HP 5065A Operating And Service Manual page 327

Model 5065A
Circuit Diagrams, Theory, and Maintenance
Repairs
Before attempting repairs, perform the following proce­
dures:
NOTE
Some of the circuits on the CLOCK DISPLAY
assemblies are CMOS. Use high impedance
test equipment when checking signals. Pre­
cautions should be taken when removing or
replacing these circuits to prevent damage
from static charges.
a. Momentarily set front panel DIVIDER MODE switch to
START.
b. Check CIRCUIT CHECK meter in 1 MHz position for
reading of approximately 40. If reading not present, trou-
bleshoot A6 assembly.
c. Check front panel 1 PPS output. If not present, trou-
bleshoot A5 assembly.
d. If the display is not lit, press STANDBY DISPLAY
switch. If display lights and operates normally, the instru­
ment is not operating from AC power. This condition is
normal. If the display does not light when the STANDBY
DISPLAY switch is pressed, perform troubleshooting pro­
cedures described below.
e. Read A19A2 Clock Display Theory of Operation.
A19 Assembly Removal
Prior to removing or reinstalling the Clock Display, turn off
all operating power. Wire and cable length to the clock
panel or clock rear board is sufficient to permit removal of
the clock without disconnecting these wires or the cable.
Place the clock on a pad or cloth to minimize scratch
damage or shorting of circuit traces. Then, proceed as
follows:
a. Turn off all operating power.
b. Remove the instrument top cover. In Option 003
disable the internal standby battery.
c. Use a 5/16" spin-type wrench and remove three
5/16" nuts which secure the clock to the instrument
front panel. Retain the nuts for reinstallation.
d. Press at the bottom-rear then at the top-rear of the
clock until it is loose.
e. Carefully remove the clock. Gently pull the connected
wires and cable forward and set the clock on the work
surface.
f. With clock assembly removed, connect a jumper,
or clip lead between the clock chassis and the instrument
chassis.
g. Before applying operating power ensure that the
exposed LED Clock boards and wires are not in contact
with any metal objects or surfaces. Apply operating power.
h. To reinstall the Clock Display, turn off all oper­
ating power. In Option 003, disable the internal standby
battery.
i. Perform steps b to e in reverse order. (See Note.)
NOTE
While installing the clock into the instrument
front panel, check that wires are not pinched by
screws or metal work. Position the wires for a
neat appearance after installation.
j . When clock is reinstalled, apply power and set
time as described in paragraph 3-28 of the 5065A Oper­
ating and Service Manual.
Troubleshooting
General
Procedures in this section describe fault isolation to the
circuit board level, disassembly of the clock, and trouble­
shooting information for each of the three circuits.
Clock System Troubleshooting
To perform the following tests, remove the clock from the
instrument and connect as described in A16 ASSEMBLY
REMOVAL.
A19A1 Power Supply Check
NOTE
All voltages measured with respect to instru­
ment chassis.
a. Measure voltages indicated below. Be sure to clock
chassis is grounded to instrument chassis.
VOLTAGE
+ 26±4Vdc
+ 12 ±2Vdc
+ 5 ±.5Vdc
LOCATION
A19A1P1(3)
A19A1(R)
A19A1P1(4)
b. If the +26 or +12 volt supplies are out of tolerance,
troubleshoot the source of these voltages. If the + 5V supply
is out of tolerance, remove the A19A2 Assembly and meas­
ure the voltage again. If voltage now is correct, go to step
b i 2 i .
i11 If voltage remains out of tolerance, troubleshoot
A19A1, 5V regulator assembly.
121 If voltage is now correct it indicates a short or low
impedance on 5V line or defective current-limit circuit:
troubleshoot 5V line and circuits on A19A2 which use
5V. If these are OK, check current-limit circuit of A19A1.
NOTE
An external 5V can be used in place of A19A1 output.
c. Check for +1V, 150nsec, 1 PPS signal at A19A1.W..
Be sure Clock Display chassis is grounded to instrument
chassis. If pulse not present, troubleshoot A5 Digital Di­
vider Assembly.
d Check for 12V, .3 ms, 1 PPS signal at A19A1P1(5). If
incorrect or not present, check circuit of A19A1U1.
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