Analog Bus Timing - HP 8560A Service Manual

14. If any address or data line is low, check the appropriate input of either U405 (data lines)
or U406 (address lines).
15. If a data line input is stuck low, check the data bus buffer. If an address line input is
stuck low, check A3Wl and the A2 Controller assembly.
16. If the appropriate input is high or toggling between high and low, suspect a failure in
either U405 (data lines) or U406 (address lines).
17. Remove jumpers.

Analog Bus Timing

See function block P of A3 Interface Assembly Schematic Diagram (sheet 4 of 6).
Analog bus timing (ABT) generates the strobes for the A4, A5, A14, and Al5 assemblies.
The Al4 Frequency Control assembly also requires a qualifier for its strobe, LVFC-ENABLE.
enable line to demultiplexer A3U407 goes low.
1. Press (PRESET) on the HP 8560A and set the controls as follows:
C E N T E R F R E Q
SPAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..lOO MHz
2. Check that A3U407 pin 1 goes low approximately 2 ps after HANA-BUS (A3U400 pin 3)
goes high.
3. If HANA-BUS is absent, check for pulses on ABT A3U505 pin 2 and IA10 (A3U505 pin
4. If A3U407 pin 1 is not delayed 2 11s from HANA_BUS, check for the presence of the
1 MHz HBADC-CLKO.
5. If A3U407 pin 1 is not delayed 2 ps from HANA_BUS and HBADC_CLKO is correct,
suspect a fault in either A3U414 or A3U400.
6. Press c-1 and set the controls as follows:
SPAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OHz
TRIGGER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..SINGLE
7. Monitor A3U401 pin 3 (LR-STB) with an oscilloscope or logic probe. This is the strobe
for the Al5 RF assembly.
8. Press (mCTRL) INTERNAL MIXER
SIG ID ON SIG ID OFF.
and
9. Monitor A3U401 pin 5 (LFSTB) with an oscilloscope or logic probe. This is the strobe
for the Al4 Frequency Control assembly.
10. Press (-1 and check that pulses occur when toggling between
10 and 20 dB.
11. Monitor A3U401 pin 7 (LI_STB) with an oscilloscope or logic probe. This is the strobe
for the A5 IF assembly.
-10 dBm and -20 dBm.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...300 MHz
and check that pulses occur when toggling between
settings of
REF LVL
settings of