Service manual

Standard colour test
The screen test displays four colour bars red, green,
blue and grey scale. Each colour bar is divided into 6
sections. The number at the top of the screen is the
value sent to the individual colour gun. Only one gun is
driven at a time for the red, green, and blue bars. The
grey scale bar is produced by equal amounts driving
each of the colour guns.
Starting from the left, the first block is no units of colour,
the next block contains a small amount of red (1 unit bit
0 set) the next more red (2 units - bit 1 set) continuing
along until the block is a full red (15 units of red - all bits
set).
The left most three blocks are out-lined with rectangles
of full colour. Check that the colour increases with each
block, to full intensity on the right most block. This
should be true for each colour bar.
The background is divided into two triangles; one brown
and one grey/blue colour. Check the linearity of the
dividing line and the colour of the triangles. A cursor is
made up of three squares and passes across the screen
from bottom left to top right. Also verify that the cursor
contains three rectangular outlines in colours green, blue
and red. Check the linearity of movement and also check
the transparency of the cursor as it moves across the
screen. Make sure that the colours do not change as the
cursor moves across the screen. Verify the border
colour.
Press F5 if the display is correct, or press F8 if not.
If the test fails, refer to the following section entitled
Action if video tests fail.
High resolution monochrome display
This test is not done.
Press the space bar to continue.
Standard VGA display
The same display is used in a VGA mode as in the
standard colour test. Repeat all the checks that were
performed on the standard monitor test on the standard
VGA display.
Note that the border is removed in the standard VGA
tests.
Press F5 if the display is correct, or press F8 if not. If the
test fails, refer to the following section entitled Action if
video tests fail.
Super VGA display
You are presented with a screen display that contains 16
squares, made from shades of red, green, blue and
grey. Check that the image is sharp, clear and stable on
the screen.
Note that the border is removed in Super VGA tests.
Press F5 if the display is correct, or press F8 if not. If the
test fails, refer to the following section entitled Action if
video tests fail.
Action if video tests fail
If there is no display check that there is power on the
monitor (green LED on) and that the brightness and
contrast controls are sufficiently advanced. If a video
cable adaptor is in use then make sure this corresponds
to one of the types described in Appendix E - Monitor
adaptor cables.
Check that the video loopback is functioning correctly by
making sure that it works on a known working machine.
Switch the machine off, hold down the key marked "." on
the numeric keypad and switch the machine on holding
down this key for at least a further 10 seconds. This has
the effect of resetting the monitor configuration to match
the type of monitor connected. If this fails to solve the
problem then substitute a known good monitor and
cable and try again.
If this action still fails to produce a display, remove the
top cover of the computer (see Part 2 - Disassembly
and assembly) and check on the main PCB that the
shunts on LK6 pins 1 and 2 and LK6 pins 3 and 4 have
not been dislodged. As a final action, remove the main
PCB and return it to an Acorn Authorised CSW for
repair.
If the display is corrupted, check the adaptor cable (if
used) against those listed in Appendix E - Monitor
adaptor cables and reset the monitor configuration via
the power up "." process. Check the monitor and cable
by substituting with known working items and repeat the
power up "." process. If the fault proves to be with the
main computer then you must return the main PCB to
an Acorn Authorised CSW for repair.
Video configuration test
A pass/fail message is displayed after testing the video
configuration circuitry.
This test will write data to the video loopback box via the
printer port which will simulate different monitor types at
the video socket. The monitor configuration is then
checked.
Action if video configuration test fails
If the test fails, check that the correct data is being sent
from the printer port by connecting the printer.
If the printer functions correctly, check that the monitor
loopback box is working by replacing the box and
cables.
If the video configuration test still fails with a known
working printer port and monitor loopback box, return
the main PCB to an Acorn Authorised CSW for repair.
Summary screen
At the end of the screen tests a final summary screen
will be displayed.
Press the space bar to continue.
Part 1- Fault diagnosis and repair Issue 1, November 1991 1-13