to pass unwanted con tact points to reach the desired point unlike the rotary switch With these features multi gang push switch of lock release type is suitable for selecting functions Switches of single and multi ...

Page 8: ... original position when the finger is released Most switches of this type have two or three contacts and two to twelve circuits The direct type is used for selecting FM de emphasis AM channel space of 9kHz or 10kHz carstereo s speakers 2 or 4 etc The indirect type is for selecting R E C P B of a tapedeck portable stereo etc Photo 4 Slide Switches d Lever switch Lever switch is basically the same a...

Page 9: ...tch or a position sensor of a mechanism Fig 6 Snap Switches and its Operating Principle Photo 6 Snap Switches Terminals Fig 7 Structure of Plate Spring Switch 7 a Open b is kept away from a when it is free b The moment of closing A and B come on the same vertical line c Closed The moment A moves further rightward the spring pushes b against a Spring f Plate Spring Switch Leaf Switch When the opera...

Page 10: ...ing and allows a large current This requires an additional mechanism to be operated because of its difficulty in manual operation This is used for switching power and selecting signal channels Fig 8 shows the structure of a typical microswitch This has one or two contacts and mostly one or two cir cuits Like the plate spring switch the number of circuits is limited The microswitch which has an act...

Page 11: ...bber directly opens and closes a part of gilded copper pattern of a printed circuit board Insulating rubber Conductive rubber Photo 9 Tact Switches i Other Switches The variations of the above switches are Flexible switch remote control switch A variation of rotary and push switches which employs a flexible wire for transmitting push pull force or torque Reed Switch This has two overlapping magnet...

Page 12: ...ue of power is used in surge killer circuits of high power ampli fiers to reduce inrush current which flows when power is turned on or in AC power circuits remote controlled by an infrared ray To withstand a high voltage and large cur rent this relay uses Silver Cadmium Oxide AgCdO at contact points The dimensions of contact pieces are larg er than those of the other to radiate heat 10 Coil Yoke A...

Page 13: ...ch a case however is unexpected because amplifier s volume control is usually turned down when power is switched on Protective relay s contact points are made of gilded silver to prevent the oxidization and sulfurization or doublepoint ed or two circuits are used for one purpose to make the contact perfect In principle the failure rate of the dual contact point relay becomes 1 X2 if that of the si...

Page 14: ...ation KHz 2 5 50 Sound Preemphasis lis 75 50 2 channel Sound Japan USA W Germany Countries Barbados Brazil Argentina Paraguay Uruguay Belgium HK Ireland UK S Africa China PR Korea PR E Germany Egypt Greece BH Iran Iraq Lebanon Libya Maulitius Morocco Saudi Arabia Syria Tunisia Bulgaria Congo Czecho slovakia Djibouti E Germany Hungary Poland Reunion Togo USSR Guyana Ivory Coast Martinique New Caled...

Page 15: ...cally unnecessary to reproduce Ei and EQ through out the frequency range of 1 5 M H Z being broadcast To make the broadcast signal compatible to monochrome and color TV receivers chrominance signal is being inserted into the vacant spaces of luminance signal in the frequency spectrum as shown in Fig 2 When a colored program is reproduced on a monochrome receiver white dots may appear due to the be...

Page 16: ...s represent ed by the following ECP Q ER EYJcosodSt b Es EY sinwst Fig 3 Bandwidth of European 625 line System for Bands IV V Channel Width 8MHz PAL receiver adds and subtracts the direct and lH delayed signals Adder and subtractor put out B Y and R Y signals respectively The demodulated signal becomes an average between the two adjacent lines Thus the resolution becomes a little lower than that o...

Page 17: ...tical retrace blanking period End of the last bottom horizontal scanning line in the 2nd field Beginning of the 1st top line of the 1st field Video carrier null level End of the 1st field Beginning of the 2nd field Video carrier null level Picture information A NTSC SIGNAL IN THE 1st AND 2ND FIELDS Field sync datum line a Burst blanking 1st Field Burst blanking 2nd Field Burst blanking 3rd Field B...

Page 18: ... center Cross hatch and dots are displayed on the same screen with LCG 399 This is for adjusting static and dynamic convergence of a color pic ture vertical and horizontal amplitude vertical and horizontal linearity and other raster alignments Center Cross For centering picture on the screen with the knobs of ver tical and horizontal position control 5 Dot 20 vertical x 15 horinzontal white dots f...

Page 19: ...Off Upper bars can be displayed on full screen with this switch depressed When 100 white is required turn the IQW on IQ signal In NTSC system the color information is broadcast on I and Q signals These signals are on the orange cyan and green magenta axes respectively for ef fective broadcasting The axes have a 90 phase difference each other PAL system uses U and V axes Ref P I 3 Fig 2 Color Bar P...

Page 20: ...before broadcasting Fig 6 Enlarged Waveform of Chrominance Signal 3 58 MHz Fig 5 Chrominance Signal of Color Bar Pattern EB EY 0 3ER Fig 7 Vector Diagram of Carrier Color Signal Red A Amplitude Y Luminance level b Non WEIGHTED C WEIGHTED Fig 8 Phasor Diagrams of Color Bars NTSC and PAL 18 Amplitude 1 3 58 jus 90 E R E Y 0 7E R Red Magenta 180 Burst Yellow Green Cyan Blue 0 90 ER EY 270 A 0 762 VY ...

Page 21: ...1 Video Level Setup Video Output This terminal puts out a composite video signal and ac cepts A 75 O BNC plug Output voltage Fixed Approx lVp p 75 Q load Variable 0 1 5Vp p 75 D load Polarity Positive negative sync signals The output is a composite signal of pattern synchroniz ing blanking and burst signals This has positive polarity with negative sync pulses to conform to the polarity of vid eo e...

Page 22: ...ect this to the external trigger input of an oscilloscope to supply it with trigger signal to display H sync or V sync signal Output impedance 75 D Accepts a BNC plug Trigger selector Selects scope trigger output frequency either HORIZON TAL or VERTICAL Fig 8 Rear panel of LCG 396 20 LCG 396 LCG 399 PAL Frequency Line 15 734Hz 15 625Hz Field Interlaced 59 94Hz 50Hz Progressive 60 05Hz 50 08Hz Outp...

Page 23: ...cal circuits of power am plifiers Driver stage Power stage Driver stage Power stage Output Output a b Driver stage Power stage B Output Fig 1 Typical Amplifier Circuits Checking method 1 Circuits a and b Fig 1 Typical Amplifier Circuit Amplifiers employing the circuit a or b can also be checked by keeping power transistors removed Output power becomes 1W or less when the emitter resistors on the d...

Page 24: ...10 Then the base current becomes 1 23mA To flow 5mA current in Q3 the current from A to should be 3 8mA To make a current of 3 8mA in Rl the potential difference between A and should be 1 26V 0 6 0 06 0 6 So Rl should be 330 O b Insert diodes in place of power transistors as shown in Fig 3 Leave Rl connected Use powerful rectifying diodes used in mains current rec tifier or open the output load be...

Page 25: ... 0 2MHz has already been occupied by two audio carriers of 684kHz and 1 066kHz as seen in Fig lb It is necessary to remove the two analog sound carriers and the second lower sideband of the video carrier to insert the dig ital sound signal in the spectrum The compatibility be tween the conventional PAL LV disc and PAL LDD disc will be lost if the carriers are removed PAL LDD discs are not being ma...

Page 26: ... Signals 2 channels EFM CIRC Encoder Video Signal Analog Audio Signals 2 channels Waveform Video FM signal Fig 3 Adding Digital Audio Signals to LaserVision Signal 24 Mixer Frequency Modulator Frequency Modulator Mixer Digital Signal Mixer Composite signal Audio FM signal Signal Limiter Optical Cutter ...

Page 27: ...d reproduction In the LDD system however feeding the phase difference signal back to the spindle motor should be avoided to prevent the sig nal from interferring the color signal To maintain the synchronization when an LDD disc is played the phase difference APCO Automatic phase con trol signal output between the reference signal generated in the player and the reproduced frame sync is applied fro...

Page 28: ...ronizes it with the suppressed pit repetition signal of the same frequency contained in the reproduced E F M signal The EFM signal contains some signals close to 4 3218MHz when the pickup is between music pieces When searching PLL circuit opens and the reproduced and generated signals become out of synchronization If the searching is terminated between music pieces the os cillation may mislock at ...

Page 29: ...l edge of audio cassette recorder ACR and television TV is essential to repair VCRs Here we will discuss the fun damentals of the 1 2 nonhi fi 1 2 hi fi and 8 mm home VCRs There are two incompatible types in 1 2 VCR 13 and VHS 8 mm Video Cassette Movie VE M800 8 mm Video Digital Audio Recorder VE D70 VHS Hi fi Video Cassette Recorder VH 600 27 New Products ...

Page 30: ...peed m sec 14 345 20 051 40 20 13 3 33 35 11 116 Writing speed mm sec 3 8 3 1 6 973 6 993 7 00 Time min 90 60 60 120 300 L 830 120 360 Video effective width mm 5 351 10 2 7 Video track width m 20 5 34 4 58 5 29 2 19 5 58 19 2 Video track angle Stop 4 5 3 6 5 0 0 0 0 5 5 6 7 4 Video track angle Play 4 5 4 1 3 2 4 5 4 5 8 8 5 0 1 4 2 5 5 8 9 9 Video recording 2 head azimuth Guard bandless Video head...

Page 31: ...g max Dubbing possible Recording system Sampling frequency KHz 31 469 2fH NTSC 31 25 2fn PAL Quantization 10 to 8 bits compression Transfer rate 368fH 5 790 M bit 1 sec Error correction Cross Interleane Code 8 words 2 parities Error detection CRCC 16 bit Modulation Biphase mark Frequency response Hz 20 15K Depends on sampling freq Distortion 0 3 W F 0 005 Dynamic range dB 80 Dubbing Addition of so...

Page 32: ...nsions and is twisted a little while audio cassette tape travels on a plane The mechanism requires high accuracy because it deals with signals of megahertz order The height and tilt of the Drum and tape guides should be properly adjusted Drum b M loading System U loading system In this system the twisting amount is smaller than that of the M loading system and the tape travels smoothly Quick shift...

Page 33: ... The characteristics of sen dust and ferrite heads obtainable when a metal tape is played back are shown in Fig 4 1 3 2 Structure of video head The structure of Video head is simple Its coil has tens of turns The narrow portion of the head top is protected by glass as seen in Fig 5 The head is fixed on a head base and is mounted on the Upper drum or Rotary disc in be tween the drums The head deals...

Page 34: ... for minimizing electric resistance and charge and for improving winding characteristic Some have a bind ing layer between the magnetic material and base Vacuum evaporation tape is made by evaporating a high retentive material and depositing it on a base in a vacuum cham ber After that a protective layer of 100A thick is formed for protecting the material against wear and corrosion Pollyester of h...

Page 35: ...low The heads lay down diagonal tracks at an angle of around 5 to the edge of the tape All tracks laid down by the A CHl head are called A CH1 tracks and all those laid down by the B CH2 head are called B CH2 tracks One A track contains one full TV field a coarse picture made with 262 5 lines NTSC and the following B track contains the next interlacing field and successive two fields compose a com...

Page 36: ...oid this the connection is performed about 7H before V sync appears or at the bottom of the screen where the A and B tracks overlap each other The heads rotates at l 800rpm to produce 30 frames 1500rpm 25 frames in PAL of pictures a second Viewed from video head Overlap Overlap Noise 1V CH 1 input CH 2 input Switching pulses CH 1 output CH 2 output Added 1 frame 1 frame Fig 10 Connecting CH1 and C...

Page 37: ...c Prescaler fc Sub Freq converter fs Oscillator Pilot GEN SWP I fs Phase comparator A fp FM de modulator Limiter fr 1H delay fs Comb filter fs fc A t BPF DO detector c Ay Sync sep Multiplier Prescaler PCM Burst gate Sub Freq converter Oscillator Phase comparator Pilot GEN 8mm VCR only Fig 12 Block Diagram of 8mm VCR 35 A fp PCM FM modulator Clipper Pre 1 emphasis Burst up Freq converter LPF BPF Y ...

Page 38: ...f emphasis is decreased as the input signal level increases to prevent over modulation The Y signal is then clipped and FMed 36 4 1 2 Y C separation The Y and C signals are separated by Y C separator to avoid intermodulation distortion because they have been in the same frequency band The input signal is added to or subtracted from the 1H delayed signal The addition and subtraction yields Y and C ...

Page 39: ...fY w Deviation Beta 688kHz 3 6MHz 4 8MHz 1 2MHz Beta Hi fi 688kHz L CH 1 38 1 53MHz R CH 1 68 1 83 75kHz 4 0MHz 5 2MHz 1 2MHz Super Beta HiFi 688kHz L CH 1 38 1 53MHz R CH 1 68 1 83MHz 75kHz 4 4MHz 5 6MHz 1 2MHz VHS HiFi 629kHz L CH 1 3MHz R CH 1 7MHz 150kHz 3 4MHz 4 4MHz 1MHz 8mm VCR 102 118 149 165kHz 743kHz 1 5MHz 150kHz 4 2MHz 5 4MHz 1 2MHz Table 5 Frequency Allocation NTSC 4 1 5 Automatic chr...

Page 40: ...he phase difference between those of the burst signal and the signal of quartz oscillator to absorb play back jitter The C signal is filtered by a 3 58MHz Band pass filter BPF and Comb filter to become pure C signal deemphasized and then mixed with Y signal 6 High Density Recording 1 2 and 8mm VCRs employ guard bandless system to save the tape Fig 21 shows video track patterns In a fast speed mode...

Page 41: ...ad sensitive to the signal on the A tracks and not to the sig nal on adjacent B tracks and on the other hand it makes B head sensitive to B tracks and insensitive to A tracks This azimuth effect suppresses the crosstalk from adjacent tracks when there is no guard band This method is effec tive to Y signal because the azimuth effect increases as the signal frequency increases Azimuth effect The pla...

Page 42: ... VCRs employ Phase Inver sion system and VHS and PAL 8mm VCRs employ Phase Shift system The fact that the signal waveforms on the two adjacent lines are almost the same to each other makes the follow ing noise cancelling process possible 7 2 1 Phase Inversion PI Fig 23 a This method records information by inverting signal phase every other horizontal period H on A tracks and Fig 24 Vertical Stripe...

Page 43: ...ous portion of pictures In the high pass filter HPF in Fig 27 the sharp edges of Y signal are differentiated and allowed to pass with high frequency noise components Their amplitude is clipped in Limiter and the input signal is subtracted by the limited high frequency signal The cut off frequency of H P F and the limiting level of the input signal is determined taking picture quality and S N into ...

Page 44: ...he error signal is also NFBed to the motor In playback the internally oscillated 3 58MHz signal is used instead of the video input signal for making the reference Drum FG PG Speed Det SWP generator Video Input V sync Sep Phase Comp Motor Drive Drum Motor RF switching Pulse 3 58MHz X tal OSC Divider PB Fig 28 Block Diagram of Drum Servo Circuit Capstan servo system In recording the capstan FG CFG s...

Page 45: ...t of Tape guide poles can be adjusted observing RF signal am plitude on an oscilloscope If the distance between Drum and CTL head of the play er is not equal to that of the recorder the reproduced V sync will be out of phase from the CTL signal and servo control will become difficult A varialble resistor Tracking VR has been employed for compensating the phase error caused by the distance error 43...

Page 46: ...l when A derails A and A comple ment each other and read a complete field 4 head system has two pairs of complementary heads The track width of the two additional heads of the 4 head VCR has been made narrow to meet slow mode tracks There fore when slowly recorded tape is played the additional heads become the main heads 11 1 Frame STILL In Frame Still the picture vibrates when the image in the or...

Page 47: ...ck signal with the B head when A head is on a B track and A track signal with the A head when the B head is on a A track The signals reproduced by the heads are quickly switched between A B and B A and are alternately taken out while they are high in amplitude Fig c shows two examples of their switching circuit block diagrams RFSWP Output of A B heads To video processor Combined envelope A B B A s...

Page 48: ...ause the audio head is stationary and the tape to head velocity is low Hi fi VCRs have solved the problem by recording audio signal through rotating heads which make the tape to head velocity high 14 1 0 Hi fi NTSC only 14 1 1 Standard p Hi fi 13 Hi fi system records audio signal on the diagonal video tracks together with video signal It shifts the Y carrier up by 400kHz and inserts four separate ...

Page 49: ...io 30 Mixer 629kHz 3 4MHz 4 4MHz FM audio 150kHz 1 3 1 7 MHz L R CH c V H S Fig 35 Recording System of VHS Hi fi VCR 15 8mm Y C R Fig 36 and Table 1 show the 8mm video tape format The top track is for auxiliary functions The bottom track is for analog audio 1 channel option The diagonal tracks are for video FM audio 1 ch PCM audio 2 ch option and tracking pilot signals a Standard recording format ...

Page 50: ...ds the output of the compara tor or 4F tracking error signal back to the capstan motor negatively In Fig 39 a if the tape slows down the head derail to the left and the level of 16kHz AfA fi f2 sig nal becomes higher than that of 46kHz AfB f2 f3 Then the level difference between the 16kHz signal and 46kHz signal is applied to the capstan motor to turn it fast Here remains a problem In this method ...

Page 51: ... heads on the Drum can erase signals frame by frame with the help of the ATF system This makes noise free editing possible 49 Tape Video PCM Head Pilot signal shifts here a When tape is slow 2 H 46 145kHz 16 407kHz 46 259kHz 16 521kHz A A A B 3 H fH X integer 1 102 544kHz 378 H 58 CH1 2 118 951kHz 378 H 50 CH2 3 165 210kHz 378 H 36 CH3 4 148 689kHz 378 H 40 CH4 lP lc 14dB 375 H in PAL RFSWP Center...

Page 52: ...ction and inter polation MOD DEM Fig 42 PCM Block Diagram 8mm CD Sampling freq 31 5KHz 44 1 KHz Freq response 20 1 5KHz 20 20KHz Quantization 10 bit ch 16 bit ch 1 0 8 8 14 modulation EFM Recorded signal Biphase mark NRZI Error correction Cross Interleave CIRC Table 6 PCM Standards of 8mm VCR and Compact Disc CIRC Refer to Compact Disc Vol 7 Bi phase mark This signal inverts at every border of bit...

Page 53: ... used for identifying the information stored by the remaining 4 bytes g PCM audio recording Pioneer has developed a compatible 8mm VCR ACR VE D70 which can also be used as a PCM audio tape deck It records for 9 hours with a 90 min tape and 24 hours with a 120 min tape 1 2 speed in PCM multi mode One vid eo track is divided into six PCM audio tracks as shown in Fig 44 and whole the tape surface is ...

Page 54: ...r field service and with news and topics in your daily life is also welcome T U N I N G F O R K N o 8 First printing 1985 Compiled and edited by Editors in Chief Norio Ichimura General Manager Product Reliability and Customers Service Division Sadahiko Yoshimine General Manager Service Department Yasuyuki Yamaoka Senior Manager Technical Information and Coordination Section and Editors Y Kojima S ...

Page 55: ...0 Airport plaza Drive Long Beach California 90801 1760 U S A P I O N E E R E L E C T R O N I C E U R O P E N V Keetberglaan 1 2740 Beveren Belgium P I O N E E R E L E C T R O N I C S A U S T R A L I A PTY LTD 178 184 Boundary Road Braeside Victoria 3195 Australia P I O N E E R E L E C T R O N I C S O F C A N A D A I N C 2100 Ellesmere Rd Suite 303 Scarborough Ontario M1H 3B7 CANADA Printed in Japa...

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