http://www.ant.co.uk/com/atomwide/Head1.html (The Risc Disc Volume 2, ~04/1995)

Fitting RISC OS 3 to a 300/old 400 series Archimedes

Stage One - Disassembling the computer

- Double-check that you have switched off the computer and disconnected it from the mains supply.

- Unplug the keyboard, mouse and all cables from the rear of the computer. Place the monitor, keyboard and mouse safely out of the way.

- Using a Philips-head (+) screwdriver remove the three screws along the top rear of the computer case and the one either side towards the front of the case. Put the five screws safely out of the way. Slide off the top cover of the case towards the rear. Lift it gently and put it to one side.

- Remove any expansion cards (”Podules•) from the computer by following the instructions supplied with them.

- Remove the screws retaining the backplane (if fitted) at each end of its metal support bar. Unplug the three power connectors and lift the backplane upwards to detach it from the main circuit board. Put the two screws safely out of the way.

Stage 2 - Modifying the main PCB & changing OS ROMs

- Locate the OS ROMS on the main circuit board and remove them from their sockets. Plug the carrier board into the four sockets so that the flying leads on it are positioned at the top left with the computer facing away from you (see figure 1).

figure 1

- Next, locate IC28 on the main circuit board and solder the three flying leads from the RISC OS carrier board to it. Make sure that the red lead is joined to pin 18, the green lead is joined to pin 17 and the blue lead is joined to pin 16 of the chip (see figure 2).

figure 2

Link settings

- The carrier board has a number of links labelled LK1, LK2 and JP7. The jumpers must be placed on the links as shown in figure 3.

figure 3

Stage Three - Completion of Installation

- Plug the RAM board back into the main board.

- Insert the RISC OS 3 ROMs into the sockets on the RAM card so that the notch in each chip points towards the back of the machine (see figure 5).

- Re-connect the three power connectors with long leads to the backplane (if fitted) (Yellow/+12V, Black/0V, Red/+5V). Refit backplane.

- Re-fit any podules you may have removed

- Replace lid on machine and secure with screws

Stage Four - Testing

To test that the RISC OS 3 ROMs are functioning correctly, power up the computer whilst holding down Delete on the keyboard, and then follow the test procedure outlined in the 'RISC OS 3 software upgrade fitting instructions' supplied with the upgrade kit.

RISC OS 3 includes all the modules necessary to control 8Mb RAM and ARM3 upgrades. These can both be removed from your hard (or boot) disc.

IMPORTANT

This upgrade requires modification to the computer's main circuit board and involves cutting and soldering. If you are at all unsure of doing this yourself, please contact Atomwide immediately for advice.

RISC OS 3 can be fitted by Atomwide to any machine. A charge of £20 will be made for carriage and £15 for fitting. Fitting is included for free if the RISC OS 3 ROMS are purchased from Atomwide.