It is difficult to say without knowing the full history of the unit.
Possibilities are that the power supply fault took the chip out through over volting the 5 v rail. That's bad news because it means other chips on that supply could be damaged as well.
Other possibilities are that the 74HC86 chip failed and that is what took the power supply out.
Also if someone else has worked on this then they could have done something like shorting a higher voltage rail to the 5 volt rail causing damage.
So lots and lots of possibilities but impossible to guess because of not knowing what the original failure was.
Possibilities are that the power supply fault took the chip out through over volting the 5 v rail. That's bad news because it means other chips on that supply could be damaged as well.
Other possibilities are that the 74HC86 chip failed and that is what took the power supply out.
Also if someone else has worked on this then they could have done something like shorting a higher voltage rail to the 5 volt rail causing damage.
So lots and lots of possibilities but impossible to guess because of not knowing what the original failure was.
