I bought an old Panasonic Sr. Parter recenty, and I'm trying to boot it off of Sergey Malinovs ISA FDC controller hooked up to a GoTek with Flash-Floppy firmware installed and with a Freedos boot disk.
Unfortunately I can't get this to work at all. I keep getting boot error 20, or boot error 40.

I'm not terribly experienced with these old PCs. I started out with PCs in the era of far more functional BIOSes, and never really understood all the various stuff you had to go through to get a secondary floppy controller working.

One thing I suspect is happening is the onboard FDC of the Senior partner might be the problem. There doesn't seem to be any way to disable it, as it's all configured via jumpers. The options for the drive are 1 disk, or 2. I'm not too sure how to configure my ISA FDC to work with the on-board one, or honestly if there's really any problem in the first place.

The other tool I have to play with is an Universal XT-IDE controller. This does seem to "see" my Gotek, and when I try to format a disk with it, the Gotek lights flash, but it just gives timeout errors.

I also have a EPROM programmer, so I could flash an entirely new BIOS, if there's something that's compatible with this old hardware.

Any help is appreciated. I'm a bit stuck at the moment, and just feel like I'm spinning my wheels trying different things, but mostly stumbling around in the dark.