Sony Discman D-20

The Discman D-20 (also known as D-2 in the US and Canada) was an early portable Compact Disc (CD) player manufactured in Japan by the Sony Corporation. It was approximately 136 mm × 38 mm × 149 mm in size, and mass 545 g including batteries. Its GaAIAs laser pick-up had wavelength of 780 nm, and output power of 44.6 µW. The unit operates on four AA size batteries installed in the CD compartment below the CD. It can also accept power from a mains adapter and requires 9 V DC through the barrel socket with the centre pin negative. It also has jack sockets for headphones, line-out, and optional remote control.

Review

This was a wonderful piece of electronic and mechanical engineering from Sony and amazing to think that a well looked after unit continues to operate even today. In this unit, the CD transport mechanism consists of two widely-used and commonly available miniature DC motors (RF-300C-11440), where one motor directly spins the CD, whilst the other drives the laser sled mechanism. The mechanism for the laser sled is complex consisting of plastic cogwheels that convert the rotation of the motor shaft into a linear movement for the sled. Consequently, a broken tooth on a cogwheel usually results in a continuous ticking noise, as the sled fails to move beyond that point.

The sound quality was very good due to the M51568FP headphone power amplifier IC manufactured by the Mitsubishi Corporation. This is a fairly rare IC that I have not seen used in many Walkmans of that era. Each channel has two op-amp stages for filtering and then a final power amplifier stage. According to the manual specifications, the rated power output was 9 mW per channel with 32 Ω load impedance.

I was lucky to find a broken unit going cheap on eBay and it was not working due to two main faults. One problem was that it was not turning ON, and that was traced to a faulty micro-switch which I bypassed. The second problem was due to a broken cogwheel, and a ticking noise. I repaired these faults and also replaced the spindle motor. Hence, in the process I was able to upgrade the motor as well. In the following pages of this multi-page article you can see the photographs of the electronic engineering employed in this unit.

Price/eBay

The very early Discman CD players had a unique sound and are desirable amongst collectors for many reasons besides sentimentality. This model is fairly simple to service, and providing the laser is working, it is possible for a competent engineer to keep it going. A unit in mint condition, in good working order, with the original packaging and accessories could fetch well over fifty pounds and more on a good day; however a broken unit on its own would not be worth much more than five to ten pounds. Since parts are difficult to source, even a broken unit has some value.

This Article Continues...