1)Any amplifier channel pulls current through the SOA_PROTECT line for long enough to charge up capacitors C5871 and then C5872 so that Q5874 turns on.

2)Any amplifier channel pulls current through the OVERLOAD line for long enough to charge up C5882 and turn on Q5882 and thus Q5884.

3)Any amplifier channel has a large long term (DC) offset (typically greater than +/-3V) sμFficient to charge up C5861 enough to turn on either Q5862 (positive offset) or Q 5864 (negative offset). These then turn on Q5863. N.B. This circuit is also used to detect imbalances in both the Vcc/Vee

and +/-15V power supplies (the latter is generated on the Power Supply board).

4)When the PTC thermistor TH585 mounted at the top centre of the heatsink gets sμFficiently hot (around 100C) and thus high resistance enough to cause Q5855 to turn on via the +12V supply. Intermediate temperatures will not activate PROTECT but will provide signals to the level detec- tors associated with the FAN_1 and FAN_2 lines, to run the cooling fans at high or low speeds respectively.

Note that the fans’ 12V supply is gated via Q5909 and Q5911. This means the fans will not run when no signal is present on the FL, C or SR channels, so that during quiet passages no fan noise should be audible.

AVR400 Main Power Supplies Circuit Description

The main DC power supplies are located on the Power Supply Board - a double sided PTH PCB adjacent to the Main Board. Note that the mains input switching, mains fuses, standby power transformer with its associated unregulated DC supply and the relay for enabling the power amplifier supply rails are located on the Main Board. The two boards communicate via CON501.

Considering the Main Board first, the mains voltage switching uses a double pole double throw slide switch accessible from the back panel. One pole addresses the standby transformer and the other the toroidal power transformer. Ensure the switch setting matches the supply voltage before switching on the AVR400. Nominal settings are 115 and 230V +/- 15%. The 20mm 115V fuse in line with the toroidal trans- former is rated at 15A T (Time delay) and the 20mm 230V fuse is rated at 8A T. Always replace these fuses with the same type and value. The standby transformer T5941 is not fused but is designed to go open circuit in case of overheating (e.g. if left connected to a 230V supply for longer than a few minutes when the mains voltage selector is set to 115V).

The standby transformer generates approximately +9V DC via the bridge rectifier diodes D5495/6/7/8 and the 1,000μF reservoir capacitor C5947.This is sent via pin 7 of CN501 to the Power Supply PCB (confusingly marked as 5V). The rail voltage is also routed to the system microprocessor (μP) via D5965/ R5965 and pin 6 of CN103 as POWER_MUTE.

The 5V relay RY594 is normally open. When the mains switch is closed then the SUB_POWER rail (approx +4.3V) is activated from the Power Supply PCB via the standby transformer. When the system has booted correctly, without any shutdown signals, then the POWER_RELAY signal from the system μP also goes high, pulling down Q5947 hard. Only then does the relay close and switch on the main toroidal power transformer, enabling the rest of the system to boot up.

Now consider the Power Supply Board, found on page 14 of the schematic. This generates all the main DC supplies for the AVR400 except +Vcc and -Vee for the power amplifiers and the non-logic part of the VFD display requirements of the Front Panel Board. Note that additional local regulation also takes place on the other PCBs, e.g. for large digital ICs.

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Arcam service manual AVR400 Main Power Supplies Circuit Description
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AVR400 specifications

The Arcam AVR400 is a high-performance AV receiver designed to provide an immersive home theater experience. As part of Arcam’s esteemed lineup, the AVR400 combines advanced technology with exceptional sound quality, catering to audiophiles and home cinema enthusiasts alike.

At the heart of the AVR400 is its impressive power amplification, providing 100 watts per channel across 7 channels, ensuring a robust performance capable of driving a wide range of speakers. This power output is complemented by a high-current design, which means the receiver can handle dynamic audio passages without distortion, offering clarity in both subtle and explosive soundtracks.

One of the standout features of the AVR400 is its support for various surround sound formats, including Dolby TrueHD and DTS-HD Master Audio. This allows for an unparalleled audio experience, transporting users right into the heart of the action. Additionally, the AVR400 is equipped with the latest HDMI inputs, ensuring compatibility with a multitude of high-definition sources, including Blu-ray players, gaming consoles, and streaming devices.

The AVR400 also boasts advanced video processing capabilities, supporting 4K pass-through as well as upscaling of lower-resolution content to 4K. This makes it an ideal choice for users looking to future-proof their home theater setup, as it can seamlessly integrate with modern 4K televisions while enhancing the quality of older content.

User-friendliness is another essential characteristic of the Arcam AVR400. It comes equipped with an intuitive on-screen menu system that simplifies the setup process. The inclusion of an automatic calibration system helps optimize speaker settings in accordance with the room acoustics, ensuring users achieve the best sound possible from their setup.

Furthermore, the network features of the AVR400 allow for streaming audio from various online services and wireless devices. Built-in support for DLNA enables users to access their media library wirelessly, while the USB input allows for direct playback from flash drives or external hard drives.

In terms of build quality, the Arcam AVR400 embodies the brand’s commitment to excellence. With a sleek design, high-quality materials, and an engineered chassis that minimizes vibration and interference, the AVR400 is not only visually appealing but also built to deliver performance over time.

In summary, the Arcam AVR400 is a feature-rich AV receiver offering a perfect blend of power, precision, and versatility. Whether for movie nights or music listening, it stands out as a reliable choice for those seeking high-quality audio and video reproduction in their home entertainment systems.
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