On 14:50:40 hotz@jpl.nasa.gov wrote:
>>At 9:15 PM 9/8/97, wb2oyc@bellatlantic.net wrote:
Henry,
    Great stuff!  Appreciate the reply and especially since you've
filled in info that was otherwise lacking.  Being right on is a big
help too!  That is PRECISELY what is happening with the IIsi.

Paul
>
>That is certainly interesting, but I guess I still subscribe to Bill S's
>theory that it is something to do with the sense pins.  The monitor and all
>the display cards support 640X480@66 Hz, but your multiscan monitor has the
>pins set differently from the old Hi Res RGB monitor that supported that
>format and no others.  Therefore none of the older drivers understand your
>monitor and sometimes think they can't use it.
>
>You need to go poking around Apple's technical information library to get
>some of the details but what I can tell you is this:  Three of the pins on
>that 15-pin connector are sense lines used to determine the type of monitor
>connected.  In the era of the old Mac II's they only used wires to short or
>leave open those lines.  When they started coming out with multiscan
>monitors they came up with a scheme which used diodes as well so any pair
>of sense pins could have four states:  open, shorted, diode one way, or
>diode the other way, giving them 4^3 instead of 2^3  detectable monitor
>types.  Some of the inconsistancy you see may be due to the direction the
>sense lines are driven/measured since a diode will look like a short in one
>direction and an open in the other.
>
>A likely fix for you is to buy a male and female DB15 connector, connect
>all the pins except the sense pins straight through, and put the right
>shorts on the sense pins so your monitor looks like the good, old Hi Res
>RGB monitor.
>
>I don't have an Ohmmeter handy and I don't know which 3 of the 15 to look
>at or I'd measure an old monitor for you.  You'll need to get those details
>from Apple's library.  Hope you can use a soldering iron.
>
>Signature failed Preliminary Design Review.
>Feasibility of a new signature is currently being evaluated.
>h.b.hotz@jpl.nasa.gov, or hbhotz@oxy.edu