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Service
Model 8901B
TROUBLESHOOTING
General
The troubleshooting checks that follow are a starting place for locating an instrument fault. They are
easy to perform and give much key information in a short amount of time. In most instances they can
differentiate between an instrument hardware failure and a Controller
or
software problem. The checks
should be done in order.
( J 1 ) LineCheck
Procedure: Remove instrument top cover (three screws) and switch POWER to ON.
Normal Indication:
1. The fan runs indicating power is present on the power transformer secondaries.
2. The five green LEDs on the A10 Power Supply Regulators Assembly are lighted indicating
that the supplies are nominally operating.
I f Indication Abnormal:
1. Check the rear-panel line fuse and line voltage selector. Check Mains wiring. (See Service
2. Check the individual regulators. (See Service Sheet BD5.)
Sheet 31.)
@ Power-Up Checks
Procedure: If there are any jumpers on the TEST test points on the
A13 Controller Assembly,
remove them. Switch POWER to STBY for five seconds and back to ON. Note the sequencing
of the four
TEST LEDs on the top of the Controller Assembly as the instrument powers up.
Normal Indication: The four TEST LEDs light in the following sequence:
1.
Indeterminate for about
second.
2. (
) ( ) ( )
(1) for about 2 seconds. This indicates the start of the power-up routines and the
3.
( ) ( )
(2)
( )
for about
1/4
second. This indicates the
start
of the power-up routines and the
4.
( )
(4)
( ) ( )
for about
1/4
second. This indicates the running of the Local Oscillator Check.
5. (8) (4) (2)
(1)
for about
10 seconds. This indicates that all power-up checks passed
and that
6.
( ) ( ) ( ) (l),
with (1) blinking indefinitely until a key
is
pressed. The behavior of the LED
Any other sequence indicates a failure of the check. Passing this check indicates that the Controller
is functioning properly and that there is no catastrophic failure in the following circuits:
run of the Read Only Memory Check.
run of the Random Access Memory Check.
a visual front-panel check can be made. (See
(J3)
below.)
(1) is
also affected by the presence of an input signal.
Read Only Memory,
Random Access Memory,
Instrument Bus,
Local Oscillator (tuning only),
Keyboard (only that no key is down).
I f Indication Abnormal: If the TEST LEDs come on and remain in the random state
of
step
1
above, unplug the A14 Remote Interface Assembly and try again. If still faulty, check the
Controller Kernel. (See Service Sheet BD5.)
If other indications appear in or after step
2 above, consult
Power-Up
Checks, paragraph 8-9,
which discusses the individual checks, documents the error indications, and cross references to
the service sheets.
8D-12
Service Sheet BDl
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