Philips MC-151/12 Micro System Repair Fail

You can’t save ‘em all. This is a late model micro ‘hi-fi’ system from Philips, one of the last models to include a cassette deck before systems of this style fell out of fashion. In truth to call this ‘hi-fi’ is misrepresentation as it is ‘low-fi’ at best and ‘no-fi’ more accurately, but for a simple shelf system where sound quality is of no concern it will do the job, albeit poorly in every respect. It’s a far cry from the once-great audio division of Philips who produced the first cassette recorders, a myriad of portable and hi-fi turntables, one of the first consumer CD players and even owned Marantz for a time. Heck without Philips, Bruno Putzeys might never have had the opportunity to develop his UCD amplifier technology, which later evolved into the NCore amplifiers which are some of the finest class D amplifiers available today.

Front View Complete

There were three complaints on this one. An extremely noisy and intermittent cassette deck, a skipping CD player, and the unit would randomly cut out and restart itself. 8 screws give us access to the inside; essentially a single circuit board and generic CD and cassette mechanisms.

Top Of Main Board

On initial receipt I had visions of dealing with a faulty switch-mode power supply as the system weighs a touch over 1.5 kilograms which is almost nothing. I was surprised, and pleased, to see a transformer and linear power supply.

Rear Of Front Panel Tape In

I tackled the cassette deck first. This was ultimately the reason this machine was eventually scrapped as I couldn’t get it to function reliably, and it turned out that the single-chip head amp was actually faulty. This is a typical mechanism probably made by Tanashin or Alps, I’m not sure which. It is playback only. The mechanics are all there to implement a record function, as is the space for a button on the front panel, but the head is playback only and there is no erase head. This is as cheap as it gets. I covered the motor repair in a separate article, which you can read here.

Underside Of Main Board

This removed virtually all of the motor noise. I then removed and cleaned the two belts with isopropyl alcohol, and packed the gears at the front of the mechanism with white grease.

Top Of Tape Mechanism

The mechanism ran quietly and its speed stability was greatly improved. I set the speed with a 1kHz test tone and moved onto the CD player. I would later discover that the chip responsible for amplifying the signal from the tape head was faulty. It would intermittently drop channels and emitted an intermittent scratching cracking noise, like the noise you hear from a failing transistor. I’ll confess I didn’t even try to find another.

There were two issues with this CD player, which uses standard Sony KSS-213 laser optics. The first was a stiff and noisy spindle motor. I added a drop of synthetic oil down the motor shaft into the top bearing and spun up the motor using an external power supply, which loosened it up and got rid of the noise. I did the same for the laser drive motor, just in case. I then cleaned the laser drive bar and gears, and lubricated them with a tiny drop of the thinest, lightest oil I had on hand. You don’t want to add too much oil here, as the oil can easily attract dust and worsen the problem.

Underside Of Cd

I then cleaned the laser with a cotton bud soaked in isopropyl alcohol, moving in circular motions having slid the end of the cotton bud gently beneath the automatic lens cover. I used a small air blower to remove any residue and dislodged dust. The CD player was now cured. Replacements for this laser are available for about £4, and replacements for the entire mechanism block for £9.99. As with the aforementioned head amp chip, this system isn’t worth the cost of either.

Rear Of Front Case Tape Out

The final issue had me stumped for a while. The system would randomly cut out, though only for half a second. It would always switch back on, but no amount of cajoling could cause the issue to occur at will. There were no cracked solder joints on the mainboard, and none of the power supply components produce any significant heat. It was then that I noticed the plug which consists of a European two-pin plug fitted into a UK plug adapter.

This is standard fitment on a lot of Philips equipment, and the design of the plug adapter means it is permanently mounted. As it turned out, the plug adapter was making poor contact. Thus the system would temporarily lose power, just long enough for the system to shut off but not long enough for the power to fully drain, hence the system powering back on after the power loss.

Its performance is worse than you might expect for a system like this. Even cheap micro systems of the day sounded decent enough and some of them, especially the mid ‘90s and early 2000s models, were actually quite sophisticated. Not so here. The amplifier which outputs a mere 2 watts RMS per channel, has a 60dB A-Weighted signal to noise ratio and as a result a prominent hiss. You can hear the sound of the system microcontroller and even the sound of the laser motor through the speakers too, and especially through the headphones.

Rear View Complete

I don’t have the original speakers but I can’t imagine they were anything to write home about. The unit is designed to drive speakers of 8 ohms impedance or higher which is sensible. The power supply simply wouldn’t have enough headroom to drive a lower impedance load without clipping, even at a mere 2 watts per channel. All in all it sounds adequate and gets loud enough to fill a small room, but that’s about the best that can be said for it.

This Philips system has nothing in its favour other than its simplicity. Far from the best micro system ever built; units sold under supermarket or department store brands were vastly superior in every way. If I saw one for free in mint condition I wouldn’t pass it by, but there any number of better systems to spend your hard-earned cash on. It was scrapped for its parts including the motors, a few of the working chips, voltage regulators, small transistors, sockets, switches and the power transformer.

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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