After fitting a D.K. Video Crisper RGB video buffer, which I hear is 15khz only; to the RGB port of my A1200 OS 3.9, before a Scandex doubler, I have no video signal; HDD activity stops, about when WB is loaded in startup.
I am using an external Scandex doubler to TFT monitor for both CGA and VGA modes. I tried a second Scandex and no change.
The Early boot menu shows but invisible mouse pointer. Floppy boot is the same.
From this thread:
https://forum.amiga.org/index.php?topic=73237.0 I followed Oldsmobile Mikes' suggestion of swapping the ROM's for new ones and Accelerator card and PSU. Also disconnected mouse and Joystick. No Change unfortunately.

Suggestions Welcome. TIA.