Wanted!! C= a4000 silver VGA adaptor

[Ilwrath]

So, I know it won't work with my a1200 vga adaptor

Why not?  They're the same video output.  The pinout for video on the A1200 and the A4000 are identical.  Any external box should work.

That is the C= silver box pictured above...  It will work to plug any Amiga into a VGA-style connector.  

The problem, of course, would be the sync rate.  If the monitor can accept 15khz (MultiSync), or if the Amiga can output 30khz (DblNTSC/DblPAL) then you should be able to get yourself a picture, after a little tinkering around..

[Ilwrath]

But when I try and use my Amiga 4000, trying each of those modes, and making sure I have VGAOnly in my Devs/Monitors drawer it just won't play ball.

Hmm... That is rather strange.  Actually, if you are specifying Multiscan or DblPAL in the Workbench prefs, you shouldn't need to also have VGAOnly.  Maybe try it without that, once.  I seem to remember having to remove the VGAOnly on my A4000.  (I don't remember why, though... It may have just been conflicting with my CyberGraphX software)  Also, make sure you don't have overscan set for your DblPAL mode.  

By the way, how are you seeing the screen to change the WB prefs?  You have a TV or something that is also plugged in?  

The a4000 adaptor is buffered in some way, which I was hoping could just tweak the signal to allow it to output a display.

??
The C= adaptor like the one pictured above has no buffering in it.  Just an AND gate for a couple of the pins, and the rest get passed straight through.  All it does is convert the Amiga 23pin video to a VGA HD15 connector.  It doesn't touch sync.

I'm assuming it's a sync error you're experiencing.... ?