Note: This document was provided by Oliver Knorr and is being mirrored on National Amiga.

Oliver Knorr, 1997-12-28

Using the A3640 in an A3000

The A3640 is Commodore's 25 MHz 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:

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.
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.
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 computer 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.

If you want to buy an A3640 with the high heat sink and need to replace it by a smaller one, you should check how the old heat sink is mounted. Normally, it should be only fixed with a metal clip that can be opened to remove the heat sink, but I also heard of one case, where the heat sink was glued to the 68040 CPU and thus virtually impossible to remove.


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 as an upgrade. You can either get only the ROMs, or a complete AmigaOS 3.1 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. As some new software requires AmigaOS 3.1 and it is also much nicer to work with because of its new features and fixed bugs, I would recommend to get the full upgrade package.

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 certain 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 (QUADCLK): 3-4 (EXT)
J102 (BRDCLK) : 2-3 (INT)
J103 (FPU)    : 1-2
J104 (CPUCLK) : 2-3 (EXT)

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

For the 16 MHz A3000, some additional jumpers need to be changed to switch the board to 25 MHz operation (information submitted by Christian Just,

J151 (ROM SPEED): 1-2 (25M)
J152 (ROM SPEED): 1-2 (25M)
J851 (CPU SPEED): 2-3 (25M)

Do not change any jumper on the A3640 board itself!

In case want to remove your A3640: the jumper settings for the various A3000 desktop models without CPU board can be found in your A3000 manual, on the first page of Appendix E.


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 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:


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 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.

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.


The A3000 has a small amount of nonvolatile RAM, that is used to store the settings for the onboard SCSI host adapter. Christian Just ( reported, that he heard of several cases where the contents of this RAM were lost when an A3640 was installed. This resulted in SCSI problems, that vanished when the settings were restored with the SetBatt utility. It is available as util/wb/SetBatt-1.2.lha on Aminet.

As I can not confirm this and have no exact knowledge what is happening here, I would appreciate any further information about this battmem problem.