Sony MHC 2500 Mini HiFi system restoration

2. Sony MHC2500 HiFi system restoring – Cassette Deck, Model: TC-H500

In Sony MHC-2500 Mini Hi-Fi System the cassette deck includes two main decks, A and B, along with drive mechanisms and audio boards, enabling both recording and playback of cassette tapes. It offers features such as Dolby B and C noise reduction for clearer sound, a built-in timer, and an auto-reverse function. Instead of conventional mechanical control levers, it uses tactile switches for play, forward, reverse, and stop functions.

Deck A features a playback system equipped with an auto-reverse head mechanism and a mechanical drive board. The board features a magnetic head preamp board utilizing the UPC4570C, a high-speed and high-quality audio signal processing IC with dual ultra-low-noise, wide-band op-amps. Additionally, it includes a leaf switch coil with its drive board.

Deck B featured playback, erase record, and auto reverse head system. This deck also has the same magnetic head preamp board with the UPC4570C. In addition, it incorporates a record bias oscillator using 2SC2001 transistors, which is for cassette tape recording systems. Its primary function is to generate a high-frequency bias signal that enhances the quality of audio recordings on magnetic tape. Like Deck A, it also includes a leaf switch coil with its drive board.

Replacing Drive Belt

Deck A was not functioning due to a broken drive belt. I ordered a new 100mm belt and replaced it, which restored its functionality. However, the replacement process was a bit challenging. First, loop the belt around the spring stay as illustrated, then reposition the drive motor assembly. Using a pair of pinchers or tweezers, carefully hold the belt and loop it over the motor drive pulley.

Guide to replacing the drive belt l Guide to measure the belt

Mounting Cassette Decks

The cassette deck holder frame is used to mount Decks A and B, and this frame, along with the decks, is secured onto the chassis.

Cassette Deck Audio Boards

Audio Board A (Larger Board) is equipped with the MC14053BCP, a quad analog multiplexer/demultiplexer IC used for audio switching and signal routing. This IC functions as the AMS (Automatic Music Sensor) for Decks A and B. Additionally, the RC4458P, a dual low-noise operational amplifier, serves as the AMS amplifier. The board also features the M50964-223SP, a system control EPROM microcomputer built with CMOS technology, and power supply section.

Audio Board B features the CX20187, which provides complete stereo Dolby B and C noise reduction processing. This board also includes the MC14051BCP, which consists of analog multiplexers and digitally controlled analog switches. And the IC CXA1198AP integrates various audio processing functions, handling the encoding and decoding of audio signals according to Dolby standards, contributing to clearer, higher-quality audio reproduction. This IC also serves as the record equalizer select, allowing users to choose the appropriate equalization settings for the type of tape being used during recording.

Cassette Deck Key Board

This control panel manages the primary functions such as play, reverse, fast forward, rewind, Dolby switch, recording settings, and the cassette holder release switch, among others.

Customized Female Socket and Male Pin

I customized a 17-pin female socket and male pin for the ribbon strip wire of the main system control connection because the original components were broken and exact replacements were unavailable. To achieve this, I used a Berg strip pin and socket. The socket features 17 pins for multiple signal connections, facilitating control signals for playback, recording, and other operations.

The Sony MHC-2500 HiFi system restoring project brought the cassette deck back to life! By replacing the drive belt, securing the decks, and customizing a new connector, I restored its playback and recording functions.