If they both stop at exactly the same time then there's nothing wrong with the speakers - probably a "common" fault somewhere in the Technics box - I would suspect some kind of heat related fault possibly in the area of the power supply.
There are techniques you may wish to use to discover the location of the problem - one is to use freezer spray in an attempt to cool the defective part and make the fault go away - another is to use a hair dryer to bring the fault on quicker.
Selective application of heat and cold may help you to locate the circuit area and then the circuit component that's failing.
You may consider putting the box in the fridge for a few minutes to see if it makes the fault go away quicker - this will tell you if it really is a heat problem. Take care of not getting it too cold else condensation in a warm room may cause other problems.
Peccavi
June 2010
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