Akai VS-2EGN

i 1 1
| | When C8O is absent
1 i
| {
i 1
et When C80 is present
1
1 1
Wa ot ee
The Video Judge (video signal presence/absence) detects
whether or not H SYNC is present, and acts on this in-
formation. IC22 is used for the extension of the lock
range of the AFC system.
The SYNC input from IC21 (AN5750) pin()is subject-
ed to SYNC separation to isolate H SYNC, which is
amplified by TR50, and fed to the base of TR49. On
th other hand H SYNC resulting from SYNC separation
is a DC voltage used in the phase detector, and controls
the internal VCO.
|
Lod
Fig. 7-25 Video Judge System
That is, the ouput frequency and the phase of the VCO
are locked to the input H SYNC.
Since the waveform (C) is the output from TR49, when
this voltage becomes higher than the set potential (about
switches 2.5 V) of IC20 (AN6914) pin @), output pin
(D) becomes ‘L’, and TR34 becomes OFF, ie., 12VJ
becomes ‘H’.
Since pin(6) is ‘L’, SVJ becomes ‘H’, (5V).
When there is no H SYNC, i.e., there is no video signal,
both 12VJ and 5VJ become ‘L’. (See Fig. 7-25)
2-5 REFERENCE SIGNALS IN EACH MODE (ON VIDEO PC BOARD)
VIDEO absent VIDEO present
EE PB C/R EE PB CIR
PAL: 50Hz | PAL: 50 Hz PAL: 50 Hz
REE NT: 60Hz | NT: 60Hz ve INPUTV | Nr: 60Hz VE
PAL: SOHz | PAL: 50 Hz
VEINC eee ne care ve INPUT V INPUT V INPUT V
HSYNC HP HP HP SEP SEP SEP
PAL PAL
50 Hz 50 Hz INPUT VIDEO
vipzo our | uP + SO | ups 30 Hp+vp | INPUT VIDEO | INPUT viDEO | Nt
60 Hz 60 Hz
Fig. 7-26 Reference Signals in Each Mode
‘Service Manual VS-2EGN
28