HP 437B User manual

HP 437B
SERVICE MANUAL
HP 437B
POWER METER
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HP
Part
No.
00437-90016
E1088
HEWLETT
HP
Binder
Part
No.
9282-1077
GQ
PACKARD
aZer dH

SERVICE MANUAL
HP 437B
POWER METER
SERIAL NUMBERS
This manual applies to instruments with serial
numbers prefixed 2801A and above.
For additional important information about serial
numbers, see INSTRUMENTS COVERED BY
THIS MANUAL in Section 1.
OD | HEWLETT
LE PACKARD
© Copyright HEWLETT-PACKARD COMPANY 1988
1501 PAGE MILL ROAD, PALO ALTO, CALIFORNIA, U.S.A.
SERVICE
MANUAL
PART
NO.
00437-90016
E1088
Microfiche
Service
Manual
Part
No.
00437-90018
Operating
Manual
Part
No.
00437-90015
Microfiche
Operating
Manual
Part
No.
00437-90017
Getting
Started
Guide
Part
No.
00437-90014

HP 437B
CERTIFICATION
Hewlett-Packard
Company
certifies
that
this
product
met
its
published
specifications
at
the
time
of
shipment
from
the
factory.
Hewlett-Packard
further
certifies
that
its
calibration
measurements
are
traceable
to
the
United
States
National
Bureau
of
Standards,
to
the
extent
allowed
by
the
Bureau’s
calibration
facility,
and
to
the
calibration
facilities
of
other
International
Standards
Organization
members.
WARRANTY
This
Hewlett-Packard
instrument
product
is
warranted
against
defects
in
material
and
workmanship
for
a
period
of
one
year
from
date
of
shipment.
During
the
warranty
period,
Hewlett-Packard
Company
will,
at
its
option,
either
repair
or
replace
products
which
prove
to
be
defective.
For
warranty
service
or
repair,
this
product
must
be
returned
to
a
service
facility
designated
by
HP.
Buyer
shall
prepay
shipping
charges
to
HP
and
HP
shall
pay
shipping
charges
to
return
the
product
to
Buyer.
However,
Buyer
shall
pay
all
ship-
ping
charges,
duties,
and
taxes
for
products
returned
to
HP
from
another
country.
HP
warrants
that
its
software
and
firmware
designated
by
HP
for
use
with
an
instrument
will
execute
its
programming
instructions
when
properly
installed
on
that
instrument.
HP
does
not
warrant
that
the
operation
of
the
instrument,
or
software,
or
firmware
will
be
uninterrupted
or
error
free.
LIMITATION OF WARRANTY
The
foregoing
warranty
shall
not
apply
to
defects
resulting
from
improper
or
inade-
quate
maintenance
by
Buyer,
Buyer-supplied
software
or
interfacing,
unauthorized
modification
or
misuse,
operation
outside
of
the
environmental
specifications
for
the
product,
or
improper
site
preparation
or
maintenance.
NO
OTHER
WARRANTY
IS
EXPRESSED
OR
IMPLIED.
HP
SPECIFICALLY
DISCLAIMS
THE
IMPLIED
WARRANTIES
OF
MERCHANTABILITY
AND
FITNESS
FOR
A
PARTICULAR
PURPOSE.
EXCLUSIVE
REMEDIES
THE
REMEDIES
PROVIDED
HEREIN
ARE
BUYER’S
SOLE
AND
EXCLUSIVE
REMEDIES.
HP
SHALL
NOT
BE
LIABLE
FOR
ANY
DIRECT,
INDIRECT,
SPE-
CIAL,
INCIDENTAL,
OR
CONSEQUENTIAL
DAMAGES,
WHETHER
BASED
ON
CONTRACT,
TORT,
OR
ANY
OTHER
LEGAL
THEORY.
ASSISTANCE
Product
maintenance
agreements
and
other
customer
assistance
agreements
are
available
for
Hewlett-Packard
products.
For
any
assistance,
contact
your
nearest
Hewlett-Packard
Sales
and
Service
Office.
Addresses
are
provided
at
the
back
of
this
manual.
WARRANTY 5

HP 437B
HP 437B
Herstellerbescheinigung
Hiermit
wird
bescheinigt,
dass
dieses
Gerit/System
in
Uber-
einstimmung
mit
den
Bestimmungen
von
Postverfiigung
1046/84
funkenstort
ist.
Der
Deutschen
Bundespost
wurde
das
Inverkehrbringen
dieses
Gerates/Systems
angezeigt
und
die
Berechtigung
zur
Uberpriifung
der
Serie
auf
Einhaltung
der
Bestimmungen
eingeraumt.
Zusatzinformation fiir Mess- und Testgeriite:
Werden
Mess-
und
Testgerite
mit
ungeschirmten
Kabeln
und/
oder
in
offenen
Messaufbauten
verwendet,
so
ist
vom
Betreiber
sicherzustellen,
dass
die
Funk-Entstérbestimmungen
unter
Be-
triebsbedingungen
an
seiner
Grundstiicksgrenze
eingehalten
werden.
Manufacturer’s Declaration
This
is
to
certify
that
this
product
meets
the
radio
frequency
interference
requirements
of
Directive
FTZ
1046/1984.
The
German
Bundespost
has
been
notified
that
this
equipment
was
put
into
circulation
and
has
been
granted
the
right
to
check
the
product
type
for
compliance
with
these
requirements.
Note:
If
test
and
measurement
equipment
is
operated
with
unshielded
cables
and/or
used
for
measurements
on
open
set-ups,
the
user
must
ensure
that
under
these
operating
conditions,
the
radio
frequency
interference
limits
are
met
at
the
border
of
his
premises.
6 MANUFACTURER'S DECLARATION

Warning ip
Safety Considerations
This product and related documentation must be reviewed for
familiarization with safety markings and instructions before operation.
This product is a Safety Class I instrument (provided with a protective earth
terminal).
Before Applying Power
Verify that the product is set to match the available line voltage and the
correct fuse is installed.
Safety Earth Ground
An uninterruptable safety earth ground must be provided from the main
power source to the product input wiring terminals, power cord, or supplied
power cord set.
Any interruption of the protective (grounding) conductor (inside or outside the
instrument) or disconnecting the protective earth terminal will cause a
potential shock hazard that could result in personal injury. (Grounding one
conductor of a two conductor outlet is not sufficient protection.) In addition,
verify that a common ground exists between the unit under test and this
instrument prior to energizing either unit.
Whenever it is likely that the protection has been impaired, the instrument
must be made inoperative and be secured against any unintended operation.
If this instrument is to be energized via an autotransformer (for voltage
reduction) make sure the common terminal is connected to neutral (that is, the
grounded side of the mains supply).
Servicing instructions are for use by service-trained personnel only. To avoid
dangerous electric shock, do not perform any servicing unless qualified to do
sO.
Adjustments described in the manual are performed with power supplied to the
instrument while protective covers are removed. Energy available at many
points may, if contacted, result in personal injury.
Capacitors inside the instrument may still be charged even if the instrument
has been disconnected from its source of supply.
SAFETY CONSIDERATIONS 7

HP 437B
Warning 7
Caution db
For
continued
protection
against
fire
hazard.
replace
the
line
fuse(s)
only
with
250V
fuse(s)
of
the
same
current
rating
and
type
(for
example,
nomial
biow,
time
delay,
etc.).
Do
not
use
repaired
fuses
or
short
circuited
fuseholders.
Safety Symbols
symbol when it is necessary for the user to refer to the instruction
manual (see Table of Contents for page references).
(
Instruction
manual
symbol:
The
product
will
be
marked
with
this
5 Indicates hazardous voltages.
9 Indicates earth (ground) terminal.
The WARNING sign denotes a hazard. It calls attention to a procedure,
practice, or the like, which, if not correctly performed or adhered to, could
result in personal injury. Do not proceed beyond a WARNING sign until the
indicated conditions are fully understood and met.
The CAUTION sign denotes a hazard. It calls attention to an operating
procedure, practice, or the like, which, if not correctly performed or adhered
to, could result in damage to or destruction of part or all of the product. Do
not proceed beyond a CAUTION sign until the indicated conditions are fully
understood and met.
8 SAFETY CONSIDERATIONS
@

ADJUSTMENTS
5-1. Introduction
5-2. Safety
Considerations
Warning Va
5-3. Equipment
Required
5-4. Factory Selected
Components
This
section
contains
adjustments
and
checks
that
ensure
proper
performance
of
the
Power
Meter.
Adjustments
are
not
required
on
any
fixed
periodic
basis,
and
normally
are
performed
only
after
a
performance
test
has
indicated
that
some
parameters
are
out
of
specification.
Performance
tests
should
be
completed
after
any
repairs
that
may
have altered
the
characteristics
of
the
instrument.
The
test
results
will
make
it
possible
to
determine
whether
or
not
adjustments
are
required.
Allow
30
minutes
for
the
Power
Meter
to
warm
up,
and
then
remove
the
top
and
bottom
covers,
for
access
to
the
test
and
adjustment
points.
To determine which performance tests and adjustments to perform after a
repair, refer to paragraph 5-5, Post-Repair Adjustments.
This
section
contains
a
warning
that
must
be
followed
for
your
protection
and
to
avoid
damage
to
the
equipment
being
used.
Adjustments described in this section are performed with power applied to the
instrument and with protective covers removed. Maintenance should be
performed only by trained personnel who are aware of the hazards involved.
When the maintenance procedure can be performed without power, the power
should be removed.
Most of the adjustment procedures include a list of recommended test
equipment. The test equipment is also identified on the test setup diagrams.
If substitutions must be made, the equipment used must meet the critical
specification listed in Table 1-3 in Section I.
Factory selected components are identified on the schematics and parts lists
by an asterisk(*) which follows the reference designator. The nominal value
of the selected component is shown. Table 5-1 lists the reference designator,
the service sheet where the component is shown, the value range, and the
basis for selecting a particular value.
ADJUSTMENTS 5-1

HP 437B
Make adjustments only in the order specified.
Note 4%
5-5.
Post-Repair
Table
5-2
lists
the
adjustments
related
to
repairs
or
replacement
of
any
of
the
Adjustments
assemblies.
Table 5-1. Factory Selected Components
Reference
Service
Range
of
Basis
of
Selection
Designator
Sheet
Values
A4R73
A4C
8252
1.
If
the
reference
power
is
outside
the
A4VR3
with
5.11V
range
of
1.000
+/-
0.007
mW
between
OC and 5SC, and if the A4R73,
A4VR3 combination is 825 Q
& 5.11V then change the A4R73,
A4VR3 combination to
1470 2 & 8.25V. However, if the
' A4R73, A41VR3 combination is
already 1470 2 & 8.25V, then a
problem exists elsewhere.
Zener or
1470 Q with
8.25V Zener
combination
Table 5-2. Post-Repair Adjustments, Tests, and Checks
Assembly Related Adjustments or Reference
Repaired Performance Test Service
Sheet
Al Display None A3B
A2 Keyboard None A3B
A3 Central Processing Unit 4-7, 4-8 A3A-A3C
A4 Analog Assembly 4-8, 4-9, 5-6, 5-7, 5-8, 5-9 A4A-A4C
(Includes Ref Oscillator)
50 MHz Reference Oscillator 4-10, 5-8, 5-9 A4C
(Part of Analog Assembly)
5-2 ADJUSTMENTS

HP 437B
5-6. 220 Hz
Frequency
Adjustment
Reference
Description
Equipment
Procedure
Service Sheet A4C
The 220 Hz is adjusted for maximum Power Meter readout.
RANGE
POWER METER CALIBRATOR
POWER METER
Figure 5-1. 220 Hz Frequency Adjustment Setup
Range Calibrator ..........c.ccccececesceteceeeceseeceenenssnaeeeees HP 11683A
1. Turn on both the Power Meter and the range calibrator. Set the range
calibrator controls as follows:
LINE: eiceccded ox dh eede ve bees vee ee eednatntels oeescu dee eve eee seed ee ees nana des ON
RANGE \0).0.55 cavgda vob ea @iaks outer ote aicandie eas ae Sadan coaagaaassireces 1 mW
FUNCTION (sie cv sess cities tales tia syrnie Sands ole a oye bow daly Saree eclp tele oe STANDBY
POLAREDY © si osc seco Resin diioas sieves liot ei sed oud vadewsekewee NORMAL
2. Connect the range calibrator to the Power Meter as shown in Figure
5-1.
3. Press the PRESET/LOCAL key, then the ENTER key.
ADJUSTMENTS 5-3

HP 437B
4. Press the ZERO key on the Power Meter, and allow time (5 to 15
seconds) for the Power Meter zeroing routine to finish.
5. Set the range calibrator’s FUNCTION switch to CALIBRATE.
6. Press the Power Meter’s CAL (SHIFTed ZERO) key.
7. Using (2). (+), Co), or G2, modify the REF CF to read 100.0%.
8. Press the ENTER key.
9. Adjust A4R87 (FREQ) for the maximum front panel reading.
5-4 ADJUSTMENTS

HP 437B
5-7. Ranges 4
and 5 Shaper
Adjustment
Reference Service Sheet A4A
Description Ranges 4 and 5 Shaper circuits are adjusted for proper gain.
' RANGE
POWER METER See
POWER METER
Figure 5-2. Ranges 4 and 5 shaper Adjustment Setup
Equipment Range Callbrator ¢ scien cincs sor eel a tea eaeavarco ws teadandeeatnes yecte HP 11683A
Procedure
1. Connect range calibrator to the Power Meter as shown in Figure 5-2.
2. Set the range calibrator controls as follows:
INE tik es be tetas iPS Foes led hee aatenite aelds nasiek deus ba wa Macealasegadns ON
RANGE: fe scost ib ide ssadaa fica tioia'ds eaeeas couse toned dows dade netic’ s | mW
FUNCTION cecjekd eyiedidage karst tena aatanteedi es tee nieeygeteaacit STANDBY
POGARULY” 302i ce-ch ten reek bad Behe ieee tls PEN has Sy a Sod NORMAL
@ 3. Press the Power Meter’s LINE switch to ON.
ADJUSTMENTS §-5

HP 437B
5-6
ADJUSTMENTS
10.
11.
12.
13.
14.
Press the PRESET/LOCAL key, then the ENTER key.
Press the ZERO key, and allow time (5-15 seconds) for the zeroing
routine to finish.
Set the range calibrator’s FUNCTION switch to CALIBRATE.
Press the Power Meter’s CAL (SHIFTed ZERO) key.
Using (<), (+), GD, or CO), modify the REF CF to read 100.0%
Press the ENTER key.
Set the range calibrator’s RANGE to 10 mW.
Adjust A4RI11 (RNG 4 SHP) for a reading of 10.00 +0.0!1 mW on the
Power Meter display.
Set the range calibrator’s RANGE to 100 mW.
Adjust A4R112 (RNG 5 SHP) for a reading of 100.0 +0.1 mW on the
Power Meter display.
Repeat steps 10 through 13 to check that interaction between steps has
not caused a shift in settings.

HP 437B
@
5-8. Power
Reference
Frequency
Oscillator
Adjustment
Note
Reference
Description
Equipment
rk Adjustment of the Power Reference Oscillator frequency may also affect the
a
|
output
level
of
the
oscillator.
Thus,
after
the
frequency
is
adjusted
to
50.0
+0.5 MHz, the output level should be checked as described in Section 4. A
procedure
for
adjusting
the
output
to
the
specified
level
is
provided
in
the
next paragraph.
Service Sheet A4C
Variable inductor A4L5 is adjusted to set the power reference oscillator
output frequency to 50.0 +0.5 MHz.
HP 4378
POWER METER
FREQUENCY
COUNTER
POWER REF
1.00 mW SO MHz
Figure 5-3. Power Reference Oscillator Frequency Adjustment Setup
Frequency Counter .......... ccc cece cece eee e een e een eeees HP 5328A Option 031
ADJUSTMENTS 5-7

HP 437B
Procedure
5-8
ADJUSTMENTS
Connect
the
equipment
as
shown
in
Figure
5-3.
Set
up
the
counter
to
measure
frequency.
Set the Power Meter LINE switch to ON.
Press the PRESET/LOCAL key, then the ENTER key.
Press the PWR REF (SHIFTed (J) key.
Observe
the
indication
on
the
frequency
counter.
If
it
is
50.0
+0.5
MHz
no
adjustment
of
the
power
reference
oscillator
frequency
is
necessary.
If
it is
not
within
these
limits,
adjust
the
power
reference
oscillator
frequency
as
described
in
steps
6
and
7.
y
Remove the Power Meter bottom cover.
Adjust A4L5 (FREQ) to obtain a 50.00 +0.5 MHz indication on the
frequency counter.

HP 437B
5-9. Power
Reference
Oscillator
Level
Adjustment
Reference
Description
Note UE |
HP 437B
POWER METER
POWER REF
1.00 mW 50 MHz
es a =m,
QODdQdo0|O0C0O
20 Beecboo| | |
Service Sheet A4C
The power reference oscillator is factory-adjusted to 1.0 mW +0.7% using a
special measurement system accurate to 0.5% traceable to the National
Bureau of Standards and allowing for a 0.2% transfer error. To ensure
maximum accuracy in readjusting the power reference oscillator, the
following procedure provides step-by-step instructions for using specified
Hewlett-Packard instruments of known capability. If equivalent instruments
are used, signal acquisition criteria may vary and reference should be made
to the manufacturer’s guidelines for operating the equipment.
The Power Meter may be returned to the nearest HP office to have the
power reference oscillator checked and/or adjusted. Refer to Section 2,
PACKAGING.
HP _ 432A
POWER METER
meve DIGITAL VOLTMETER
THERMI STOR
MOUNT
Figure 5-4. Power Reference Oscillator Level Adjustment Setup
ADJUSTMENTS 5-9

HP 437B
Equipment
Procedure
5-10
Note
ADJUSTMENTS
Test Power Meter......0 0.0. c cece cece tee eeaeeeeeeeeeneens HP 432A
Thermistor Mount...........cc ccc cece cee cececceeveeuceseugeees HP 478A-H75
Digital Voltmeter (DVM)...... 0.0.0... cece ev cceccceeaeacuceeneneuegs HP 3456A
1. Set up the DVM to measure resistance. Connect the DVM between the
>
9.
10.
Vrf connector on the rear panel of the test power meter and pin | on
the thermistor mount end of the test power meter interconnect cable.
Round off the DVM indication to two decimal places and record this
value as the internal bridge resistance (R) of the test power meter
(approximately 200 ohms).
R (Internal Bridge Resistance)
Connect the test power meter to the Power Meter as shown in Figure
5-4.
Set the Power Meter LINE switch to ON. Ensure that the PWR REF is
off. Wait thirty minutes for the test power meter thermistor mount to
stabilize before proceeding to the next step.
4
Set the test power meter range switch to coarse zero and adjust the @
front panel coarse zero control to obtain a zero meter indication.
Fine zero the test power meter on the most sensitive range, then set the
power meter range switch to 1 mW.
rT) Ensure that the DVM input leads are isolated from chassis ground when
oF performing the next step.
Set up the DVM to measure microvolts.
Connect the positive and negative input leads, respectively, to the
Vcomp and Vrf connectors on the rear panel of the test power meter.
Observe the indication on the DVM. If less than 400 microvolts, proceed
with the next step. If 400 microvolts or greater, press and hold the test
power meter fine zero switch and adjust the coarse zero control so that
the DVM indicates 200 microvolts or less. Then release the fine zero
switch and proceed to the next step.
Round off the DVM indication to the nearest microvolt and record this
value as VO.
vw

HP 437B
11. Disconnect the DVM negative input lead from the Vrf connector on
the test power meter and reconnect it to chassis ground.
12. Press the PWR REF (SHIFTed (7_)) key to turn the reference oscillator
on.
13. Record the indication observed on the DVM as Vcomp.
Vcomp
14, Disconnect the DVM negative input lead from chassis ground and
reconnect it to the Vrf connector on the rear panel of the test power
meter. The DVM is now set up to measure V1 which represents the
power reference oscillator output level.
15. Calculate the value of V1 equal to | mW from the following equation:
Vi — Yo = Voomp — V (Vcomp)? — (10-8) (4R) (EFFECTIVE EFFICIENCY)
Where:
Vo = previously recorded value
Vcomp = previously recorded value
10-3 = 1 milliwatt
R = previously recorded value
EFFECTIVE value for thermistor mount at 50 MHz
EFFICIENCY (traceable to the National Bureau of Standards).
16. Remove the Power Meter’s top cover and adjust A4R114 (LEVEL) until
the DVM indicates the calculated value of V1.
ADJUSTMENTS 5-1]

HP 437B
Typical
Calculations
5-12
ADJUSTMENTS
ACCURACY:
DVM Measurements: (Vcomp) +0.018%
(V; — Vo) +0.023%
(R) +0.03%
Math Assumptions: +0.01%
EFFECTIVE EFFICIENCY CAL (NBS): +0.5%
MISMATCH UNCERTAINTY: +0.1%
(Source and Mount SWR <1.05) <+0.7%
MATH ASSUMPTIONS:
ae 2Vcomp (V1 — Vo) + Vo? — Vi?
RF “ (4R) (EFFECTIVE EFFICIENCY)
Assume: Vp*— V,2 = (V; — Vo)?
= (V; =Vg) 7 oe -V,2 + 2V, = Vo?
Want: Vo2 — V,?
«error = (V,2 + 2V, Vo — Vo2) — (Vo? — V2)
if 2V9 (Vi — Vo) < 2Veomp (Vi — Vo) i-e., Vo < Veomp:,
error is negligible.
Vcomp ~ 4 volts. If Vo < 400 xV, error is < 0.01%.
(Typically Vp can be set to <50 nV).
Derivation of Formula for V,; — Vo
eee: 2Vcomp (V, — Vo) + Vo? — Vi?
RF “ (4R) (EFFECTIVE EFFICIENCY)
Desired Ppp = 1 mW = 1073
2Vcomp (V; — Vo) + Vo? — Vi?
= 10-3 SS
(4R) (EFFECTIVE EFFICIENCY)
Let (4R) (EFFECTIVE EFFICIENCY) (1078) = K
Substitute — (V, — Vo)? for Vo? — V,? (see Math Assumptions under Accuracy).
Then 0 = (V,— Vo)? — 2Vcomp (V; — Vo) + K
or V;) — Vo = Vcomp — V_ (Vcomp)? — K

SERVICE
8-1. General
Information
8-2. Service Sheets
8-5. Safety
Considerations
This section contains information required for servicing the Power Meter. It
includes block diagrams with theory and troubleshooting, schematic diagrams,
and schematic diagram notes.
The foldout pages in the last part of this section are called the service sheets
(SS). They contain block diagrams, schematic diagrams, supplemental
diagrams, and associated information.
8-3. Block Diagrams
The block diagram and related service information is found on Service Sheet
BD1. BDI is an overall block diagram that shows major functional sections
of the Power Meter. It serves as an index to the more detailed information
on the succeeding service sheets and is the starting point for most trouble
shooting procedures.
8-4. Schematic Diagrams
Service Sheet | is a detailed block diagram and mechanical assembly drawing
of the Al Display Assembly and the A2 Keyboard Assembly. These
assemblies are replaced as assemblies only, and SS1 is provided to show
interconnects between these assemblies and the A3 Digital board. The
schematic diagrams and their related information are presented in the
additional seven Service Sheets A3a, A3b, A3c, A3d, and Ada, A4b, Adc.
These diagrams, in functional groupings, are designed to aid in understanding
the principles of operation and to aid in troubleshooting the Power Meter.
Before applying power, verify that the instrument is properly set to operate
from the available line voltage and that the correct fuse is installed. An
uninterrupted safety earth ground must be provided from the main power
source to the instrument input wiring terminals, power cord, or supplied
power cord set.
SERVICE 8-1

HP 437B
8-2
Warning ie
Caution mm
SERVICE
8-6. Warnings and Cautions
Pay attention to the WARNINGS and CAUTIONS. They must he followed
for your protection and to avoid damage to the equipment.
Maintenance described herein must be performed with power supplied to the
instrument and with the protective covers removed. Such maintenance should
be performed only by service trained personnel who are aware of the hazards
involved (for example, fire and electrical shock). Where maintenance can be
performed without power applied, the power should be removed.
Any interruption of the protective (grounding) conductor (inside or outside of
the instrument), or disconnection of the protective earth terminal will create a
potential shock hazard and could result in personal injury. Grounding one
conductor of a two-conductor outlet is not sufficient. Whenever it is likely
that the protection has been impaired, the instrument must be made
inoperative (i.e., secured against unintended operation).
If the instrument is to be energized via an autotransformer (for voltage
reduction), make sure the common terminal is connected to neutral (that is,
the grounded side of the mains supply).
Make sure that the 250 volt normal-blow fuses with the specified current
rating are used for replacement. Do not use repaired fuses or short- circuited
fuse holders. To do so could create a shock or fire hazard.
Some printed circuit boards contain devices that may be damaged if the
board is removed or installed while the power is on. Verify that the LINE
switch is OFF or that the power cord is unplugged before you remove or
install a printed circuit board.
After removing devices from sockets, store the devices with the pins in
conductive foam. This will prevent accidental damage from a static
discharge.