Solving a Apple Airport Base Station Mystery
We have a winner!
Gustav Thullner identified the fried transistor on François Rayer's modem card. Despite the lack of identifying marks, Gustav knows it is a NPN Silicon High Voltage Transistor, type BFN18 made by Infineon. Many thanks for digging out that information! Now François has the pleasure of sourcing the transistors, removing the old ones, and soldering the replacements in place. Given the trouble of finding a modem card, this may still be preferable!
Anyway, for the sake of posterity, I have kept the rest of this page intact. Thus, here is François Rayers's original letter:
No problem with power supply in my three ABS over here, but I encountered some trouble with the modems. This appeared only on early "European ABS", my friends with US version did not notice the burn out of the transistor managing the "on/off the hook" function of the modem.
I had two of the three modems which doesn't work correctly anymore. As you'll see on the attached pictures, it heated a lot ! It's not a big deal to replace the burn out transistor... assuming you know which reference it is. I failed in my search for the schemes of this modem (the same as the Pismo Powerbook by the way) and Apple does not want to provide this info to its loyal customer.
Might you have some helpful info for solving what the name of this @#!@# Q2 transistor? This will help me to find a stronger replacement part and, I hope, cheaply and durably fix my two ABS.
Here is a picture he sent of the burnt transistor:
Toasted Transistor on Modem Card
I have no idea what transistor belongs in there. I have some pictures of my modem card that might help others identify the transistor in question.
Detail of Transistor on my Airport Base Station modem card
Bottom View of my Airport Base Station Modem card
Top View of my Airport Base Station Modem card. Area of transistor highlighted in red (top right corner).
Initially, I postulated that the space next to the transistor was for a heat sink that was never fitted. Chad Jones kindly corrected me:
It looks like a dual footprint to me. What that means is the engineers put two different footprints down for the same component in the design. During product test the must have (incorrectly, it seems) concluded that they could use a smaller part (and, hence, save money). I would suggest to Françios that he find a part with identical specs to the BFN18 but in the bigger package that would fit the other footprint on the board. This bigger package will have better thermal properties and should not give out on him like the smaller part did.
And so, we once again show the promise and power of the Internet... A question that came up in France is answered by experts on the other side of the globe. Many thanks to everyone that helped. Cheers!
Constantin