Video System Theory - Lexicon RV-8 Service Manual

RV-8 Service Manual
C18 and C19 provide de-coupling for the 8.5V supply voltage that powers U2.
Output Connector (J2)
J2 is the only system-wide interface to the tuner module. A bulk supply of 12VDC is provided to the PCB
via pin 3 of J2. This bulk voltage is noise filtered by FB1. Pins 4 and 6 provide the LEFT and RIGHT
stereo signals from the tuner to the rest of RV-8, while the common return path for both of these is
2
provided by pin 5. Pins 12 and 13 provide the I C bus that controls the tuner system. RDS data is fed
P
P
2
back to the system CPU on these lines as well. R14, R15, C6, and C7 provide standard I C pull-up and
P
P
2
edge control as described in the Philips specification for I C.
P
P
MH1 is a plated-through hole that connects to Chassis Ground at the opposite end of the PCB from
LUG1. The RV-8 system provides a ground path on this pin, and by keeping it independent from the
Tuner functionality and tying it to Chassis Ground here, we ensure minimal radiated EMI from the unit.
Rail Supplies (U1 and U3)
U1 provides the analog supply voltage to the tuner module and the CRISP processor. R12 and R13
program the low drop-out regulator U1 to derive 8.5Vdc from the bulk 12Vdc provided. C17 provides bulk
de-coupling capacitance of this output supply voltage.
U3 provides the digital supply voltage to the tuner module. R10 and R11 program the low drop-out
regulator U3 to derive 5Vdc from the bulk 12Vdc provided. C16 provides bulk de-coupling capacitance of
this output supply voltage.
C21 bulk de-couples the 12Vdc driving both regulator circuits.
RV-8 VIDEO SYSTEM THEORY
The RV-8 video section consists of three major functional blocks: video switcher, video converter, and on-
screen display generator (OSD).
The video assembly consists of three boards, the Video In Board (schematic 060-15509), the Video Out
Board (schematic 060-15519) and the Video Board (schematic 060-15589).
The RCA input and output boards connect to the main board via flexible ribbon connectors, with most of
the active circuitry contained on the Video Board. Video input and output connectors are mounted directly
on the boards, which attach to the rear panel of the RV-8. Separate cables supply power and control
signals to the video assembly. Control from the main board is implemented via a serial interface.
Composite video inputs (Video In board schematic sheet 1)
Specific references are to input 1; other inputs are similar. Standard video levels applied to RCA jack J5
develop 1Vp-p is across 75-ohm termination resistor R15. Emitter-follower Q5 is located close to the
connector and buffers the input with a gain slightly less than unity. Transistor bias is supplied through
R13. Buffered video is fed to pin 10 of ribbon cable J6 through low-value series resistor R14, which
reduces high-frequency peaking in the transmission path to the video board.
Composite video outputs (Video Out board schematic sheet 1)
Composite video outputs originating on the video board are fed through individual pins of J5 to the
corresponding output RCA jacks. The on-board traces are controlled-impedance and form part of a 75-
ohm wideband transmission system, and output level is 1Vp-p when terminated in 75 ohms (2Vp-p open-
circuit).
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