maintenance
TROUBLESHOOTING
AND
REPAIR
signal deviates
from
this description, refer to
Section
3,
Theory of Operation,
in this
manual to
assist
you in troubleshooting
the
clock
oscillator circuit.
4D-29.
Power
Reaet
Connect an
oscilloscope probe to the
RESET
input (pin
22)
of Ul, The
signal should
generate a low
to high transition on
power-up and remain high during
normal
operation.
Turning the
power
on and off generates
active low reset pulses to U 1 , If a
problem with
the reset circuit
is
suspected, refer to
Section
3,
Theory of Operation, and
troubleshoot
the reset
circuitry.
4D-30.
Microprocessor
Inputs
Input pins
to
Ul,
CRUIN (pin
13)
,
INTI (pin
15),
HOLD (pin
18),
NMl
(pin
21),
and
READY (pin
23),
should all be high. If any of
these signals
are not high,
correct
the fault
before continuing on.
4D-31. IEEE-488
Interrupt
Verify
that the IEEE-488
Interface
interrupt signal, lEINTL, is in the
inactive
(high)
state.
If lEINTL is active,
either
troubleshoot the interface to the IEEE-488
Interface
option, or temporarily bend
out
pin 14 of Ul and tie it to +5V.
After
completing the above
steps, there should be activity on the
address,
data, and
control
lines
as
the
microprocessor executes instructions.
4D-32- Microprocessor Bus
The dynamic nature of
microprocessor bus circuitry makes it very
difficult to verify the
data
transmitted at any
given time. However, most common bus faults
show recognizable
symptoms. Look at each of
the data
(DO
to D7), address (AO to A
15),
and bus
control
(CLKOUT, DBINL, WEL,
MEML) signals with an oscilloscope.
Suspect
inactive signals or signals that
enter invalid
logic states. Also
compare
the driver
inputs and outputs of
buffered signals. A combination of
observation and
experience
is
helpful
here. An ohmmeier or a
pulse
generator may be useful in
further
investigating
suspected
signals.
4D-33. Address Decoder
Several
levels
of address
decoding
are used to select all the memory
and I/O
devices.
The
inputs to the
address decoders come
from
the buses and present
challenges
similar to
troubleshooting
the buses. A suggested
approach
is to first choose a
decoding path
to a
particular
device or group of
devices.
Start at the highest level of
decoding,
and one at a
time verify that each part
in the path is good.
4D-34. Display and
Controls
If the
display
shows signs of
activity,
but has missing or bright digits
or segments, the
problem
is
most likely in U 18 on the A2A7
Controller or on one of the
data latches or
drivers
on
the AlAl Display
PCB. If
the display is blank and
the
Controller is
operational,
check the various
power
supplies and the display blanking
circuitry on
the
Display
PCB.
Two special
function-service
tests are available to test the
front
panel indicators
and keys.
[SPCL]
[0][3]
keys check the front
panel
displays
by
lighting all
segments.
This test is
aborted by
pressing any key on the
Generator.
The
[SPCL]
[0][4]
keys
allow all normally open keys to be
checked. As each
key is
pressed,
its row and column address
is
displayed in the center of
the
FREQUENCY
display field.
See
Table 4D-9 for the address
codes
for each key. This test
is
exited by a
clear
entry.
4D-11
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