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Model 456A
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 ta ken in
s ervicing to a void damage to the (ransistors or the
etched circ uit boa rd.
REPLAC ING TRA NSISTORS.
soldered in: substitution of transis tors should not be
resorted to unless there is some indication that they
a re fa ulty. Unless extreme care is taken when solder
ing, the transistor may be damaged. See figu re 4-1.
CAUTION
Be ca reful not to short voltages across th e
transistors .
Small bias changes may ruin
a tran sistor due to excessive dissipation.
Be sure to turn the unit off before doing any
solde ring. A smaUleaka ge cur rent from the
iron applied at the input may exceed ratings
on the transi s tors at the output.
�
Components with in
i nstruments a re conserva tively
operated to provide maximum ins trument reliability .
I n spi te o f this , parts within an ins trument may fail.
Usually , the instrument must be immedia tely repaired
with a minimu m of "down time".
approach can grea tly simplify and thereby s peed up
the repair.
Specifications for the Model 456A
are given in table 1-1 . The procedu res in this manual
give addi ti onal tests and the data they contain are not
to be considered as s pecifica tions .
You r Hewlett-Packard representa tive main tains com
plete facili ties and s pec ially 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.
CAU T ION
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 rea r of the instrumen t
and pulling the cabinet loose from th e front panel a nd
side frames.
4-3.
O P �R AT IO N O N 230 V O LT AC.
The Model 456A is normally wired for 1 15 volt oper
a tion unless otherwise specified.
and easily converted to operate from a nominal line
00395-1
SECTI ON
MAINTENANCE
The transistors are
A s ystematic
Current P robe
AC
It can be quickly
IV
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.
off before doing any soldering .
C HEC KI N G THE BATT E R IES.
4 - 4 .
Whenever trouble is encountered chec k the voltage a t
the BATTERY TEST term inals.
below 7 vol ts replace all of the batte ries . The B AT
TER Y TEST terminals are across only pa rt of the
batteries .
F or this rea son all of the batteries should
be replaced i f th e voltage is below 7 vol ts . If some
of the ba tte ries are depleted the remaining batte ries
are proba bly low also. In addition, the batteries ac rOSs
TEST
the BATTERY
jacks could
o ther batte ry could be depleted.
countered, remove the cabinet and test the voltage
of BT3 also. Th is voltage should be at lea s t 4.7 volts .
Discard batte ry if lowe r.
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) N ever discha rge a mercury-cell battery
after its voltage falls below 7D% of i ts nom inal
voltage, or when it fa ils to operate the equip
ment in which i t is u sed .
2) Never place a direct short ac ross
me rcury c ell battery.
POW
3) Nev er leave the
th e 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 a s
poss ible.
Discard i n ga rbage, N OT in was te
bas ket.
if batterv is incinerated. in addition
to the explosive ha za rd, mercury vapor is
EXTREMEL Y TOXIC .
5) Store spare mercury-c ell batteries in a
cool, adequately ventilated area .
4-5 .
RE P LAC I N G T HE BA T TER I E S .
Wheneve r the voltage at the B ATTERY TEST termi
nals falls below 7 volts or if the batteries are s us
p ected, replace the batteries.
OFF.
Remove the cabinet as instructed in paragraph
Remove and disca rd all ba tteries. Replac e the
4-2.
batteries with one Mallory Type
Section IV
Pa ragraphs 4-1 [0 4 - 5
Tu rn the instrument
If this VOltage is
be
fresh while �he
If trouble is en
a
ON
ER s witch
w hen
DO
NOT INCINERATE.
Turn (he ins trument
TR
234 battery or
4- 1
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