Dilshan R Jayakody’s Web Log

As an audio enthusiast, Audio-Technica has long been one of my go-to brands for reliable gear. Back in 2016, I bought a brand-new Audio-Technica AT-LP120-USB direct-drive turntable. For nearly eight years, it performed flawlessly. Then came last June. While listening to a record, I noticed a subtle drop in pitch. I adjusted the pitch slider and tried tinkering with the speed controls, but the platter responded erratically. Within a few minutes, the rotation slowed down to a crawl and came to a complete stop. Power cycling the unit did nothing to jumpstart the motor, though all the status LEDs and indicators remained brightly lit. The main logic was alive, but the motor was completely unresponsive. I decided to open it up and see if I could save my turntable. Upon opening the chassis, I was surprised by the internal layout. Rather than a simple single-board design, the LP120 utilizes a complex modular dual-PCB setup: Control board: Handles user inputs, pitch control, speed switc...

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...

Few weeks back I got Victor SEA-50 stereo graphic equalizer from one of my friend. This is 10 band stereo graphic equalizer manufactured by Victor Company of Japan (now JVC Kenwood ) around 1970 - 1980. SEA-50 consist with 63 transistors and it provides ±12dB control range for 32 Hz, 63 Hz, 125 Hz, 250 Hz, 500 Hz, 1 kHz, 2 kHz, 4 kHz, 8 kHz, 12 kHz / 16 kHz / 20 kHz center frequencies. The SEA-50 which we got is not working properly and most of its controls may generate distortion above +8dB and below -8dB. Apart from that left channel of this receiver has low volume and distortion. Defective transistors in control board (next to 2SA493). After few hours of checkup we identify few defective transistors ( 2SC982 ) in control board and we replace those with 2N3904 NPN transistors. Subsequent to this fix, all controls of SEA-50 start to work again on its full range (±12dB) by without producing any distortion or clipping.