A3 Assembly’s Control Circuits
A digital control problem will cause the following three steps to fail.
1. On the HP
8560A, press
(-1,
ATTEN
MAN,
0,
a,
and
(dB.
2. A click should be heard after pressing dB in step 1, unless
ATTEN
was previously set to
70
dB.
3. Press
0,
@,
and
@.
Another click should be heard. If no clicks were heard, but the
ATTEN
value displayed on the CRT changed, the digital control signals are not operating
properly.
Analog Bus Drivers
See
function block N of A3 Interface Assembly Schematic Diagram (sheet 4 of 6).
1.
Press
cm)
on the HP 8560A, and set the controls as follows:
SPAN
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 Hz
TRIGGER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Single
2.
Monitor
A3U401
pin 3 (LRF_STB) withan oscilloscope or logic probe. This is the strobe
for the Al5 RF assembly.
3.
Press
(mCTRL)
INTERNAL MIXER and check that pulses occur when toggling between
SIG ID ON and SIG ID OFF.
4.
Monitor
U401
pin 5 (LFC_STB) with
an oscilloscope or logic probe. This is the strobe for
the Al4 Frequency Control assembly.
5.
Press
(AMPLITUDE)
and check that pulses occur when toggling between
ATTEN
settings of
10 and 20 dB.
6.
Monitor
U401
pin 7 (LIF_STB) with an oscilloscope or logic probe. This is the strobe for
the A5 IF assembly.
7.
Press
(AMPLITUDE)
and check that pulses occur when toggling between REF LVL settings of
-10
dBm
and -20
dBm.
8.
9.
10.
11.
12.
13.
Monitor
U401
pin 9 (LLOG_STB) with
an oscilloscope or logic probe. This is the strobe
for the A4 Log Amplifier/Cal Oscillator assembly.
Press
(-1
and check that pulses occur when toggling between LINEAR and
LOG dB/DIV .
To check the Address and Data Lines, place a jumper from
A3TPl
and
A3TP2
to
A3U406
pin 20
(+5
V).
Check that address lines
A0
through A7 and data lines DO through D7 are all TTL high.
If any address or data line is low, set the LINE switch off and disconnect the W2 control
cable from A3J2. Set the LINE switch on. Ignore any error messages.
Check that address lines
A0
through A7 and data lines DO through D7 are all high. If
all address and data lines are high, suspect a fault either in W2 or one of the other four
assemblies which connect to W2.
7-26
ADC/lnterface
Section
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