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6. SERVO/SYSCON CIRCUIT OPERATION
1) Summary
• When power is applied to the TV/VCR. The Servo-Syscon 1 chip confirms the operating mode of the deck
mechanism, via the CAM SW. If the mechanism is not in it's initial mode, the capstan motor will advance the
mechanism to the proper position, depending if a tape is present or not. The deck is now ready to receive ser-
ial data from the timer IC.
•
The Timer IC determines which function button has been pressed either on the unit or by the remote sensor.
Then the timer IC sends data to the Syscon IC to initiate the selected mode of operation.
• When loading a tape, the L/C motor, capstan and drum motors are activated momentairly until the tape is
threaded around the drum. This must occur before a normal screen will be observed.
• The drum servo system keeps the picture in sync both horizontally and vertically, by controlling the drum speed and
phase.
In PB mode the D-PG is compared against the reference signal, if required a error signal is sent to the D.PWM.
This will correct for speed errors.
• Capstan servo system controls, the speed and phase of the tape. This prevents distorted audio and elimi-
nates noise bands on screen. In addition it helps prevent a lot of on screen noise caused by tracking prob-
lems. Capstan control is accomplished by comparing the CTL signal, measured from the lower section of the
A/C head. The Syscon IC then computes the error signal which is then sent to the C-PWM.
2) VCR OPERATING MODES
(1) EJECT
(2) STAND-BY
(3) STOP
(4) FF
(5) REW
(6) REC
(7) PAUSE
(8) PLAY
(9) STILL
(10) CUE & REV : MODE that allows a tape to be searched in the forward or reverse direction.
7. NORMAL AUDIO CIRCUIT OPERATION
1. REC Mode
The input is applied to pin 16 of IU01 and is amplified by the Line Amp., through the ALC circuit. One output at
pin 22 connects to the speaker. The second output through the REC AMP., pin 21, connects to the R/P head
and 70KHZ bias oscillator circuit.
2. PB Mode
The audio signal from R/P head is input to pin 2 where it is amplified and equalized, then the signal is directed
by the #1, SW to the appropriate mode. In normal mode the audio signal is once again amplified by the Line
Amp. and re-directed to the TV.
8. VIDEO CIRCUIT OPERATION
1. EE mode
In EE mode video is applied to pin 31 of IY01 then it is output at pin 28. By the time the signal reaches the video out-
put terminal, it's amplitude has increased 2X by the AGC and video amp.
: MODE that a cassette ejects from the compartment.
: MODE that a cassette is unloading.
: MODE that a cassette is loading.
: Fast Forward MODE that moves the tape forward from the STOP mode
: REWind MODE that moves the tape reversely from the STOP mode
: RECord MODE that records video and audio signal on the tapes.
: record PAUSE MODE that makes recording stop.
: MODE that plays the record tape
: play STILL MODE that playback is paused
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