Dilshan R Jayakody’s Web Log

Pioneer PL-250 is direct drive auto-return turntable with the s-shaped tonearm. This turntable is manufactured by Pioneer in around 1979 - 1982. The PL-250 which we got had many electronic and mechanical issues. The main electronic problem in this unit is it's varying speed. The speed controller of this turntable is based on PA2004 and PA2005 ICs. After checking each an every electronic component in speed controller PCB, we figure out that the problem is in the " Pitch Control " potentiometer (VR1) of this unit. After replacing VR1 with 5K (log) potentiometer, the speed problem got resolved and the motor starts to spin with correct speed(s). Servo motor and speed control assembly of Pioneer PL-250 turntable. The turntable which we got comes with original Pioneer cartridge with "broken" stylus. We test several cartridges with this player including cheap US $ 3.00 cartridges (which are available on eBay), Audio Technica AT-91 and Audio Technica AT-95E ...

This quick post is to introduce " HTML5 Mandelbrot Generator ", which is a simple JavaScript application to generate Mandelbrot set and Julia set fractals in HTML5 compliant web browsers. This application is derived from Mandel source code (which is available at http://www.cylog.org ) and it covers most of the features available in that original application. The online version of this HTML5 Mandelbrot Generator is available at https://dilshan.github.io/mandelbrot-js . Few fractals generated with "HTML5 Mandelbrot Generator" are shown below: Mandelbrot and Julia set fractals generated from "HTML5 Mandelbrot Generator". All the source code of this application are available to download at https://github.com/dilshan/mandelbrot-js under the terms of MIT Licenses .

This is a quick post to showcase 100W 4 channel AF dummy load which we build to test the output stages of audio power amplifiers. This dummy load use 4, 8Ω 100W wire wound resistors which are available on eBay . In this unit, all 4 resistors are mounted on 170mm × 40mm × 60mm high gauge aluminum heat sink. A prototype version of the 100W AF dummy load. It costs LKR1200 to build this unit and the most expensive component in this unit are wire wound resistors. At the time of writing these 100W resistor packs are available on eBay for USD $6.00.

TX-7700 is AM/FM stereo tuner manufactured by Pioneer in around 1975 - 1980. This is a basic tuner system which is specifically designed for " rack style " stereo systems. Compare with other tuner systems this tuner is not very popular and very limited information is available on the internet about this model. This tuner is mainly built around HA1138 AM radio receiver, HA1156 stereo decoder and PA3001 (HA11225) FM IF amplifier IC. The TX-7700 which I got is manufactured for Japan and because of that it is designed to work with 100V AC and frequency range is limited to 76MHz to 90MHz. In this quick post, we demonstrate how to tune this stereo receiver to 88MHz to 108MHz by without modifying the circuit(s) of the tuner. In this tuner, the main component which needs to adjust is 5 turn inductor located in FM front end circuit (refer A in below photograph). The frequency range of the tuner can be adjusted by changing the spacings of this inductor. If tuning is getting dif...

When working with an expensive speaker system, speaker protector is an essential item to avoid any damages to speakers. In this project, we build a low-cost speaker protector by using NEC's μPC1237 IC. The circuit in this project is based on μPC1237 datasheet and it is specifically modified to work with 24V AC power source and with the 24V relay. Prototype version of μPC1237 - 2 channel speaker protector system. PCB design of this project is limit to 90mm × 43mm and based on through-hole components. Depending on the supplied voltage and relay, the value of R7 resistor is needed to be changed. The specified value in the schematic is for 24V AC power source and for Omron 24V G2R-2 relay. Start-up delay of this unit can be adjusted by changing the values of R5 and C5. Schematic and PCB design files of this project are available to download at google drive .

CoCA "Emerge + Tech" - Musical plants is an electronics, software and plants base exhibit we developed for Cinnamon Colomboscope 2016 exhibition. This installation will feature a touch-sensitive sensor that will generate a soothing sound from each plant. By interacting with individual plants, the audience can create musical compositions. The sensor unit of this project consists of 14 high sensitive, configurable level detectors and USB interface. In this sensor unit, we use Samsung's KA2284 as an amplifier, level detector, and PIC18F4550 8-bit MCU as data multiplexer and USB I/O controller. PC817 optoisolators are used to interface between analog front-end and digital data processor. In this design, both analog and digital circuits are physically and electronically isolated to minimize the noises and interferences. In this design, we use KA2284 because it is commonly available in the local market (in Sri Lanka) and costs less than 0.1 USD. To reduce the interfer...

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.