Dilshan R Jayakody’s Web Log

The Sony ICF-SW7600GR , a well-known portable shortwave receiver, has built a solid reputation for its performance and reliability. I purchased this receiver 20 years ago, and it is likely the last portable shortwave receiver manufactured by Sony . I primarily use it for shortwave listening, and it has functioned continuously for two decades. However, like all electronic devices, it is subject to component degradation over time. This post outlines the diagnostic and restorative procedures I undertook to address a complete failure of the keypad on this radio. Restored ICF-SW7600GR radio. Initially, the radio exhibited a gradual decline in keypad functionality, which eventually led to a complete lack of response. I observed intermittent key input before all keypad operations ceased entirely. This symptom suggested a possible discontinuity or short circuit within the keypad interface circuitry. To investigate further, I disassembled the unit to inspect the internal components. My p...

Sony STR-AV780 is a combined receiver and audio/video control center. This receiver is manufactured by Sony in around 1986 and it is capable to deliver 2 × 80W audio output power with 8Ω speaker load. The STR-AV780 which I got had two problems. The first problem is in the power amplifier stage and it produces distortion in high frequencies. The second problem is in FM radio receiver and it is completely dead. The power amplifier of STR-AV780 is based on two Sanyo STK4042 XI AF power amplifier ICs. To fix the distortion issue we replace all the electrolytic capacitors in both STK4042 power amplifier boards. After replacing capacitors distortion issue got fixed and the power amplifier starts to produce a clear output waveform. The FM receiver of this AVR is mainly based on 2 ICs. For IF stage it uses LA1235, and to demodulate FM stereo signal it uses LA3401. Apart from that Sony CX7925 is used as PLL frequency synthesizer. The front end of FM tuner is based on a couple of transist...

TC-252 is 3-speed reel to reel player manufactured by Sony in around 1970 – 1972. This is transistor based tape player with 4W × 2 audio output power, sound-on-sound, and sound-with-sound recording features. The TC-252 which we got to restore had many problems. The major problem is someone alters the circuit in that recorder and attach LA4440 power amplifier into the circuit. Apart from that, the motor speed of that recorder also starts to decrease after 10min of continues playback. Other than above two major problems it had some mechanical problems in playback position and all the potentiometers in the front panel are damaged beyond repair. TC-252 main PCB after restoration. As a first step of the restoration, we remove the LA4440 module attached into that recorder and rewire the player with original wiring layouts. After rewiring we check all the transistors in that player and find out that the couple of 2SC634 transistors are damaged in that player. Because 2SC634 is not a...

TC-500 is 4 track stereo reel to reel player which is built around 1960 - 1970 by Sony Corporation. This is vacuum tube base reel to reel player with 2 × 3W audio output power. TC-500 is dual speed (3¾ and 7½ ips) tape recorder and it support reels up to 7 inches (18cm). Amplifier stage of this tape recorder is built around 12AX7, 6AU6 and 6AQ5 vacuum tubes and the 12BH7 tube is used in biasing oscillator. Other than above tubes, 6CA4 is used in PSU for rectification. Restored Sony TC-500 reel to reel tape recorder. Recently we got a chance to restore TC-500 reel to reel player which we got from our friend. The player which we got is heavily damaged and we spend nearly 2½ months to restore this player. In the first stage of restoration, we disassemble mechanical parts of this player and clean everything. In this player capstan idler wheel and take-up, idler wheel is damaged beyond repair and we reconstruct those wheels using rubber sheets.

In this project we developed 4 inputs (Audio and Video), remote control operated video switch for general home use. This design is mainly based on Microchip PIC16F630 8bit MCU, 4052 differential 4 channel analog multiplexer, TSOP1838 infrared receiver module and 7447 BCD to seven segment decoder. With a given schematic and PCB design users can switch 4 different audio and video sources using compatible remote controller. Current version of this project is work only with most of Sony remote controllers (which based on Sony SIRC protocol) and it can be easily extend to Philips RC-5 protocol with some minor modifications of PIC16F630 software system. In this design we incorporate small single transistor video amplifier to its output stages to amplify the (chroma) part of video signal. Audio output stage of this system may not need any AF amplifier. (In the designing stages we notice some clipping of input signal in 4052 analog multiplexer, but it is not much noticeable in practical e...