Oracle Jedi

Had a similar issue on a Rev H motherboard. I found swapping CAS1L/CAS1H fixed it. https://forums.atariage.com/topic/360236-atari-520st-4mb-agranlund-stram-expansion-notes-from-an-install/

Thanks for taking a look at this. Below should be the Source Summary. At this point the PC image in the background is 100% stable. 

I applied the settings from Nerdly Pleasures' blog. Basically the Sync-Type and Clock Freq. Without these the image is shaky. I think the H-Offset had to be reduced to zero...

The main menu setting. 

I don't want to declare victory prematurely, but I just set "Auto Switch" to OFF and I have a stable image, no menu. Looks great. Further testing needed....

Here's a grab of an Infocom adventure using most of the screen. This using the settings from before - the clock at 16257000 and a line length of 864. The...

I also experimented with adjusting the clock and the line length. Without much success. But I did get down to 0 PPM with a line length of 883. Auto-switching enabled...

Hi Ian, Will do.   The PC1 is back on the shelf right now but I will pull it down and try the new code.  It will be an interesting exercise...

I've applied Alpha 54E and it has helped a great deal. Upon start up the RGB2HDMI goes to CGA mode which yields a corrupted display, but manually switching to PC...