Pioneer tuning fork Service Manual page 32

The features of VCR not found in A C R are as follows:
a) Broad frequency bandwidth ( D C - 4 . 5 MHz)
b) Helical scanning system for achieving high tape-to-head
relative velocity
c) The frequency bandwidth of Y-signal compressed by
frequency modulation(FM).
d) C-carrier down-converted to achieve easy phase control
High frequency signal is liable to be affected by jitter
which causes color distortion.
e) Guard-bandless double-azimuth scanning system to
achieve high density recording
f) Phase Invert (PI) or Phase Shift (PS) system to reduce
C-signal cross talk
Drum
Loading ring
S reel
(a) U-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 shifting of the functions and view­
ing pictures in F F and R E W mode is possible because the
tape is threaded right after loading.
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Guide roller
H
Capstan
Guide roller
T reel
Full-erase-head
Drum
(c) Simplified Tape Path
Fig. 1 Tape Transport Mechanism
1. Structure of V C R
VCR consists of a tape transport mechanism, a drum scan­
ner, video-, audio-, control- and erase-heads, electronic
circuits for processing TV signal and servo control systems.
1 . 1 T A P E TRANSPORT M E C H A N I S M
Fig. 1 shows the M-threading (VHS) and U-threading (13)
mechanisms. The tape is pulled out of cassette and wraps
a half of the periphery of the tilted d r u m . It travels in 3
dimensions 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 D r u m and tape-guides should be properly
adjusted.
Tilted post
Guide roller
S reel
(b) M-loading System
M-loading system: The tape length required for threading
is shorter t h a n that of U-loading system although twisting
is larger. Shifting functions takes 2 or 3 seconds because
threading is made after P L A Y is depressed. Video heads
and tape wear well because the tape does not touch the
heads in F F and R E W modes. However, Picture Search
is made after threading.
Audio-head
Capstan
Tape
Pinch-roller
Control-head
Drum
Tilted post
H
Guide roller
Capstan
T reel