If I boot without extensions, the display stays mirrored and I can use the machine but - obviously - this isn't of any use to me. However, anytime I try to boot with various combinations of extensions enabled, as soon as it finishes booting, the mirroring stops. (I get about a second where I can see the desktop and then the external monitor goes dead).
Let's look at this logically…
1. NO extensions = everything is fine. This means the hardware and VGA system work.
2. Various extensions ON = Display blanks after boot. Clearly, SOMEthing in the software is causing the display to quit.
What first jumps to mind (mine at least) is your Mac seems to be exhibiting a behavior NOT like a Wallstreet. A Wallstreet has mirroring
only at the video out - both VGA and S-Video. There shouldn't be anything that would "kill" the display at boot completion. Other, similar G3s, like the Bronze or Pismo, have extended OR mirrored capability and have a Control panel and a Control Strip that can switch that.
So, for starters: Are you absolutely certain you have a Wallstreet there? They all have identical video outputs.
Next, since you CAN get it working with extensions off, it's clear that at least one of them is causing the problem - either by its mere presence, its settings or causing a conflict. So, your next step is obvious…possibly tedious, but with good possibility of success.
1. Boot with extensions off.
2. Using Extensions Manager, set "OS9 Base only" and reboot. If no screen, reboot Extensions off again and goto
#3 - If screen works, goto
#53. Using Extensions Manager, set "OS9 Base only" - make a list of all checked extensions. Now look for and disable anything that has the words "monitor", "display" or anything that might be display-related and the Control Strip Extension then reboot. If screen works, check each one you eliminated one by one until you find the culprit. If it's the Control Strip, goto >System Folder/Control strip Modules< and remove anything video-related. Reboot. If screen works, goto
#4.
4. Something caused a conflict causing the mirrored display to fail. Start using the machine, adding back extensions only as needed into your new "My extensions" set. Rename that set so you keep track.
5. Compare what's active in "Base Only" and whatever the "normal" set is (default name is "My Extensions although it may have been changed) and add the additional ones back in one by one, rebooting each time (I did say tedious) until you find the one causing the problem. Build a new default set without it (if it's vital, holler back with the name and we'll go further).
Somehow, this
will work for you. I can't explain it any better or further because I'm even having trouble keeping
myself from getting lost.
What matters is that it IS absolutely extension-related - otherwise the screen wouldn't work at all. Finding the culprit extension can be tedious, OR you can combine logic and luck and find it very quickly. The on;y saving grace is you only have to find it
once.