This article details the cause of the problem, gives hints on how to avoid burning the chip, and if you haven't had any luck, you'll find here instructions on how to change the PHY chip without having to send your whole computer for a logic board replacement.
Source of the problem :
In theory, Firewire supports hot-plugging. For that magic to happen, the chip is protected by a few components that will eliminate any short circuit, and flatten any voltage peaks that might happen when you connect or disconnect a device. In reality, most firewire controllers do not have those protections, meaning that they are in fact quite sensitive and fragile.
The Firewire bus does not communicate directly with the CPU, nor the logic board's chipset (NorthBridge). It is first handled by a component called PHY (for PHYsical layer), which job is to power the port itself for data to be transmitted, and to handle the communication protocol. (FireWire is derived from Ethernet, and in the same fashion an ethernet port has a PHY between the networking chipset and the physical connector on the card)
One of the main problem with FireWire is that upon connection of a device, short circuits can happen between the power pins (12-15V) and the data pins (the PHY has a voltage of 3,3V). Usually the surge protection components just evacuate the tension peaks, otherwise the PHY burns. Static electricity can also cause the destruction of the PHY.
Delicate Hardware :
The problem appeared on numerous Macs... personnally I had 2 ports give up on me in an iMac, another one on a Firewire hub, and yet another 2 on two hard drive cases. I also read somewhere that one person with a DELL laptop had the same issue.
For the Macs, Apple did the right thing and installed a solid surge protection on all recent models. However, beware if you have one of the following machines :
- Powerbook, up to the Titanium DVI (667-800Mhz)
- iBooks (at least up to the G3 800Mhz (???)
- iMac G3 DV
- PowerMac G3 - G4 at least up to the Quicksilver (???)
Special care must be taken with peripherals such as hubs and external drive cases (either hard drives or optical drives)
How to avoid the issue :
The only really proven way to avoid burning up a FireWire port is to connect all devices and to turn them on PRIOR turning on the Mac. Likely, one must unplug them and turn them off AFTER the Mac has been turned off. If you need to connect another device, then you're on for a shutdown of your machine...
It's a tad annoying but it guarantees that the FW ports won't be damaged.
Be careful when using self powered devices such as webcams, iPods, hard drives or hubs, as they can destroy the port pretty easily. Another thing is to avoid daisy-chaining hard drives.
When the FW port doesn't respond anymore :
In this case, peripherals won't be mounted upon plugging, and won't be displayed in Apple's System Profiler. The self powered devices will still be fed by the port, but won't respond either.
It happens that the PHY just hangs after a surge or a random problem. Once hung, the port will not respond any longer, it is possible to reset the component by going through the following steps :
1° boot the mac in Open Firmware by holding [ Apple key - Option - O - F ] after the startup chime.
2° you'll get to a command prompt. the keyboard mapping will be QWERTY, so pay attention when you type the following :
RESET-NVRAM (enter)
RESET-ALL (enter)
3° Now the mac should restart itself and the port should function properly again.
If it still doesn't work, then it means that the PHY is damaged.
