Sony CFD-G50L Boombox Repair

This Sony CFD-G50L is a notable boombox in that it doesn’t appear anywhere in Sony’s UK catalogue of the time, nor are its specs listed on any other UK website. Yet it’s a 240-volt, 50Hz model, with no provision for user-selectable worldwide voltage, and as far as I know has never left the country.

Sony Top View

Perhaps more interesting that that however is its design, which is the culmination of the so-called ‘ghettoblaster’ in its best form after decades of refinement. At a guess it would have been produced in the late 1990s or early 2000s, though I’ve seen reports of them for sale as late as 2007.

Sony Front :top Angle View

This would have been one of the last portable stereos designed to play loudly. The 2000s saw a shift towards smaller units with tiny speakers and puny amplifiers that could nearly fill a room, let alone disturb a neighbourhood. While this might not have the grunt of some of the big machines from the ‘70s and ‘80s, it still packs a significant punch. Most of this is down to Sony’s ‘Power Drive’ system, essentially a large long-throw subwoofer for which most of the case is given up as a tuned enclosure.

Sony Central Speaker

This thing will produce more base than some stand-alone micro systems of the day, and it can certainly a fill a room or two with clear, undistorted sound.

This particular example had a few faults. The CD player didn’t read discs, the tape deck warbled hopelessly off key and FM radio reception wasn’t as good as I thought it should be. Ignoring Sony’s warnings of “hazardous voltages” and “a high risk of electric shock” moulded into the bottom panel, I began resolving the puzzle of disassembly that is common to any boombox of this era. If you’re doing this on your own unit you’ll need an unusually long Philips screwdriver. Wera make a set with a 450 mm long shaft which is ideal. There are a multitude of screws recessed in the deep holes at the rear, one in a shallow depression in the base and several hidden in the CD, tape and battery compartments.

Sony Rear View

The front then comes off and there are two connectors to remove – one for the speakers and another flexible ribbon leading to the front control button board. Inside the front casing we find the three speakers, the left-most one covered by a clever moulding which forms part of the subwoofer enclosure when the case is assembled.

Inside View Of Front Of Case

A lot of work clearly went into the design of the casing of these boomboxes. This one in particular is a complex moulding and even has small slits to retain the cables which are all routed neatly around the unit so as not to inhibit airflow.

View Of Inside Case With Boards In

Two more screws at the front secure the top panel, which contains most of the electronics bar the tuner and power transformer.

Top With Main Board Fitted

I first tackled the CD player. I figured, correctly, that it would be the easiest part to repair. The lens was dusty and clouded. I carefully lifted the lens cover and cleaned the laser with a dab of isopropyl alcohol. I also cleaned the traverse rod and gears, lubricating them with a tiny drop of thin oil.

Rear View Of Top With Board

The spindle motor was stiff to turn and made a horrible rattling noise, so I lubricated it with a couple of drops of synthetic oil. I did the same for the laser traverse motor. This restored operation, mostly.

Sony Cd Mechanism

I noticed when I reassembled the machine that the CD player struggled to read some discs, in particular CD-Rs and commercial discs that were badly scratched. When I disassembled the machine for a second time for further work on the tape deck, I fractionally tweaked the laser output power by rotating the potentiometer on the back of the laser itself in a clockwise direction. Take care doing this, as if you increase the power too much you can quickly burn out the laser. A minuscule turn, hardly perceptible by feel or eye, is all that is needed and is your only option as laser replacements for anything other than the KSS-213 aren’t available. You can swap the diode itself in the KSS-151, KSS-240 and other Sony lasers as new diodes are manufactured, but it’s an incredibly fiddly procedure and it’s unlikely to be a success unless you have the factory alignment jigs or get very lucky.

Cd Drive Cogs

The tape deck appeared to be mechanically sound. The mechanism has a metal flywheel and is a self-contained unit with the playback and recording preamplifier circuitry contained within the small board on the rear.

Sony Tape Mechanism Under Side

That board has to come off to give access to the flywheel to inspect or change the belt. There’s a single screw, and some epoxy-like glue securing it to the two metal retaining tabs. This was difficult to scrape away but was eventually removed. You then bend the tabs back out of the way and pull the board free, being careful not to rip off the head wires which are soldered beneath.

Tape Mechanism Belts And Cogs

The belt had partially degraded, thinning out where it had been in stationary contact with the pulleys for a number of years. I replaced it, lubricating the capstan and motor with a drop of synthetic oil. I applied a plastic-friendly silicone grease to the exposed gears and beneath the sliding actuators on the front between the drive reels. I then reassembled the mechanism, finding that the tabs and screw were more than sufficient to secure the circuit board with no glue required.

Sony Tape Mechanism Top View

Setting the speed was the biggest challenge in this repair. When the top of the unit is fully assembled, the main circuit board covers the rear of the capstan motor. Sony didn’t provide an access hole through the circuit board to access the speed control on the back of the motor. Nor did they think to provide sufficient length on any of the cables to facilitate setting the speed with the circuit board removed.

I’d imagine these decks were set on a test bench in manufacture, but there is no such luxury for us here. In order to set the speed you need every component bar the CD player and tuner connected, but with the machine completely disassembled as there is otherwise no access to the rear of the capstan motor. It is just about possible to connect the main circuit board to the cassette mechanism, to the power transformer in the rear casing and to the speakers and front-panel controls in the front casing, all while maintaining access to the speed control on the motor. Be sure to insert your speed calibration cassette first though, as with the machine splayed open and connected in this way getting a cassette into the mechanism is all but impossible.

I set the speed using the usual 1kHz and 3kHz test tones. I was able to achieve a maximum deviation of 0.3% which is not bad for a mechanism like this. I allowed it to play for an hour or so and recalibrated the speed again, to ensure the new belt had time to bed in.

With the top half of the unit reassembled I turned my attention to the tuner. In Sony tradition the tuner is a separate module. Here it is digitally-controlled by commands from the primary system microcontroller, but is otherwise a self-contained unit. It is held in place by a plastic bracket, and when it is mounted the FM arial is a pressure connection. Attached to the FM arial is a piece of spring wire, which is formed such that when the tuner module is in place it meets with a wire jumper spanning a cutout in the tuner board.

Sony Tuner Board

The pressure of the spring wire forms a reasonably tight connection, and thus a connection to the FM antenna. However over the years the jumper had bent inward, causing an intermittent connection to the antenna and thus poor FM reception. Fixing this issue was a simple matter of bending the jumper outwards to increase its pressure against the spring wire, and reinstalling the tuner board.

This is a well-engineered electronic design. The preamplifier is based around a Sanyo LC75342 single-chip volume and tone control system, essentially a digital volume control and EQ packaged in a single integrated circuit. The cassette deck uses a TA2068N which integrates the playback and recording preamplifiers into a single IC, and the tuner also uses a Toshiba chip – the TA2749N, which is a single-chip FM / AM tuner which requires very few supporting components. It’s interesting that Sony opted to use Toshiba and Sanyo chips in their design as they still made their own single-chip preamplifiers, tape head preamplifiers, tuners and even CD laser controllers. I suppose it came down to cost, and outsourcing was cheaper than obtaining the parts from their own electronics division.

Sony Main Board

There are independent power amplifiers for the main speakers and sub woofer which output 4W x 2 and 12W RMS respectively. Sadly the markings have been removed on these chips but if I had to guess they’re probably an LM2877 and a TDA2006. There are voltage regulators for a substantial dual-rail power supply to feed the chips, and a massive heatsink that does get quite warm if you play it loud. The owners manual states that a full set of six D cell batteries will last approximately an hour at an average listening level, which is not at all surprising. This would be a very costly unit to run without a nearby mains socket.

Sony Front Turned On

And there we have it. A fully revived classic boombox that sounds quite magnificent given its relatively diminutive size. This is from a time when manufacturers were starting to cheapen some components like the cassette deck, but still cared enough to produce something that sounded good. The boomboxes you buy now are all generic and made by one of a few manufacturers in China, badged with a brand name and sold at exorbitant prices to lovers of ‘modern retro’. They sound feeble and tinny if they work at all, and they’ll be impossible to repair in years to come. Not so this Sony. It’s a genuine Sony design, well engineered with plenty of useful features and bags of power. If you find one, or a similar model and you’re in the market, grab it.

By Ashley

I founded Audio Appraisal a few years ago and continue to regularly update it with fresh content. An avid vinyl collector and coffee addict, I can often be found at a workbench tinkering with a faulty electronic device, tweaking a turntable to extract the last bit of detail from those tiny grooves in the plastic stuff, or relaxing in front of the hi-fi with a good album. A musician, occasional producer and sound engineer, other hobbies include software programming, web development, long walks and occasional DIY. Follow @ashleycox2

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