Barco GRAPHICS 1209S, Руководство по обслуживанию

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Date : 10/02/98 R7621127
Sync+Vertical Deflection R7621127
17
Technical description
consequently the latter is used as sync stripper for all modes except Video / SVID.
An automatic detection circuit drives two gating diodes in order to guide the sync from
the LM1881 to the TDA2595 or to bypass this one.
1. By means of the "V sync" stripped from the composite sync
The "VID/HS/CS" from the "RGB INP + SW" module is capacitively applied to pin
2 of the sync stripper IC4, and to the emitterfollower Q6 on condition D10 is forward
biased.
The separated sync pulses at pin 1 go through R55 and D9 to the same
emitterfollower on condition D9 is forward biased.
Whether the TDA2595 is used or the LM1881 as sync separator, depends on the
condition of the gating diodes D9 / D10.
The composite video mode is detected as follows. The OPAMP 5 - 6 - 7 in IC9 acts
as a level detector (no feedback). The video is integrated at the pin 6 input and pin
5 is fixed at a threshold level with R156/R157. For composite video the output pin 7
switches low which results in a saturation of Q7 and thus a blocking of D9.
D16 and D17 are then both forward biased via the stabistor D21. Consequently, the
line oscillator is forced at the minimum (15 khz) and the "Freq Mode" is also forced
to the lowest range.
The HS/CS' output of the sync stripper goes to the base of Q8 of the coincidence
detector and the COMP input of the PPL IC6.
The vertical positive pulses from IC2 pin 9 (VS) leave the main unit and arrive on the
subunit at the base of Q418. In order to find these pulses at the collector, Q415 must
be conducting to form a ground return for the emitter.
As long no vertical pulses arrive on Q416’s base, the latter is not conducting and
Q415 is turned on via the R509 resistor connected to the +5V line.
2. By the vertical external sync
The vertical oscillator can also be synchronised by VS EXT pulses, separate vertical
sync pulses injected into the projector at the VS input. Such pulses can also be
delivered by the optional “HDTV Sync interface” if mounted on this unit. The “VS EXT”
pulses are inverted by Q416 and trigger the oscillator via D425. The same negative
pulses at the collector also charge up C478 to an average low level cutting off Q402
in this case.
c) “Bella”, a Barco customer made IC
The voltage or waveform, applied between VRP and VRN is adjustable in 128 steps
and becomes available at the corresponding VO output. The corresponding pins of
such a potentiometer are :
VRP1 : “positive side” of the potentiometer “1”.
VRN1 : “negative side” of the potentiometer “2”.
VO1 : variable out (slider) of potentiometer “1”.
Notes :
1. If the signals applied to above inputs are negative and positive with respect to the
supply, then, the VSS pin (14) must be supplied with a negative voltage.