Page Comparison

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• FDC37C651QFP Super IO controller (Floppy, IDE controller, parallel printer port and 2x serial ports)

• 2 resonators:

  • 14.31818 MHz which is not resonating because its pin1 is kept high by somethingdespite pin1 being +5V. This one seems dead.

  • 24.0000 MHz which resonates just fine.

• VL82C486: a single chip 486 controller chip which contains most logic needed for a 486 level PC:

  • 2 82C37A DMA controllers

  • 2 82C59A Interrupt controllers

  • 82C54 Timer

  • 82284 Clock generator and ready interface

  • 82288 Bus controller

  • Memory refresh controller

  • Port B and NMI logic

  • Bus steering logic

  • Turbo Mode control logic

  • Parity check and generation logic

  • Datasheet here:

    View file
    name VL82C486.pdf

• VL82C113A: SCAMP Combination I/O

  • 146818A compatible real time clock

  • 64 bytes of battery-backed CMOS RAM

  • AT compatible keyboard controller and PS/2 mouse

  • SCAMP compatible processor to ISA bus address latches and buffers

  • Datasheet here:

    View file
    name VL82C113A.pdf

• AV9155-01CW20 Frequency Generator

  • Generates clocks for 486 systems from a 14.318MHz crystal - bingo, this thing provides clocks for the CPU, sigh.

  • This is the 01 variant for 16MHz BUS

  • Datasheet here:

    View file
    name AV9155-02M20.pdf

Probing the board shows that everything is completely idle; signals on the RAM chips are mostly all high, the buffer chips visible on the board (ABT2244, ABT16245) show no moving signals - it’s dead, Dave.

The clock is clearly not there, and one reason for that is the +5V on pin 1 of the resonator. So challenge is to find out where that comes from…