[Coco] PSA / warning for all RGB2VGA owners

[Steven Hirsch]

On Thu, 15 Oct 2015, Zippster wrote:

> Pin 9 is used in some display standards (notably DDC1 and DDC2) to 
> provide +5v from the graphics adapter to the display to read an EDID rom 
> with information about the display even when not powered.  The standard 
> calls for this rom to be powered by the display when it’s on, so there 
> is the potential that this supply could be connected to ground when 
> using the RGB2VGA board with a cable that has a through connection on 
> pin 9.

> Many, if not most VGA cables appear to have no connection on pin 9, 
> presumably for this reason.  I would guess (hope) most displays using 
> this feature would also have some kind of current limiting in place for 
> this situation, as pin 9 is shown grounded in so many pinouts.

> I have heard of no issues so far, but to be on the safe side…

Let me be the first to report an issue, then :-).  I have an older Hitachi 
LCD monitor that seemed to work only intermittantly with the rgb2vga 
adapter.  After reading your post, I checked and discovered that the cable 
I currently had attached to the monitor did indeed have pin 9 connected 
end to end.  I dug through my cable box and found a second cable that did 
not have this connectivity and, lo and behold, I now have a display on it.

I can only surmise that I had such a cable on it at those odd times when 
it seemed to work.

Hopefully you will float this pin on future board revisions.  It didn't 
appear to hurt the monitor at all, but it did prevent it from operating.

Steve


--