Service manual

Service Manual
The following is a normal POST sequence:
1 The screen colour is first set to purple to indicate
testing has started. The first part of the test:
• performs a brief ROM and RAM test
• initialises the 10 controller
• initialises the Video controller.
This part of the test lasts less than a second and is not
easily visible. However, certain system failures may
cause the machine to crash or halt during this phase:
no further activity will occur and this may be read as a
major failure, probably of the 10 system.
2 The screen colour changes to blue if the simple
memory test above is passed, indicating that a more
extensive test has started. This phase can take up to
12 seconds on a 16MB machine.
3 Tests are now performed on the video and sound
controller, VIDC. These are again very brief.
4 The screen colour reverts to purple and a test is
performed for an ARM 3 processor. This test relies on
good RAM, and will not be performed if a failure has
already been detected.
5 The screen now turns black, with a memory size
message displayed, indicating that the self-test is now
complete. The system will normally start RISC OS.
However, an unexpected failure could leave a purple
screen displayed, indicating a major system fault. If a
fault has been detected, RISC OS will not start
immediately. Instead, the entire screen will change to red,
and the LED on the disc drive will flash. The flashing
sequence indicates the fault detected in accordance with
the fault codes described in the section entitled Result
reporting on page 5-9 — an 8 digit hexadecimal number
is displayed as 8 groups of 4 flashes, where a long flash
indicates binary 1 and a short flash indicates binary 0.
Fig 5-1: The test link
Fig 5 - 2: Link positions on main PCB
5-2 Issue 2, June 1991 Part 5 - Main PCB fault diagnosis