A3640 Reference

The A3640 is the stock 68040 processor board that comes with most A4000s. It contains a 25 MHz 68040; some boards came with the 68LC040, which is a 68040 with no built-in math coprocessor functions. The A4000 User's Guide has instructions on upgrading from a 68EC040, which has no math coprocessor or memory management unit (if any A4000s were ever shipped with 68EC040 processors, there were very few of them). Revision 3.1 or 3.2 boards with U209 marked as "-02" or "-03" can be used in A3000 or A3000 tower computers. (For more information on A3640 board revisions and bugs, see Internals/Definitive Buster.)

To install an A3640 into an A4000/030, jumper J188 under the processor board must be switched from INT to EXT.

The "cut and jumper" patch mentioned by Dave Haynie in the Definitive Buster section is: lift pin 6 of U200, and short pads 6 and 7 on U200 (for more details, see below). This, in combination with an upgrade to the U209 PAL, converts a 3.0 board to 3.1. The only difference between 3.1 and 3.2 boards is another upgrade to the same PAL. The 3.0 revision of the A3640 has enough problems and incompatibilities (reported not to work at all with A4000/030 rev D, for instance) that it's worth doing the cut and jumper patch even without the PAL upgrade.

Information on PAL upgrades can be found at: ftp://iaehv.nl/pub/users/paul/amiga/A4KPALS.LHA

(See also Tips/Processor Board Mounting.)


J100: Enable *CacheDisable *MMU Disable

  1-2 Closed and 3-4 Closed: Enable CDIS* MDIS* (caches and MMU disabled
                             at powerup and reset: default).

J400: Enable MAPROM: Enable remapping circuit for loading Kickstart into Fast RAM with a developer utility program.

  1-2 Closed: MAPROM enabled (default).
  3-4 Closed: MAPROM disabled.

Cut and Jumper Patch For A3640 Revision 3.0 by Marcel DeVoe

Replacing or re-programming the PAL U209 to version -02 is often not necessary for operation as this is found to be enough to stop system crashes with some fast Zorro III boards such as graphics cards.

If you are going to do it yourself but are not too sure of your ability with a fine soldering tool, then someone else who does might do the job for you. One fellow said it only cost him a couple of US dollars and about 5 minutes to have someone in an electronics repair shop do the job. You will need a thin soldering iron with a needle-like tip for getting into small places and some very thin solder.

The IC is numbered U200 and should be marked as such near it on the board. It is a smaller IC with 8 or 10 pins or so running along just 2 sides, the top and bottom of it for a total of 16 or 20 pins. When you hold the IC so you can read the numbers on it, the lower left hand corner has a small dot on it either as printed with ink or an indentation into the plastic or one corner could be bevelled depending on the manufacturer.

This is pin "one". The pins are counted counter-clockwise from it all around the IC, as an IC is normally read upside down. But you are only concerned with the same side as pin one.

  |<-about 1.5?cm->| (a bit less than an English inch ;)

   1 1 1 1 1 1 1
   6 5 4 3 2 1 0 9
   | | | | | | | |
 |                 |
 |   xxxxxx xxx    | U200
 |                 |
 |   xxxx  xxxx    |
 |                 |
 |o <-dot          |
   | | | | | x | |
   | | | | | |=| |
   1 2 3 4 5 6 7 8

Unsolder pin 6 from the circuit pad and bend it up and out of the way. Then short the trace pad that pin 6 was on underneath to pin 7 with some solder or a small piece of wire. Some people cut pin 6 right off after unsoldering it to make sure it doesn't bend over and short to something else. But I wouldn't recommend doing that right away in case you should make a mistake and only then until you are sure everything is running properly.