AV8 Video Board

Introduction

The L922 board is the video and I/O board for the AV8 preamp processor. This board and its snap off contain the video multiplexing for composite, s-video and component/RGB video switching as well as two On Screen display (OSD) chips, one for the main room and one for Zone 2. The PCB also has the SPDIF digital input multiplexing, RS232 connector, 12V triggers for zone 1 and 2, RC5 input for zone 1 and 2, RC5 output and the program button for reprogramming the micro controller flash memory.

The main video signal is not fed via OSD chip, instead the OSD signal is generated synchronised to the incoming Video and then cut into the video using a high speed multiplexer. The only part of the display that comes from the OSD chip is the text and its background.

This technique avoids the whole picture going soft whenever text is displayed however it introduces significant extra complexity.

Video PCB Icons + Mechanical Refer to circuit diagram L922 sheet 1

This sheet contains drawing symbols to enter items on the run out BOM as well as the chassis fixing points and their associated EMC decoupling capacitors.

Video Board Top

Refer to circuit diagram L922 sheet 2

This sheet shows the interconnections between the different sheets within the Schematic Hierarchy. It also shows the snap off for the Headphone connector.

Video Board

Refer to circuit diagram L922 sheet 3

This snap of PCB contains the composite video inputs the composite multiplexer and the composite outputs and their mute circuits. The video inputs are 75R terminated then AC coupled to the inputs of two RHOM BA7625 5 : 2 multiplexers. These multiplexers have a gain of 2 (i.e. 6dB) expect to be AC coupled at the input and DC coupled at the output, if the input is inadvertently DC coupled it will shut down as the bias network will not operate. This could happen if any of the coupling caps are dc short at the input.

IC 200 is the main signal path multiplexer. Output 1 from the main multiplexer IC200 goes to the main PCB via the buffer IC203 and SK209 to the OSD chip. IC 202 is the VCR videotape loop it is buffered by IC203 then AC coupled and connected via a 75R series termination resistor to the RCA phono connector SK201.

IC201 is the Zone 2 multilexer output one from this is fed via the buffer IC203 and SK209 to the main PCB where it goes to the Zone 2 OSD chip.

The Buffer chip IC203 is a BA7623 video driver chip from RHOM, it expects to be DC coupled at the input and AC coupled at the output. If any DC current is drawn from the output the chip will shut down as the output bias network

will not work. This could happen if any of the output caps are DC short.

The monitor 1 and 2 outputs and the Zone 2 output are fed directly from the main PCB via SK209 to the 75R series termination resistors, after the termination resistors are the mute transistors which pull to ground to shut down the output. This only provides about 20dB of mute however this is enough to shut down the sync so that a monitor will not recognise that a signal is present.

The multiplexers are controlled via the serial to parallel conversion latches IC204 and IC205. These are programmed by a 16bit data word. The clock for the data is (Video Serial CLK A) and the DATA is (Video serial data A), once all sixteen bits have been clocked into the latch the data is passed to the outputs by clocking the latch signal video comp latch.

Screen Display

Refer to circuit diagram L922 sheet 4

This sheet contains; the on screen display chip for the main zone 1, the input multiplexer for the onscreen display chip to select which type of video source to send to the OSD, the clock oscillators for PAL and NTSC generation, the clock multiplexer to select PAL or NTSC for each of the zones, the RGB output buffers and sync on green insertion, a sync separator and mono-stable to generate a black level clamp signal.

IC301 selects the input signal from the composite, S video or Y/G inputs, this signal is buffered by Q300 divided by two by the two 75R resistors then AC coupled into the input of the On Screen Display chip IC302. It is also possible to route the output of the OSD chip itself via this multiplexer to the input of the sync separator so that the black level clamp can still operate when the OSD chip is generating RGB or YUV signals.

IC302 is the On Screen Display chip it generates the text patterns which are multiplexed into the video using the fast blanking signal. Fast blanking is asserted whenever there is activity on the output of the OSD chip. The chip is programmed via a serial bus made up of the lines Video serial data, Video serial clk and Video serial cs. The Horizontal line lock is performed by a Phase Locked loop internal to the OSD chip the filter components for which are R349, C349 and C350.

LESCREEN input sets the screen intensity for the background and LECHAR sets the Screen intensity for the Characters. The potential dividers on the pins define the voltages.

The composite output of the OSD chip is sync tip clamped by the circuit made up of Q302 Q304 and D300. This circuit pulls the most negative part of the signal to a fixed voltage, in this case approximately 0v.

The sync tip clamp works in the following way. A fixed voltage of approximately 1.2v is generated by D300 and the 4K7 current limiting resistor R343, this holds the base of Q304 at 1.2v which in turn holds the base of Q302 at 0.6v. If the voltage on the collector of Q302 goes 0.6 v below the voltage on the base (i.e. below 0v) the darlington pairQ302 and Q304 turns on and dumps charge on the coupling capacitor C348 until the voltage is increased to 0v. So the most negative part of the signal always remains at 0v, the most negative part of a composite video signal is the sync and hence this is pulled to 0v.

This sync tip clamp circuit is used for all of the composite signals so they are all clamped to the same level. This

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Arcam AV8 Video Board Top Refer to circuit diagram L922 sheet, Video Board Refer to circuit diagram L922 sheet

AV8 specifications

The Arcam AV8 is a high-performance audio-video receiver that has garnered attention for its exceptional sound quality and versatile features, making it a sought-after option for both audiophiles and home theater enthusiasts. Designed to provide an immersive viewing experience, the AV8 is equipped with a range of technologies that enhance its performance.

One of the standout features of the Arcam AV8 is its support for high-definition audio formats. The receiver can decode various lossless audio formats, including Dolby TrueHD and DTS-HD Master Audio, allowing users to experience studio-quality sound. This capability is complemented by its advanced digital signal processing, which ensures that the audio output is clear and dynamic, enhancing the overall entertainment experience.

The AV8 is built with an emphasis on connectivity and flexibility. It boasts multiple HDMI inputs and outputs, facilitating seamless connections to a variety of devices such as Blu-ray players, gaming consoles, and streaming devices. With support for 4K video pass-through, the AV8 is future-proofed for high-definition content, ensuring compatibility with the latest video technologies.

Another notable aspect of the Arcam AV8 is its user-friendly interface. The receiver is equipped with an intuitive on-screen display that simplifies navigation and setup. Additionally, Arcam has incorporated room calibration technology, which analyzes the acoustic properties of the listening environment and adjusts the audio output accordingly. This feature allows for optimal sound reproduction, tailored to the specific characteristics of the room.

The build quality of the AV8 is exceptional; it features a robust chassis designed to minimize vibration and interference, ensuring high-fidelity sound reproduction. The receiver is designed for ease of use, with remote control functionality and smart home integration options, making it convenient to operate alongside other devices.

In summary, the Arcam AV8 is a powerful AV receiver that combines high-definition audio capabilities, extensive connectivity options, and user-friendly features. With its strong emphasis on sound quality and innovative technologies, it stands out in the competitive landscape of home theater equipment, catering to the discerning tastes of audio enthusiasts and casual users alike. Whether for music or movie playback, the AV8 offers a compelling solution for those seeking an elevated audio-visual experience.