Technics SU-A600 - Service Manual

This document is a service manual for the Technics SU-A600 Stereo Integrated Amplifier, providing comprehensive information for its operation, maintenance, and repair.

Function Description

The Technics SU-A600 is a stereo integrated amplifier designed to process and amplify audio signals from various sources before sending them to speakers or headphones. It features a range of input selectors, allowing users to connect multiple audio components such as a turntable (PHONO), CD player (CD), tuner (TUNER), auxiliary devices (AUX), and two tape decks (TAPE 1, TAPE 2). The amplifier includes a PHONO MM input with a specific capacitance for turntables, ensuring proper signal matching.

Audio processing capabilities include BASS and TREBLE tone controls, which can be engaged or bypassed using the TONE control button (ON/DEFEAT) to adjust the low and high-frequency sound ranges, respectively. A BALANCE control allows for adjustment of the left/right volume balance. The main VOLUME control regulates the overall output level.

The amplifier supports various speaker configurations. It can connect one pair of speakers to the "A" terminals, another pair to the "B" terminals, or both simultaneously. Additionally, it supports bi-wiring, where the treble and bass ranges of speakers are connected separately to the amplifier terminals using two speaker cords for enhanced sound nuance and detail, reducing band-range interference. A headphones jack (PHONES) is also provided for private listening.

Operation indicators (AMPLIFIER OPERATION MONITOR) provide visual feedback on the unit's status. The "VOLTAGE CONTROL" indicator illuminates when the unit is in normal operating condition, while the "CURRENT DRIVE" indicator lights up after a brief delay, signifying that the unit is ready for operation. These indicators also serve to alert users to abnormal conditions, such as DC voltage in the output or short-circuited speaker wires, which would trigger the protection circuitry.

Usage Features

The SU-A600 offers user-friendly controls for seamless audio experience. The "STANDBY/ON" switch allows for easy power management, switching the unit between active and standby modes. Input selectors are clearly marked for PHONO, TUNER, CD, AUX, TAPE 1, and TAPE 2, enabling quick switching between different audio sources. The TAPE MONITOR button allows users to monitor the sound being recorded from either TAPE 1 or TAPE 2, or to listen to the selected source.

Speaker selection is managed via dedicated buttons, allowing users to choose between "A" speakers, "B" speakers, or both. The amplifier's design accommodates various listening preferences and setups.

For models intended for specific regions (e.g., United Kingdom, Europe, Australia, and N.Z.), a voltage selector is provided to adjust the power voltage (110 V-127 V or 220 V-240 V) according to local requirements. This ensures compatibility and safe operation across different electrical standards.

The unit also includes a cooling fan that operates at high power output levels, ensuring optimal performance and preventing overheating during intensive use. However, it is noted that some countries may not have this feature.

Maintenance Features

The service manual provides detailed instructions for maintenance and repair, emphasizing safety precautions. Before any repair, users are instructed to turn off the power supply and discharge the voltage from power supply capacitors using a 10Ω, 10W resistor. After repairs, the primary voltage should be slowly applied using a power supply voltage controller to verify consumed current in NO SIGNAL mode.

The amplifier incorporates a protection circuitry designed to prevent damage from conditions like short-circuited speaker wires or speaker systems with impedance lower than the rated value. If the protection circuitry activates, the unit will not produce sound, and the "CURRENT DRIVE" indicator will not illuminate. Users are advised to switch off the power, identify and correct the problem, and then switch the power on again.

Disassembly instructions are provided with clear steps and diagrams for removing various components, including the cabinet, front panel assembly, volume P.C.B., operation P.C.B., tone amp P.C.B., power switch/headphones P.C.B., rear panel, power transformer P.C.B.s, power supply P.C.B., chassis base, and fan motor. Special attention is drawn to sharp edges on chassis components during disassembly and servicing.

Instructions for replacing the power IC are also detailed, including cutting joints, unsoldering pins, and applying compound grease between the heat sink and the power IC for proper heat radiation. The importance of tightening screws sufficiently after replacement is highlighted to ensure effective heat dissipation.

The manual also includes a comprehensive replacement parts list, with components identified by a "mark" having special characteristics important for safety, such as fire-retardant resistors, high-quality sound capacitors, and low-noise resistors. Users are advised to use only manufacturer-specified parts for replacement. Wiring connection diagrams, schematic diagrams, printed circuit board diagrams, a block diagram, and a function of IC terminals are provided to assist technicians in troubleshooting and repair.