What is it with stereos and overload protection ?

I have AIWA stereo system 2x40W and once I
overloaded it with 4 ohm speaker (it takes 6ohm).
Before that it never turned off to a red led
but it turned off to a clock.
After that it turnes off to led randomly
even though i reseted it
(when i press power switch).

Recently I aquired Panasonic stereo system SA-AK25
2x60W that seems to be overloaded once.
MUTEA line is controled by BU2090F and it is
open drain output circuit.
When i manualy ground MUTEA stereo works.

So I conclude either BU fet is fried
or cpu somehow memories that it has been
overloaded even though I :

-reseted it with power off and drained Vcc capacitors
-reseted it While power on

Is there a secret combination of switches
I have to press to tell the cpu that now
its ok to play?

Many thanks.

Maybe you did permanent damage. Have you checked all components for evidence of overheating?

Yes I did .
I think everything else checks out.