Failing I/O chips damaging each other?

Hello gentlemen,

While investigating 3 failed 1551 drives, I found that in two of them 
both the 6523T and the 6525 in the drive were both defective. This I 
could understand in the case of spikes, static, or careless hot-plugging 
of the peripherals. But given a failure mode where one of the peripheral 
chips fails due to old-age, are they likely to die shorting the I/O pin 
to Vcc or ground, and if so, would it be likely to damage the I/O port 
to which it's connected?

Also, as both the 6525 in the 1551 and the 6523T in the paddle take 
their power separately, and one obviously has to be powered on before 
the other, is there any any specific risk with these chips receiving 
logical high or low signals on their ports without power being applied?

regards, Rob

(fixing the 1551 paddle I will necro post on the old 6523T replacement 
thread)

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