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Sun Nov 13, 2016 10:53 pm

magnetic ethernet jack? what it does?

Sun Nov 13, 2016 11:05 pm

hi all. thanks for having this forum so i can ask this question, because either google is broken, or i just don't know the proper terminology to search for. feel free to read the long story, or reply to the short!

short version:
i have tested an ethernet jack on a G4 iMac (circa 2001) and noticed pins 1,2 and 7,8 show continuity to each other. i also tested a 2010 mac mini ethernet port to corroborate that: lo and behold, continuity between pins 1,2 and 7,8.

why is this, and how to defeat it?

long version:

i am rejuvenating a 2001 G4 iMac (yes the lampshade one!) i am putting a 2010 mac mini inside of it.
i've completed the TMDS to DVI conversion, tested and operational!
i cut off the IO portion of the logic board, and am soldering headphone cables, usb cables, etc to the OEM ports so that all plugs on the back are original AND functional.

i did the power button, headphone, mic, and just finished making my connections to the ethernet jack. verified no shorts on my job with a microscope. it doesn't work though.

router plugged into cable soldered to IO board, patch cable from there to laptop: "network cable is unplugged"
router plugged directly into laptop with same patch, all is well.

this is where i began to check for shorts with my MM. i realized pins 1,2 and 7,8 show continuity with each other respectively.
i then took the mac mini logic board and tested the pins inside the jack, and found the same result.
i have ripped every component off of this logic board short of the jacks, and 1,2 no longer show continuity, but 7,8 persist.

this logic board is clearly multiple layers with full and partial vias, so i figured somebody could help me understand how and why this is done, and in turn i could devise a simple way to defeat it.

thanks in advance for reading this and offering your advice.

PS if you're unfamiliar, the iMac G4 has a round base, and the IO jacks are fanned out in a semi-circle. this is why i'm not making my own IO board to mate with the chassis holes.

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