Dilshan R Jayakody’s Web Log

I recently had the opportunity to work on another Pioneer PL-250 turntable. The previous owner was having an issue with the platter moving back and forth without continuously rotating, which can be a frustrating problem to deal with.  After a quick inspection, I found that the issue was caused by some faulty electrolytic capacitors (3 × 470µF) near PA2005 and a bad bridge rectifier. These components were preventing the platter from spinning smoothly in the right direction. Fortunately, I had the necessary replacement parts on hand, so I quickly swapped out the bad components. Once the new capacitors and rectifier were in place, I gave the turntable a full service to ensure that everything was working as it should. After completing the repairs and maintenance, I tested the turntable and was pleased to see that it was now spinning smoothly and continuously in the correct direction.

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 ...

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...