Re: Audio Reg II board smoking?

Steve,

> However, when I swapped back in the Asteroids board, R30, on the Audio
> Reg II started smoking! (Retesting with the Asteroids Deluxe board and
> the smoked Audio Reg II showed that there was no damage.)
> Unfortunately, I didn't have any schematics to Asteroids Deluxe or
> Tempest available at the time. Any guesses why I'd see this behavior?

    I don't have my schematics memorized yet, but I'm going to take
    a stab at this as being the infamous "sense resistor problem."

    Atari overdesigned their supplies and included a feedback loop on
    +5V (+sense) and ground (-sense), to account for any voltage drop
    in the wiring harness. Niice idea, but if you look at the circuit
    and then imagine the normal 5V and ground connections being
    interrupted for some reason (like, say, the ever-fail Atari board
    edge connectors), you'll notice that the power and ground can
    still get to the logic board, and very much want to...but they
    have to pass through a 1/4W resistor to do it...and they do, with
    the predictable result.

    Once you reseat the board and get the supply connections going
    good again, everything works fine, but now you have an open in the
    sense circuit because the resistor is fried.

    Fix your edge connectors, replace the resistors, and you're good
    for another couple of dozen board remove/insert operations.

    Duncan
Received on Thu Jan 8 13:21:28 1998