HP 7942 Service Manual page 75

Service Information
7942 and 7946
time by controls on the rear panel of the disc drive
or by the host computer using the Initiate
Diagnostic command. Details of the diagnostic
tests are provided in the following paragraphs.
4-21. SELF-TEST SUBTESTS
The subtests run during self test can be divided
into six functional groups. A general description of
the tests in each group, listed in the order that they
are performed, is provided in the following
paragraphs. Refer to tables 4-1 and 4- 2 for a
listing of the subtests and the failure conditions
detected by the tests.
The first group of subtests (01 through 07, table
4-1) checks the operation of the HDC. The
subtests include a short checkout of the HDC
microprocessor, a checksum of both the EXEC
EPROM and the DDC EPROM, exhaustive
write/read test of all of the RAM, a loopback test
of the DMA gate array IC, a verification of the
timer circuitry, and a test of the HP- IB interface
IC. A full set of these sub tests is run only when self
test is initiated at power-on. When self test is
initiated by either the SELF TEST switch or the
host, then only the timer test, the DMA test, and a
limited RAM test are performed. This is to protect
the existing run -time environment. The subtests
described above check the operation of the IC's,
circuits, and interfaces resident in the HDC.
The second group of subtests (OAH through 12H,
table 4- 2) checks the operation of disc drive
functions independent of disc drive assembly AI.
These subtests include tests of the DDC resident
IC's and circuits, a checksum of the device specific
PROM, and the sensing of the proper 12 volt
power.
The third group of subtests (13H through 1 CH,
table 4- 2) checks the operation of disc drive
assembly A 1 to the extent of servo activity. The
disc drive is selected, a restore command is
performed and a few seek commands are issued
and monitored for proper completion, direction,
and pulse count.
The fourth group of subtests (lDH through 2SH,
table 4- 2) performs further checks of the disc
drive assembly A 1 servo mechanism, and the read
function, as far as position sensing. A scan ID
command verifies that the sector headers can be
4-6
read. A more exhaustive sequence of seeks is then
executed, both verifying the subsequent location as
well as monitoring the speed performance.
The fifth group of subtests (26H through SEH,
table 4- 2) checks seek, read, and write, both one
and two sectors, at the inner diameter (ID) and the
outer diameter (OD). Reads and writes are also
performed on every surface.
The sixth group of tests (SFH through 6SH, table
4- 2) checks out the error and fault detection
circuitry. Circuit tests include: ID not found on a
scan ID command, underrun condition, a command
aborted, and both ECC correctable and
un correctable errors.
Note: An additional test is run after a
successful initialize and read
(subtest 26). This test uses subtests
66H through 6 SH. The test
attempts to read the
factory-recorded product number
from the disc and match it with the
product number resident in the
HDA description PROM located in
the DDC.
4-22. SELF-TEST ERROR REPORTING
There are three ways which the disc drive reports
self -test results to the user. The first way is by
means of the front panel FAULT/ON LINE
indicator. The second way is via the self -test
display on the rear panel. The third way is by
means of the CS/80 Request Status command. The
following paragraphs provide details of how these
three methods are used to report self -test results.
4-23. FAULT/ON LINE INDICATOR. The red
and green LED's which comprise the front panel
FAULT/ON LINE indicator signal the operating
status of the disc drive. See figure 4-1. A
momentary solid red and green display and then a
flashing green display occurs when the disc drive is
powered on and self test is executing.
If the
display remains a solid red and green, this means
that the host dependent controller (unit 2) has
f ailed self test. At the end of self test, a solid green
display indicates that the disc drive has passed self
test and is ready for operation. A solid red display
indica tes tha t the disc drive has failed self test.
When a self -test failure is indica ted, the 2 -digi t