A59 Digital Interface Assembly-Level Troubleshooting; Diagnostics; Change Detectors; Service Request - HP 8340B Manual

ASS Digital
Interface
Assembly-Level Troubleshooting
DIAGNOSTICS
The A60 processor
responds
to inputs from the A5Q assembly using the
processor service request
and change detector circuitry for the following conditions:
• oven or unlock changes
•
overmod or unleveled condition changes
• external reference switch changes
• sweep
events from the A57 marker/bandcross assembly
CHANGE DETECTORS
Verify the Change Detector Circuitry
1.
Connect
a
logic probe or storage oscilloscope to
A59TP8.
2.
Change the rear panel frequency standard INT/EXT switch and verify that this generates an
active
low pulse.
Verify that the front
panel
EXT REF LED lights
when the switch is in
the EXT position.
3.
Press
[CW]
and disconnect
one of the snap-on cables in
the phase lock loop (e.g. A39W1 at
A40J3). Verify that the front panel UNLOCK indicator on the front panel lights.
Verify
a
pulse at TP8.
4.
To check HOVC, disconnect the instrument from line
power
for five minutes, then quickly recon¬
nect line
power
and turn the
power
switch on. Verify that the
OVEN
light goes on for
a
few
minutes, and then goes
off.
SERVICE REQUEST
Verify the Processor Service Request
1.
Press [INSTR PRESET] [CW] and verify that the RUN light on the
A60 processor assembly
is off.
If
not, the
LSRQ
line
is pulled down, and the
reset
circuitry
is
faulty.
HP
8340B/41B
A59 Digital
Interface Assembly-Level Troubleshooting F-ll