Amiga 3000 with jerky mouse and icons switching to monochrome green

I just took possession of an Amiga 3000 with an A3640 and SCSI external box (side car) with CD-ROM drive and 3rd HDD.

The machine boots fine and fast, but mouse is jerky and erratic, to the point that I can't control it to select or close anything.

After a few random clicks of the mouse, because that is all I can do, the icons start switching to green.

Has anyone seen this before. How to fix?

Does anyone know of someone who repairs Amigas in the U.S.? Just in case, since I am not a hardware guy.

What happens if you boot Workbench from floppy? Is the SCSI box terminated correctly? The A3000s I used to use at work in the 90s would misbehave terribly with incorrect bus termination.

I had a jittery mouse recently in my A3000. The heat of various cards (most notably the Voodoo3) and the various warming/cooling cycles of turning the machine on and off caused some chips to get unsettled. I pressed on the Denise chip and now the jittery movevement is gone.

Denise is also responsible for some video functions like doing color lookup.