Oliver Knorr, 24-Jan-1995 


Using the A3640 in an A3000

The A3640 is Commodore's 25MHz 68040 board used in the A3000T-040, A4000/040 and
A4000T. Originally it was designed to fit in the desktop A3000, too (hence the name).
Unfortunately, this did not work as good as expected. Several problems were found, so
Commodore never recommended the A3000 installation of the A3640 officially.

Because used A3640s are often available at a good price from people who upgraded 
their
A4000/040 with a faster CPU board, one might be tempted to use it in the A3000 in 
spite of the
known problems. With a little work and a little luck, it might work very well.

For daring people who want to do such an upgrade of their A3000, I collected the 
following
information about possible problems and how to solve them. Good Luck!

A3640 board revisions

You can find three revisions of the A3640 in circulation: 

3.0 
       This one will not work at all in the A3000 (though it might work in the 
A4000!). You
       need to give such a board to a repair center for an upgrade to 3.1 or 3.2. 
3.1 
       This one can work fine in the A3000, but has a bug that prevents certain 
Zorro-II DMA
       cards like the GVP PhonePak from working. In most cases, this revision (which 
is the
       most common one) is OK. 
3.2 
       Like a 3.1 board, with the above mentioned bug fixed. 

When checking the A3640 revision number, also have a look at the PAL or GAL chip at 
position
U209. Its revision number should match that of the A3640 in the following way: 

A3640    U209
  3.0     -01
  3.1     -02
  3.2     -03

Mechanical problems

Though the size of the A3640 board fits perfectly even in the small A3000 desktop 
case, you can
have some problem with the height.

The earlier A3640s have a large heat sink on the 68040 CPU that would need some room 
in one
of the two floppy drive bays of the A3000. Newer A3640s come with a flat heat sink 
that fits
under the drive bridge without problems.

If the heat sink of your A3640 is too high, probably the best thing to do is to get a 
smaller one
(you could also get a larger case or modify the drive bridge). Largely available are 
i486 CPU
coolers that consist of a heat sink with a small fan and mounting clips.

Because the i486 is a little bit smaller than the 68040, you should get a i486 cooler 
with
elastic clips that can be widened a bit. You also need a cooler where the little fan 
can be removed,
to make it fit below the drive bridge.

Heat

One of the reasons why Commodore never recommended the A3640 for the A3000 is heat. 
The
A3000 was designed to be upgradable with such a board, but the 68040 turned out to 
run hotter
than expected and hotter than the A3000 was designed for.

If you use the A3640 in the A3000 desktop, you always risk overheating the 68040 or 
any
other part in the computer. This could cause errors, crashes or shortended life of 
certain parts.

To avoid heat problems, it might be a good idea to install an additional fan in the 
A3000, avoid
using hot hard drives inside the case and not using it with high room temperatures.

Operating sytem ROMs

There are two socketed ROM chips on the A3000 mainboard that contain the ROM part of 
the
Amiga's operating system. There are three different pairs of ROMs available for the 
A3000: 

V36 boot ROMs 
       The older A3000s have these ROMs. They are only used to load an image file of 
a newer
       ROM version from hard disk (or floppy disk) into RAM. These V36 ROMS are not
       compatible with 68040 processors, so your A3640 will not work at all with such
       ROMs. You need to get the A3000 version of the AmigaOS 3.1 upgrade kit and 
install the
       new ROM chips that come with it. 
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,
       execept 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. 
AmigaOS 3.1 ROMs 
       This is the newest ROM version available for the A3000, and the best one to 
use with the
       A3640. No A3000s were ever sold by Commodore with these ROMs, but they are
       available in an upgrade package that also contains a new set of Workbench 
disks and new
       manuals. If your A3000 still has an older ROM version, it would be a very good 
idea to
       upgrade to 3.1, regardless if you have problems or not. Some new software 
requires 3.1
       and it is also much nicer to work with because of its new features and fixed 
bugs. 

If you have a very old A3000 mainboard revision, the ROMs might sit in a special 
adapter
socket, called ROM tower. When upgrading to 3.1, you should exchange the ROMs, but 
continue
using the sockets. I heard of some cases, where A3000s with ROM towers refused to 
work with
3.1 ROMs. In this case, you should probably contact the manufactuerer of the upgrade 
kit for a
different set of ROMs.

When upgrading to newer ROMs, remember the orientation and the numbers of the old 
ROMs you
remove! Insert the new ROMs in the same direction and with the same number in the 
same
socket. Do not pay attention to the numbers printed on the motherboard, they might be 
just the
wrong way around. If you confused the two sockets, your A3000 will refuse to boot, 
but nothing
will be damaged. But do not confuse the orientation of the ROMs, I'm not sure if it's 
harmless to
put them in the wrong way. For the orientation, pay attention to the mark in the chip 
case itself,
not to the orientation of the printed text on the chips!

A3000 mainboard jumper positions

These are the correct jumper positions to use the A3640 in an A3000 desktop: 

J100: 3-4
J102: 2-3
J103: 1-2
J104: 2-3

The '1'-Position is where the printed arrow head is.

Do not change any jumper on the A3640 board itself!

RAMSEY and DMAC

The RAMSEY and DMAC chips are important A3000 custom chips that, among other things,
implement a 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. They are no longer available anymore.

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 board. I also heard of a RAMSEY-03, but don't 
know any
difference to RAMSEY-04.

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 own. 

BUSTER

The BUSTER chip (or more exactly Super-Buster, as the original Buster is a different 
chip used
in the newer A2000s) is important for the Zorro-III slots in your A3000. There are 
many
different revisions of it, but any of them should work with the A3640. Your A3000 (if 
not
upgraded) probably has a BUSTER revsion 05, 06 or 07.

Having said that, you might still want to upgrade your BUSTER to a revision 11 part 
when you
install the A3640. This is no must, but a good idea. The revision 11 BUSTER 
implements
Zorro-III DMA, so you can use cards like the Fastlane Z3, which is not possible with 
older
BUSTERs. The rev. 11 BUSTER is also faster that previous versions and more compatible 
with
different plug in cards.

There is a BUSTER rev. 09 available, too. Do not buy this one, it also tries to 
implement
Zorro-III DMA but has a bug in this. The rev. 11 part also is the only one, which has 
an extra
hack to fix a bug in a different A3000 chip.