Re: A3000 and A4091

CyberDez wrote:
Daniele Gratteri ha scritto:

Also, if you better read the post, you'll see that the
A3000 SCSI controller works fine, he has problems with the added 4091 one.

Hello Daniele,
yes you're right: the problems are with the A4091 (that works flawlessy
in a 4000D) not with the onboard A3000 Scsi controller.
Looking around the net about a possible solution I suspect that A4091
need a Ramsey -07 too, not only a SuperBuster 11, when used in a 3000D.
But as all serious Amiga user knows, this means a replacement for the
DMac too. I found that those two chips are quite rare (expecially the
Dmac -04) and expensive so I would buy them only if I'm sure they will
fix those problems with A4091.
Someone told me that if the onboard A3000 scsi chain is left empty some
malfunctioning occours in other parts of Amiga, the floppy drive for
example, maybe the Zorro DMA too?
Yes, I plan to upgrade the WD33C93 chip to a rev. -08 too but in the
main time I would fix (if possible) this issue between the A4091 and the
As additional info, the ROMs on the A4091 are the latest available:
rev. 40.13

Best regards and thank you for joining the thread :-)


There are several reference files on the Web that explain this. In
short, the A4091 was never recommended for the A3000. It might work,
might not. Your right about the need for a Buster 11. The basic need
for the trio (Buster 11, Ramsey 07, DMAC 04) concerns the A3640. Here
is some of the excerpt, I edited it to answer your question, so please
read thru it carefully.

by Oliver Knorr, 1997-12-28
Kickstart 2.04 ROMs
These are 'normal' AmigaOS ROMs, that do not require booting a
Kickstart file.The newer A3000s were delivered with these ROMs. These
ROMs will work with the A3640, except if you have the combination of a
RAMSEY-04 chip (which almost any A3000 has) and static column Fast-RAM.
In this case, you need to exchange the SCRAM at least in bank 0 with
page mode RAM chips or (even better) upgrade to AmigaOS 3.1 ROMs. You
can not upgrade the RAMSEY to the new rev. 07 (which would also fix
this problem), because for this you would also need a DMAC-04, which
is not available anymore.
The RAMSEY and DMAC chips are important A3000 custom chips that, among
other things, implement part of the A3000's onboard DMA SCSI host
adapter. Nearly all A3000 were delivered with the revision combination
of DMAC-02 and RAMSEY-04. The problem with this combination is, the
DMAC-02 does not like 68040 boards like the A3640. There are both heat
and timing problems. If you are lucky, the tolerances of your DMAC-02
are wide enough to work together with the A3640. If you are not so
lucky, SCSI will not work correctly anymore with the A3640 installed.
To overcome this problem for the A3000T-040, Commodore designed new
revisions of these chips: RAMSEY-07 and DMAC-04. If your DMAC-02 has
problems with the A3640, all you would need to do is to exchange your
old RAMSEY and DMAC revisions with the newer ones. But in reality, you
can not buy a DMAC-04. In general, they are no longer available anymore
(except some single pieces that dealers might have in stock).
The RAMSEY-07 is available as a spare part (because it is also used in
the A4000T), but this will not help you. The problem is in the DMAC,
not in the RAMSEY and a RAMSEY-07 together with a DMAC-02 does not work
at all. You need either both chips in the old revisions, or both in the
new revisions. If you have an extremely old A3000, you might even have
a DMAC-01. This one runs very hot and has even more problems with '040
boards. I also heard of a RAMSEY-03, but don't know any difference to
So, if you have a DMAC that does not work with the A3640, you are
basically out of luck. What you could do in this case:
Buy another DMAC-02 (still available) and hope that one works with the
A3640 by chance. Replace the onboard SCSI host adapter by one on a
Zorro II or Zorro III plug in card. Forget about the A3640 and either
don't use an '040 board, or use one with a SCSI host adapter of its
Revision 11 BUSTER implements Zorro-III DMA, so you can use the
Fastlane Z3 or A4091 boards, which is not possible with older BUSTERs.
The rev. 11 BUSTER is also
faster than previous versions and more compatible with different plug
in cards.

IF you read that all the way thru, save your money. A DMAC04 and
Ramsey07 will not cure your problem with the card, as the file suggests
a SCSI Zorro card. Some would say I answered you questions the long way
around, but my resource of technical info is usually darn excellent.