At 9:15 PM 9/8/97, wb2oyc@bellatlantic.net wrote:
>On 17:50:33 hotz@jpl.nasa.gov wrote:
>>>At 3:12 PM 9/8/97, wb2oyc@bellatlantic.net wrote:
>>
>>Are you using an Apple-brand video cable?  There are some sense pins that
>>must be set to inform the display drivers what resolutions are possible.
>>
>Well yes, since the cable is permanently attached to the monitor, and it is
>an Apple ......
>
>>Virtually every display driver ever made for a Mac should support this I
>>would think.
>>
>Driver maybe, but my question is why doesn't it work at all with various
>video cards, including the builtin video output from the IIsi??  One would
>think an Apple monitor should work on an Apple computer, right?  Since
>it works on the IIci, and any other Apple video card I have here also.  Hmmm
>wait a minute, thats not totally true!  There is one, really old, Apple HiRes
>card with only 256K of memory on it, and it doesn't work on that either!
>Later models of that same card are fine, and so is that one if I put in more
>memory (I know, cause I took it out to put it on another later card that had
>only one bank).  Thing is, that later card worked fine, but only 16 colors
>until I put the second bank in.  But this one doesn't work at all now
>with that monitor with only one bank full.

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.

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h.b.hotz@jpl.nasa.gov, or hbhotz@oxy.edu