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Thread: A-trend ATC-1425A - anyone has it?

  1. #1
    Join Date
    Jul 2007
    Location
    Bucharest, Romania
    Posts
    7

    Default A-trend ATC-1425A - anyone has it?

    I got this board a few days ago and although it looks almost new, it seems someone unsoldered some parts from it... As it stands now, it is missing 6 capacitors (2 electrolytics, 4 smd) and 8 smd resistors. To have any chance of repairing it I need some close-ups of the board, and I haven't been able to find them on the net. If someone has this board, please share some photos of it. I highlighted on the attached photo the areas that are of interest to me. Many thanks!

    https://imgur.com/a/inaALYj

  2. #2
    Join Date
    Apr 2015
    Location
    Austin, Texas
    Posts
    1,026

    Default

    You have more to worry about than just missing passive components.

    The board is missing the i8042 keyboard controller and the BIOS chip. Without these, the board won't function. The i8042 is a microcontroller with internal ROM, so unless you find one from this exact board or one very similar to it, it won't work. The same goes for the BIOS chip, you'll have to find a 27c010 EPROM and write the BIOS image to it and hope it works.

    The capacitors can be worked out by what's around them. All of the electrolytic caps are the same, so just get more of those. The SMD ceramics are likely decoupling capacitors, just measure ones nearby that look the same and replace with the same value. The resistors are a bit more difficult, but can generally be worked out by what's around them. But fixing any of this is pointless unless you can get the i8042 and BIOS chip.

  3. #3
    Join Date
    Jul 2007
    Location
    Bucharest, Romania
    Posts
    7

    Default

    Thank you for your reply.

    I have both the BIOS chip and the keyboard controller, only after I photoshopped the image I noticed they are missing and didn't want to start over. The reason for that - I give each board a good scrub when I receive it, and usually remove all that is removable.

    After studying some datasheets and comparing to other boards with the same SiS chipset, I managed to find out/guess the values for most of the missing parts, but there are still a few unknowns and I feel these are enough for the board to mis-behave:

    - On the ATC-1425A there is a resistor (R68, missing/removed) that pulls up pin 126 (DIRTY/MA11/PREQ3#) of the SiS northbridge. On all my other SiS 496/497 boards, this pin only connects to one input of an 74F244 buffer, but on the A-trend it also connects to this pull-up resistor.
    - C30 and C31, two capacitors that are used as snubbers (I guess?) between northbridge pin 31 (ACLK) and GND, respectively pin 81 (CPUCLK) and GND. They are unmarked on my other boards, and I'm guessing they are in the low pF range so I couldn't measure them anyway.
    - A pair of resistors (R84, R85) that are part of the VRM, near the voltage selection jumpers. Without them, one of the settings becomes unavailable, but I still have two other choices (besides +5v) for the CPU voltage, and if I get the board working I could work out their values by trial and error / using some variable resistors in their place until I get the desired voltage.

    Other missing parts are already found out / guessed or their values are not so critical. I'm slowly giving up hope that someone will provide the photos, this board seems to be not so common and I've already PM'ed three users on different forums but they either don't respond or don't visit the forums anymore, so if anyone has any suggestion regarding my missing values...

  4. #4
    Join Date
    Apr 2015
    Location
    Austin, Texas
    Posts
    1,026

    Default

    There are pictures of this board on the net, but none are high enough resolution to be of any use.

    You should just start putting components on which you think might work, no sense in waiting forever for pictures that may or may not help.

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