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Model 8901B
Service
8-9. POWER-UP CHECKS
When the Modulation Analyzer is first turned on (or if 40.0 SPCL is entered), the instrument goes
through a series of operational checks. If a check fails, an error code is displayed for two seconds on
the four internal TEST LEDs on the A13 Controller Assembly. The sequence then continues on to the
next check.
Except for the check of the front-panel LED annunciators, no indication of the power-up sequence or
its results is given on the front-panel display. The principal advantage to using the Power-Up Checks
is that the keyboard and display need not be operational.
To use the Power-Up Checks, remove the top cover, remove any jumpers that may be on the four TEST
test points
(A,
B, C, and D) on the A13 Controller Assembly, remove any signal at the INPUT and
switch POWER to STBY for five seconds (to discharge the supplies) and back to ON. Observe the four
TEST
LEDs on the top of the Controller Assembly as the instrument powers up. The LEDs should
light in the following sequence:
1. Indeterminate for about
second.
2.
( )( )(
)(1) for about 2 seconds.
3.
( )(
)(2)(
)
for about
1 / 4
second.
4.
(
)(4)( )( )
for about
second.
5.
(8)(4)(2)(1) for about 10 seconds.
6.
( )( )(
)(1), with (1) blinking indefinitely until a key is pressed.
The Power-Up Checks proper begin at step
2
and are carried out in the following order:
1. Front-Panel Annunciator Check.
All front-panel LEDs and display segments and decimal points
are lighted and remain so throughout the tests that follow and for a few seconds afterwards. Failure
of one or more LEDs or display segments to light indicates that the respective components or
drive circuits have failed. See Service Sheets 26 and 27.
2. Read Only Memory Check. The checksum of each of the read only memories
(ROMs) is read
and compared against a stored reference (stored in ROM
1).
This
is
similar to issuing a series of
52.N SPCL commands (see Service Special finctions, paragraph 8-7). When a wrong checksum
is found, the four TEST LEDs blink for one second with the binary code of the ROM number.
For example, if ROM 3 is faulty, the
TEST
LEDs will blink
( )(
)(2)(1) (that is, a binary 3). The
check then continues on to the next ROM. See Service Sheets BD5 and 24. If no faulty ROM is
found, a steady
( )( )(
)(1) appears for about 2 seconds.
3.
Random Access Memory Check.
Data is written into and retrieved from the random access
memory (RAM). During the test,
( )(
)(2)( )
is output to the
TEST
LEDs for about 2 seconds. If
the data read back differs from the data entered, the failure is indicated by outputting the same
code for an additional 2 seconds. See Service Sheet 24.
4. Instrument Bus Parity Check. A parity check of the data lines of the Instrument Bus is made.
A
failure is indicated by
( )(
)(2)(1) on the TEST LEDs for about 2 seconds. See Service Sheets
BD5, 15, and 24.
5. Local Oscillator Check.
The Local Oscillator (LO) is given a series of tests similar to issuing the
54.0 SPCL command (see Service Special Rmctions, paragraph 8-7). During the test,
(
)(4)(
)( )
is output to the TEST LEDs for about second. A failure is indicated by outputting the same
code for an additional 2 seconds. See Service Sheet BD2.
6.
Keyboard Check.
The keyboard is scanned to see
if
any keys are down. If a key
is
down, error
code
(
) ( 4 ) (
)(1)
is output to the TEST LEDs for 2 seconds. See Service Sheets BD5 and 25.
Power-Up Checks
8B-17
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