My A500 Rev 5a (I think, the one with B52 Rock lobster on the board), required me to solder a Jumper from Pin 1 to 31 on the 2.04 ROM when I purchased it. If I remember correctly the machine still booted before I hooked up the jumper, but there was no video output. But the memory ain't that clear these days so I could be wrong on that.
I'm fairly sure I had to remove the wire when I replaced the board with a Rev 6.
:-D
