Service manual

Chapter 4 Diagnostics
30
System (BIOS) ROM
Test
BIOS ROM chip calculates an eight-bit checksum. Test failure causes an
error code to be displayed and the boot process to abort.
Memory Subsystem
Test
Tests the physical configuration of the memory subsystem. The test checks
for valid memory module combinations. Test failure causes an error code to
be displayed.
RAM Refresh Timer
Test
Tests the RAM refresh timer circuitry. Test failure causes an error message
to be displayed and the boot process to abort.
Interrupt RAM Test
This test checks the first 64 K of system RAM used to store data
corresponding to various system interrupt vector addresses. Test failures
cause an error message to be displayed and the boot process to abort.
CMOS RAM Test
Checks the CMOS RAM for start-up power loss, and verifies CMOS RAM
checksum. Test failure causes error codes to be displayed.
Cache Memory Test
Tests the processor's internal cache RAM. Test failure causes an error
message to be displayed and the boot process to abort.
Keyboard/Mouse
Controller Test
Checks for proper operation of the Keyboard/Mouse Controller. Test failure
causes an error code to be displayed.
Timer 0/Timer 2
Test
Tests Timer 0 and Timer 2. Test failure causes an error code to be displayed.
DMA Sub-system
Test
Checks the DMA controller registers. Test failure causes an error code to be
displayed.
Interrupt Controller
Test
Tests the interrupt masks. Test failure at any point causes an error code to be
displayed.
RAM Address Line
Independence Test
Verifies the address independence of real-mode RAM (which verifies the
address lines are not stuck together). Test failure causes an error code to be
displayed.
Real-Mode Memory
Test (First 640 K)
Read/write test on system real-mode RAM. The test checks each block of
system RAM to determine how much is present and displays the current base
value upon successful completion of the test. Test failure of a 64 K block of
memory causes an error code to be displayed and skipping the remainder of
the memory test.
Shadow RAM Test
Tests Shadow RAM in 64-Kbyte segments, except for the segments
beginning at A000h, B000h, and F000h. If they are not being used, segments
C000h, D000h, and E000h are tested. Test failure causes an error code to
be displayed.