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troubleshooting method for micro-controller board ?

Discussion in 'Electronic Repair' started by robb, Nov 5, 2007.

  1. robb

    robb Guest

    Thanks to all who have helped in the past too many to name ..

    seems my sacrificial chips so far were the MCU (8031) and ROM
    chip (TMM23256) :((((((( very sad

    microcontroler board , 32v and 5v rails meet. a single snap
    later and she is dead.
    5v rail to 0v rail shows 63 Ohms and should probably be about 400

    To diagnose using advice fom *s.e.b*
    removed the power regs, made a 5 Volt 1A power supply,
    connected to 5V and monitored current (~450 milliAmps) and
    monitor heat on all components

    Nothing really panned out here, no heat or crazy current

    So i removed the MCU (8031) and the super important ROM chip
    (TMM23256P) and the Ohms jumped to about ~456 Ohms and the
    current was down to ~ 275 milliAmps. so those must be the
    sacrificial chips and of course the measured Ohms of the ROM
    Vcc to Vgrd was 72 Ohms very sad : ..... ((

    so i put the 5 volt Reg back and powered up then added fuses for
    the 36 volt line and no fuses blown so now i need to get a new
    8031 replacement and a ROM chip and of course the ROM IMAGE :(((

    Semi-Good News...
    i have access to a a similar main board (an upgraded one
    actually) but it has a 8051 MCU with on board ROM and not
    external ROM

    so my choices now are
    A. get an 8051 and copy the ROM over and install maybe that will
    work ?

    B. get a 27c256 ROM chip and a 8051/8031 with or w/o ROM then
    force external memory use pin to appropriate setting and copy
    the borrowed 8051 ROM memory onto the 27c256 ... hope that works

    Any advice here and ideas are highly welcomed as i do not want to
    cause even more troubles

    thanks to all that have helped so far,
  2. Arfa Daily

    Arfa Daily Guest

    I think that it would be a good idea to restart this thread at the top of
    the list again, as it is now a long way down. The only way that I knew that
    you had posted again, was that I still had a 'watch' set on, that I had
    forgotten to remove. Just as a matter of interest, have you actually tried
    sticking the ROM (I take it that it's a standard 27 series EP-ROM ?) into a
    PROM blower just to see what it makes of it? They usually do an evaluation
    of the chip first, and will put up an error message regarding what, if
    anything, they find wrong. 72 ohms does, I agree, seem a bit low though.
    Have you compared this figure to a known good chip ? Remind me again what
    the board is out of. Is there absolutely no possibility of finding another,
    even if still in service, anywhere in the world? The 'net is a very powerful
    tool in this regard.

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