[Ti] Firewire Port Frying External Hard Disks

[Kynan Shook]

I didn't notice until starting my reply that you were writing from an  
IEEE E-mail address...  It all makes sense now.  ;-)  Most people  
don't go that far in tinkering.
Honestly, I can't say much that will help you; cables are also a  
common culprit.  One company went as far as replacing all their  
firewire cables every several months to avoid internal shorts between  
power and data lines (the most common cause of a fried Firewire  
device).  And, believe it or not, it *is* possible to plug a Firewire  
cable in backwards, despite the keying.  It just takes a little extra  
force.  Barring those two easy solutions, there's not much I'm aware  
of that will help.  I forget exactly which revision (yours was either  
the last without it, or the first with it, IIRC), but they started  
adding protection diodes and other circuitry to the Firewire circuit  
on the PowerBook motherboard to reduce the number of port failures.   
The only option I know of to fix the motherboard is to replace it.

I would agree with your assessment that it doesn't seem like the  
PowerBook has the power available to be the culprit, despite the  
evidence to the contrary.  Though a 3.3V source through a 100 ohm  
resistor is a good 33 mA, which is more than many ICs can handle if  
they are internally shorted to ground.  In any case, a new firewire  
cable, and a PC Card for the PowerBook might be the best solution to  
avoid frying any more Firewire bridge chips.

Jerry Krinock <jerry at ieee.org> writes:
> After burning up several external Firewire hard disk enclosures in  
> the last
> couple months, I've finally found a possible pattern: I believe it  
> happens
> whenever I connect one of them to our old 867 MHz Ti Powerbook G4.   
> Upon
> connecting an external drive to this old Powerbook, I hear a  
> snapping sound
> inside of the external drive case, smell some faint smoke, and when  
> I take
> the drive case apart I often see that the case of the Firewire  
> interface IC
> has a crack or a hole it it, and this seems to be the source of the  
> smell.