Graphics problem on Amiga 2000

[Argus]

Check the motherboard revision.  If it's a Rev. 4 board then someone probably did the 1MB hack to convert the 512K slow-FastRAM to ChipRAM.  There's a jumper or connection pad at the rear of the machine that you have to cut or bridge (or both) to do this.  You can find the hack details on the net (Aminet).  Perhaps the solder or cut is breaking away or incomplete.  I'd look into this because it would give the machine errors trying to access that second 512K as ChipRAM and affect graphics.  Rev 3 mb's also need a hack to fit a 2.04 or 3.1 ROM if I recall so check to see if you have the right wires and pins lined up there (should be a small wire from rom socket pin 1 to rom socket pin 31 and a second wire from rom pin 21 to bent-up rom pin 31...or something like that).  Also, make sure the Agnus chip (C=8372) is seated in its socket fully and inspect the RGB port connection to the motherboard (there could be a flaky connection there if it has been plugged in a million times).  If you could lay hands on a flickerfixer or Opalvision video slot board you could bypass the standard RGB port entirely and see if this clears the problem.

[Argus]

@Jupp3

Sounds like you have a B2000 motherboard (the American/modern design) then if you have the b/w composite out.  If it's a Rev 4 m/b or higher #, there should be no extra wires on the ROM IC.  Rev 4 boards also need the m/b hack and the Fat Agnus (8372A/B) to address the full 1MB of soldered RAM as ChipRAM.  Make sure the hack was done correctly.  I never heard of a third floppy hack (or why you'd need one with two internal and an external port).  Hopefully, the previous owner didn't fry something.  I'll do some more checking, there may be a way to adjust the RGB video port on the m/b (maybe it's slightly out of wack).