November 16, 2009 AT 12:18 pm

Fixing motherboard COM port dongles

mboardcom

So remember that Shuttle computer we got a few weeks ago? Finally had time to install it as our backup shipping station and we couldn’t get the scale to work (its a serial port device). Turns out the motherboard “COM port dongles” were wired for a different kind of motherboard! So if you ever decide to do this yourself, note that the dongles come with ‘alternating’ pins when they really should not be. Check your motherboard documentation to verify which you need, and then a quick soldering fix!

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5 Comments

  1. I had the exact same issue recently with a BioStar A760G M2+ AM2+ board.

    I chalked it up to being: a) I had a generic connector, and b) they probably sell a board specific version. I couldn’t find a board / mfr specific version, so I did just what you illustrate!

    Fortunately the manual usually provides the pinouts…

    Mike Y
    Dallas, Texas

  2. Difficult to see what the dongles are doing, I am thinking that they link the 9 pin header (10 with 1 NC) to the outside female connector.

    If so, perhaps it is best to make it clear that the photo you show is correct for your motherboard specifically…

    I use an Asus Motherboard and recently had to make up a similar cable to fix a Dreambox that I bricked. On my motherboard, the straight through arrangement is the correct version to use. Apparently there is not a standard serial pinout on motherboards.

  3. Don’t know ’bout all them new-fangled serial ports on motherboards but I definitely had IDE/Floppy/Game/Parallel/2xSerial ISA boards which had different wiring of the ten pin headers for the serial ports so the separate back-plates with 1×25-pin and 1×9-pin serials weren’t interchangeable.

  4. Motherboard and expansion board manufacturers (and anyone else that’s paying for labor) commonly(?) make their header pinouts line up so that IDC connectors on a ribbon cable will get the right signals on the right pins at the D connector. That uses the alternating conductor scheme from the Bad ribbon in the photo. My guess is Adafruit got a “free-range” motherboard, or one from a vendor who wants you to buy only their cables.

  5. Loved the economic evaluation of computer options. I just built a Celeron dual core for my daughter for less then 350, here in Brazil. My kids simply doesn’t need a core i7… in fact neither do I. My AMD Athlon 64 is beginning to feel slow, but will last until at least next year, when I’m getting a core 2 duo or an Athlon X2

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