Sony WM-FX435

The WM-FX433 and WM-FX435 were stereo radio cassette player Walkmans manufactured in approximately 1995 by the Sony Corporation, and assembled in Malaysia. Both units were virtually identical and this multi-page article is for the FX435 model. There were five models of this design to cater for different country regions and their radio frequency ranges. The US version was the most popular as it could also receive TV (audio only) channels 2 to 13.

• Dolby B Noise Reduction
• Three Levels of Mega Bass (Norm, Mid, Max)
• Auto reverse
• Digital Tuning and Presets
• Digital Clock
• Automatic Volume Limiter System (AVLS)
• Anti-rolling mechanism
• Dimensions: 112.8 mm × 86.6 mm × 32.7 mm
• Mass: 210 g (including batteries)

Review

This unit is based around six principle integrated circuits that form the basis of the electronic engineering. The audio pre and power amplifier IC is the LA4585M manufactured by the Sanyo Corporation. With load RL=10 Ω, and Vcc=3 V, the power output of this IC is typically 34 mW, and 10 % THD. The sound quality is excellent as always with Sanyo audio ICs, and very much depends upon the quality of your headphones that you use with the Walkman. In this early design, they use a separate IC (NJM2185V) manufactured by the New Japan Radio Corporation to provide Dolby B type noise reduction at playback. In the design of this unit, they placed the Dolby selector switch on the underside of the case.

In this unit, the tape transport mechanism and chassis design was a new direction the engineers took. The chassis is much smaller, lighter, and utilising minimal metal. There are virtually no screws, and instead plastic components are integrated into the metal chassis making it very delicate. The mechanism also uses multiple plastic cogwheels and I anticipate some broken units out there. There is also a 3-phase disc motor driven by the LB1674V IC. The design of the motor drive very much remained the same in their later designs due to the high quality performance it provided.

The system controller is the µPD1724GB, which also drives the LCD panel directly. The FM/AM, IF Amp, and MPX functionality is provided by the single-chip radio solution CXA1538N IC. If you have the US version of this Walkman, then the tuner circuitry will also have an additional IC TA7358F that provides the TV front-end functionality. My unit does not have this; hence that part of the PCB is not populated with the IC and associated components. You can see the inside electronic engineering in the following pages of this multi-page article.

Price/eBay

The WM-FX433 and WM-FX435 are very early iconic units, and I do not see them for sale often on the auction site. The cassette lid is plastic with a thin layer of paint and consequently pre-used units have a tendency to become scratched, hence a unit that is badly scratched and not working will not be worth much. However a unit in mint condition and good working order together with its accessories and packaging would be highly sought after by collectors and anyone wanting to relive their 90s youth. In this unit, the drive belt is under the main PCB, however, for an engineer, it is not too much trouble to lift the board to install a replacement belt. Hence, a unit in mint condition that simply needs a new belt would be worth a packet on a good day.

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