Model 456A
Section IV
Pa ragraphs 4-1 [0 4-5
SECTI ON
IV
MAINTENANCE
4-1 .
G ENERAL.
The Mode1 456A should require very littl e maintenance.
It is built w ith etched circuit wi ring and transistors
which should ens ure long; trouble-free life . However,
should trouble occur special care must be taken in
s ervicing to a void damage to the (ransistors or the
etched circuit board.
REPLAC ING TRA NSISTORS.
The transistors are
soldered in: substitution of transistors should not be
resorted to unless there is some indication that they
are fa ulty. Unless extreme care is taken when solder
ing, the transistor may be damaged. See figu re
4-1.
CAUTION
Be careful not to short voltages across th e
transistors .
Small bias changes may ruin
a transistor due to excessive dissipation.
Be sure to turn the unit off before doing any
soldering. A smaUleakage current from the
iron applied at the input may exceed ratings
on the transistors at the output.
Components with in
�
i nstruments a re conserva tively
operated to provide maximum ins trument reliability.
In spi te of this , parts within an ins trument may fail.
Usually, the instrument must be immedia tely repaired
with a minimum of "down time".
A s ystematic
approach can greatly simplify and thereby speed up
the repair.
Specifications for the Model 456A
AC
Current Probe
are given in table 1-1 . The procedures in this manual
give additi onal tests and the data they contain are not
to be considered as s pecifica tions .
Your Hewlett-Packard representa tive maintains com
plete facilities and specially trained personnel to
a ssist you with any engineering, applictttion, tests,
or repair problems you may have with Hewlett
Packard ins truments .
4-2.
CABIN E T REMO V Al.
CAUTION
Remove power cord from receptacle if unit
is equipped with ac s upply.
The instrument may be taken from the cabinet by
remOVing the two sc rews at the rear of the instrument
and pulling the cabinet loose from the front panel a nd
side frames.
4-3.
O P �R AT IO N O N 230 VO LT AC.
The Model 456A is normally wired for 1 15 volt oper
ation unless otherwise specified. It can be quickly
and easily converted to operate from a nominal line
00395-1
voltage of either 11 5 or 230 volts and a frequency of
50 to 1 000 cps . To convert for 230-volt opera tion
remove the short across R 90. Tu rn the instrument
off before doing any soldering.
4- 4 .
C HEC KI N G
THE
BATT E R IES.
Whenever trouble is encountered check the voltage a t
the BATTERY TEST terminals. If this VOltage is
below 7 vol ts replace all of the batteries . The B AT
TER Y TEST terminals are across only pa rt of the
batteries . F or this reason all of the batteries should
be replaced if the voltage is below 7 vol ts . If some
of the ba tteries are depleted the remaining batteries
are proba bly low also. In addition, the batteries acrOSs
the BATTERY
TEST
jacks could
be
fresh while �he
other battery could be depleted. If trouble is en
countered, remove the cabinet and test the voltage
of BT3 also. Th is voltage should be at least 4.7 volts .
Discard battery if lower.
WARNING
Mercury ba tteries generate hydrogen gas at
the end of thei r l ife or when they a re shorted .
Hydrogen gas is highly explos ive and may be
exploded by the heat of the battery. Observe
the following precautions when us ing mercury
ba tteries.
1) Never discha rge a mercury-cell battery
after its voltage falls below 7D% of its nominal
voltage, or when it fa ils to operate the equip
ment in which i t is used .
2) Never place a direct short ac ross a
mercury cell battery.
3)
Never leave the
POW
ER switch
ON
w hen
the equipment is not in use, or a fter the
battery fails to operate the equipment.
4)
Never retain exhaus ted mercury -cell bat
teries . Discard dead batteries as soon as
possible. Discard in ga rbage, NOT in was te
basket. if batterv is incinerated. in addition
to the explosive haza rd, mercury vapor is
EXTREMEL Y TOXIC.
DO
NOT INCINERATE.
5) Store spare mercury-cell batteries in a
cool, adequately ventilated area .
4-5 .
RE P LAC I N G THE BAT TER I E S .
Whenever the voltage at the BATTERY TEST termi
nals falls below 7 volts or if the batteries are sus
pected, replace the batteries. Turn (he ins trument
OFF.
Remove the cabinet as instructed in paragraph
4-2. Remove and disca rd all ba tteries. Replace the
batteries with one Mallory Type
TR
234 battery or
4-1
