I often see Subwoofer Units at flea markets available very cheap. Very likely the main unit was broken and the repair deemed economically infeasible to the previous owner. An additional bonus with these SubWoofer Units is a secret knowledge that an average flea broker does never possess – to switch on, the unit waits a certain signal from the missing main unit. This way, these SubWoofers often get marked as “not working”.
The reason I have bought this particular one, was the price:
Of course it was, because such a subwoofer weights a couple of kilogramms, has a big 100W transformer inside plus two amplifier chips. Philips MC288 / 12 SubWoofer contains one TDA7264 chip for both left and right channels (2x 25W) and yet another TDA7265 chip bridged for a small 8 Ohm 50W woofer.
The unit actually has another, smaller transformer, inside, intended to provide the some voltage for the CPU of the main unit.
As said, I obtained the lone subwoofer. Now the main question started to transform into a simple idea – to mimic the “start” signal for the SubWoofer unit. With some clever googling, two service manuals were discovered, one in English, another in Spanish. This way, I had the schematic in possession to make the decisions. I am really trying hard not to make Philips sad on copyright issues (and you googling hard), thus I only represent the part of the scheme one will need for the decision making and even that with a nonsense resolution.
The blue rectangle is the Holy Grail, the second PSU providing the standby voltage. And, the green line is the lifeline carrying the voltage. The pink wire is waiting to be energized for transistor Q501 to open and let the power reach both the amplifier chips. Last but not least, if your aesthetics prescribe a more gradual startup sequence, the red MUTE line is responsible for precisely what the writing says. Here is the pinout for the connector you should tap into:
Putting it very short, on the output connector, pins 4&5 need to be shorted then magic will happen. The event is illustrated below by the dark pink, well, the violet wire. As you see, I tried hard to keep all the original wiring intact.
The original cover for the connector compartment was glued inside .. could need someone needs it at later times. And, a new cover was hand made from a random piece of Acryl.
This is what the fresh cover looks like:
Mission has been completed. My new toy is currently passing the burn-in test.