PowerBook 17" Hardware Flaw?: GPRS PC Card Modem failures; kernel panics

Along with Jan Fuellemann of Nova Media - a Macintosh mobile connectivity solutions provider - we are investigating an issue that could prove disastrous for PowerBook 17" owners attempting to use some GPRS PC Card modems.

Fuellemann's firm tested a standard GPRS PC Card Modem used by T-Mobile and Vodafone in three new 17" PowerBooks. These PC Card Modems work properly in any 15" PowerBook, any Lombard or Pismo PowerBook. The 17" PowerBook, however, crashed with a Kernel Panic every time this kind of modem was inserted.

Essentially, it seems that Apple has throttled the allowed power consumption rate for the PC Card slot and thus may not be following exact PCMCIA standard specification cutting out the possibility to use GPRS modem cards with this line of PowerBooks.

Fuellemann also received an e-mail from the card's manufacturer, who experienced a similar problem in an IBM portable:

"According to the PCMCIA specifications, the voltage of a 3.3V PCMCIA slot cannot drop more then 10 percent as long as not more than 1 A of current is drawn.

A static test on the IBM model showed us the following:

• Without resistance, 3.25 V was measured on the PCMCIA interface (within spec).
• A resistor of 10 ohm, which compares to about 330 mA of current, made the voltage drop to 3.01V (within spec).
• A resistor of 5 ohm (660 mA) the voltage drops to 2.85V (out of spec).
• A resistor of 3.3 ohm (1A) the voltage drops to 2.72V (out of spec)

"The resistor of 5 ohm compares to what the GlobeTrotter (the GPRS modem used in this test) needs to transmit at high power, which always happens while attaching (mandatory by the network). As the voltage already drops to 2.85V in this case, this can cause the card to reset and bring a kernel panic to the 17" PowerBook."

If Apple indeed chose to use a resistance of 5 ohm or below, it may have nulled functionality of some PC Card radio phones for 17" PowerBooks.

Feedback? Late-breakers@macfixit.com.

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