The IIsi is going t need to be recapped because the caps are leaking, even if it does not look like they are. If it is working right now you might be able to do it on your own if you take your time doing it.

The IIsi has a PDS Slot similar to the SE\30 but not similar or compatible to the LC series. There is a IIsi & SE\30 PDS Slot to Nubus adapter you can put in to use a Nubus card. Just need to find it.

If you have a Mac-to-VGA adapter with dip switches, you should set it t 640X480 or 640X400 with Horizontal and Vertical Sync On and Composite on Green On. There are other settings to play with but this should work with most CRT Monitors and a few older LCD Monitors.

And welcome to the forum, Ranma Chan!