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Thread: MVF4S dead

  1. #1
    .
    Join Date
    Jul 2020
    Location
    France

    Posts
    5

    MVF4S dead

    Hello!

    I'm lost with this 4 slots...

    It's an MVF4S with the fast click of death.
    The PCB look great with no broken trace (i presume).
    What i have done:

    - J2 soldered for removing watchdog on NEO-B1
    - New CPU socket with new cpu (tested with x3 cpus ...)
    - New PROM socket with unibios and stock bios.
    - x4 new SRAMs

    verified HALT and reset signals (+vcc for the twos).
    vcc on each components @ 4.94V on voltmeter ~ 4.8V on my tiny scope.

    CLOCK signal seem OK (Vmax 4.1V... on last link below)

    Very strange voltage on scope for the data bus (3.1V for high state! on A15 and others). With or witthout the PROM socketed...



    74HC259 ???

    http://theangel540.free.fr/WP_20210124_009.jpg

    http://theangel540.free.fr/WP_20210124_016.jpg

    http://theangel540.free.fr/WP_20210124_017.jpg

    http://theangel540.free.fr/WP_20210124_018.jpg

    http://theangel540.free.fr/WP_20210124_019.jpg

    http://theangel540.free.fr/WP_20210124_020.jpg

    http://theangel540.free.fr/WP_20210124_021.jpg

    http://theangel540.free.fr/WP_20210124_022.jpg

    http://theangel540.free.fr/WP_20210124_023.jpg

    http://theangel540.free.fr/WP_20210124_024.jpg

    http://theangel540.free.fr/WP_20210124_028.jpg

    http://theangel540.free.fr/WP_20210124_029.jpg

  2. #2
    .
    Join Date
    Jul 2020
    Location
    France

    Posts
    5
    ... The HALT signal on the 68K is RARELY low (+vcc high on scope). sometimes he was low and i can see activity on adress bus (BIOS).
    no cut trace with HALT/RESET between NEO-B1/68K. 10uf capacitor near PST518 transistor OK. Wat the hell with this HALT :-(

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