RCA WV-38A Manual

SUGGESTED PRICE 5QCENTS
operatingand
maintenanceinstructions

RCA Volt-Ohm-Milliammeter
SafetyPrecautions
For properoperation,theground(black)leadofthe WV-38A
should beconnectedtothegroundoftheequipmentunder test, before
anyotherconnectionsaremade.Animportantpointtorememberis
that there isalwaysdangerinherentintestingelectricalequipment.
Therefore, theoperatorshouldthoroughly familiarize himself with the
equipmentunder test before working onit,bearingin mind that high
voltagesmayappearatunexpectedpointsindefectiveequipment. Addi-
tional precautions which experienceintheindustryhasshowntobe
importantarelistedbelow:
1.Itisgoodpracticetoremovepowerbeforeconnecting test leads
tohigh-voltagepoints.Ifthisisimpractical,beespeciallycarefulto
avoid accidentalcontact with equipmentracksandotherobjects which
can providea ground. Working with onehandinyourpocketandstand-
ing ona properlyinsulated floor lessensthedangerofshock.
2. Filter capacitorsmaystorea chargelargeenoughtobelethal.
Therefore, discharge filter capacitorsbeforeattaching test leads.
3. Remember that leads with brokeninsulationprovidetheaddi-
tional hazardofhighvoltagesappearingatexposedpointsalongthe
leads.Check test leadsforfrayedorbrokeninsulationbefore working
with them.
4. Tolessenthedangerofaccidentalshock,disconnect test leads
immediately after test iscompleted.
5.Remember that the risk ofsevereshockis only oneofthepos-
sible hazards. Even a minorshockcanplacetheoperatorinjeopardyof
moreseriousrisks,suchasa bad fall orcontact with a sourceofhigher
voltage.
6.Theexperiencedoperatorcontinuouslyguardsagainstinjury
anddoesnotworkonhazardouscircuitsunlessanotherpersonis avail-
abletoassistincaseofaccident.
3/71
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RCA Volt-Ohm-Milliammeter
Description
The RCA WV-38A Volt-Ohm-Milliammeter isa completelyportable,
all-purposemeasuringinstrument.The WV-38A will measurermsvaluesof
AC sine-wavevoltages from 0.1 volt to5000volts;DCvoltages from 0.005
volt to5000volts;DCcurrent from 1 microampereto10amperes;resistance
from 0.2ohmto20megohms;anddecibels from —20dbto+50db.Input
resistanceis20,000ohms-per-voltonDC,and5000ohms-per-voltonAC.
Featuresofthisversatile test instrumentincludetheuseofprecision
resistorsinallmeasuringcircuits,anda large,easy-to-readmeter with
sensitive 50/zA movement.Thepanelhasbeenspeciallydesigned with
two-color markingsfor simplified operation.*
A convenientfunctionswitchisprovided with AC, +DC,and—DC
positions. The+DCand —DC positionsofthisswitchreversethepolarity
of the test leads—afeature that isalso helpful incheckingthefront-to-back
resistanceratioofelectrolyticcapacitorsandmanytypesofsemi-conductor
devices.
Two special silicon diodesareusedtoprotectthemetermovement
againstburnoutduetoaccidentaloverload.*A fuseprotectstheprecision
multiplier intheohmsnetwork.
The WV-38A iscompletelyportable,requiringnoexternalpower
source. Five internalbatteries(notprovided)areusedfortheohmsfunction
(4penlightcellsand1 "D"-size flashlight cell). Theunitweighs only 3V2
pounds,andmeasures6%inchesby5^4inchesby SVs inches.Convenient
clips areprovidedonthehandleforcarryingthe test leads.The WV-38A
is attractivelystyled, with a rugged,lightweight,bakelitecase.
^Included on wired instruments with serial numbers above 20,000, andon kits with
serial numbers above 66,000 K.
Items Supplied with WV38A
1—RedTest Lead andProbe1—BlackTest Lead with Alligator
1—Slip-on Alligator Clip andRed Clip and Black Boot
Boot 1—Warranty- Registration Card
1—Instruction Book
(BatteriesNotSupplied)
Available Accessories forWV-38A
WG-297 High VoltageProbe
WG-210 Resistor900 Megohm forH.V.Probe(10x multiplier for5000
V. range)
WG-211 Resistor495 Megohm for H.V. Probe(100x multiplier for250
V. range)
WG-270A Vinyl Carrying Case
3

RCA Volt-Ohm-Milliammeter
Specifications
Electrical
DC Voltmeter (at full scale):
Ranges 0 to .25, 1.0, 2.5,10,50,250,1000,5000volts
Inputresistance20,000ohms-per-volt
Circuit loading 50 microamperesbleedercurrent
Accuracy ±3%
AC Voltmeter (at full scale):
Ranges .. .." ...0to 2.5, 10,50, 250,1000,5000volts
InputResistance5000ohms-per-volt
Circuit loading200microamperesbleedercurrent
Accuracy ±5%
Frequency Response(reference1000cps)flat within *4db
from 10cpsto50kconthe2.5,10,and50 volt ranges.
DC Current (at full scale):
0 to 50microamperes
0 to 1 milliampere
¥?o«Mo 1 0to 10milliamperes
Kanges•• ' " " ^ 0 to100 milliamperes
0 to 500milliamperes
0 to 10 amperes
Insertion Loss .0.25 volt
Accuracy ±3%
DC Ohms:
Ranges ScaleEndsCenterScale Full ScaleCurrents
R X10-200012ohms 120 MA
R X1000-200,0001200ohms MA
R X 10,0000-20,000,000120,000ohms 0.06 MA
Accuracy ±3°of pointerposition for exactvalue
Internal Batteries:
RX1 SizeD Cell, 1% volts
R X 100 Size D Cell, iy2volts
R X 10,000 . .4 Penlite Cells in series with D cell, 7% volts
AF Output (at full scale):
Ranges 0 to 2.5, 10,50,250volts
InputResistance5000ohms-per-volt
Circuit Loading 200 microamperes
Accuracy ±5%
Note :
An internallyconnected 0.1 *ifDC blocking capacitorpermitsout-
put measurements in presence ofDC voltages.
4

RCA Volt-Ohm-Milliammeter
Decibel Levels (Zero DBis1 milliwatt in600 ohms) :
2.5V,range
10V.range
50V.range
250V.range
-20to+10DB
- 8to+22DB
+6to+36DB
+20to+50DB
(May bereadonOutputorACpositions)
Mechanical Specifications
Dimensions—(less handle)
Height
Width
Depth
Weight
. 6%inches
.5x/4 inches
:3Y$ inches
3l/2pounds
Meter Scales
Thereare five separate scalesonthemeter.Thetopblackscaleis
usedwhenmeasuringOhms.ThesecondblackscaleisusedtoreadDC
voltagesandcurrents.ThetworedscalesareusedwhenmeasuringAC
voltages,theloweronebeingused only forthe2.5V.range.Thebottom
scaleonthemeterisusedfordecibelmeasurements.A chart,located
atthelowerrighthandcornerofthescaleforconvenience,isusedwhen
making decibelmeasurements.
The Range Switch, locatedatthecenterofthecontrolpanel,has
12positions.TheRange Switch maybeturnedineitherdirectionto
obtain thefunctionandrangedesired.
The Function Switch locatedattheupperleft-handcornerofthepanel
has three positions, "AC", "+DC", and "—DC".
To measureallACVoltagesandtomakedecibelmeasurements,the
switch mustbesettothe "AC" position.
For positivedirectcurrentandDCvoltagemeasurements,theswitch
mustbesettothe"+DC"position.
9 The "—DC" positionreversesthepolarityofthe "—COMMON" and
"+"jacks,permittingdirectmeasurementofnegativedirectcurrentand
DC voltage. This switchpositioncanalsobeusedasa convenientmeansof
reversing thepolarityofthe test leadswhencheckingthefront-to-back
resistanceratioofelectrolyticcapacitorsandmanytypes ofsemiconductor
devices.
Range Switch
Function Switch

RCA Volt-Ohm-Milliammeter
Operating Section
Zero Setting of Pointer
Thepointerofthemetermustindicatezerowhenthe WV-38A isin
thenormaloperatingposition.Ifthepointer does notindicateZero,the
adjustmentscrewlocatedatthelowercenterofthemetercovershould
bereadjusted.
Useof Range andMeter Scales
Themeterscalesonthe WV-38A havebeendesignedtoprovide
ease ofoperationandquickreadabilityovera wide range ofmeasure-
ments.Scaleshavebeengroupedaccordingtothetypeofmeasurement
for which theyareused.
Becauseofthewidenumberofmeasurement ranges providedon
the WV-38A, itisoftenpossibletotakevoltageorresistancereadings
on two ranges andscales.For greatest accuracyinvoltageandcurrent
measurements,alwaysusethe range which will provideanon-scale
reading which is nearest tothefull-scalepoint.Forexample:48DC
Volts canbereadfromeitherthe50 Volt orthe250 Volt range.Because
the50 Volt range will providea reading nearest thefull-scalepoint,the
50 Volt range onlyshouldbeusedifa readingof best accuracyistobe
obtained.ThisgeneralruleappliestoallACandDCVoltageranges.
For resistancemeasurements,however,the range selectedshouldbethe
one which providesa reading nearest thecenterofthescale, because the
WV-38A providesthemostaccurateOhmsreadingsatmid-scalepoints.
For some measurements it will benecessarytousea multiplying
factor with thescaletoobtainthecorrectreading.Therequired multi-
plication isindicatedbythesettingofthe range switch.Forexample:
when the range switchissettothe1000V.positionforvoltagemeasure-
ment,the0 to10scaleisused,butthereadingis multiplied by100times.
CAUTION:
When makingvoltageorcurrentmeasurements,itisgoodpractice
tomakea trial measurementata higher range settingthanisconsid-
erednecessary, because repeatedoverloadmaydestroythemetermove-
mentorimpairtheaccuracyofindications.
Itisalsogoodpracticeforpersonalprotectiontoturnoffallpower
tothecircuitunder test whenconnectingordisconnectingthe test leads.
Thepowertothecircuitunder test mustbeturnedoffwhen in-circuit
resistance measurements aremade,otherwisedamagetothe WV-38A
mayresult.
6

RCA Volt-Ohm-Milliammeter
Figure1.D-CVoltageMeasurement
DC Voltage Measurement (SeeFig*1.)
1.Setthe AC-DC Switchtothe"+DC"or "—DC" positionasrequired.
2. SettheRangeSwitchtoa positionconsiderablyhigherthanthe
voltagetobemeasured.
3.Plugtheblack test leadintothe "—COMMON" jackonthecontrol
panel.
4.Plugthered test leadintothe"+"jackonthecontrolpanelwhen
the2.5V.,10V,,50V.,250V.or1000V., range isused.
5.Connectthe test leads tothevoltagesourc**^ bemeasured.
6.ResettheRangeSwitchtoa positionw ^ givesa suitablepointer
deflection.
7.ReadtheDCvoltagefromf1scalecorrespondingtothe range
selected.
Note: In rare applicationswherehighenergyrfis present, suchas measur-
ing dc"keep-alive"voltageonTR tubes in radar equipment,itmay
be necessary todisconnectmeter-protectiondiodesCR3andCR4.
Special .25Volt,1 Volt,and 5000 Volt Ranges
Note: Whenusingthe.25V and1 V jacks,theFunctionSwitch must be
settothe"+DC"position.Meterpolarity must beobservedby
applying thered test leadtothepositivecircuitpointandtheblack
test leadtothenegativecircuitpoint.
8.Tousethe.25volt range, settheRangeSwitchtothe".25"position,
andplugthered test leadintothe"+.25 V/50/*A" jack.
9.Tousethe1 volt range, settheRangeSwitchtothe"1.0V"position,
andplugthered test leadintothe"+1V"jack.
10. Tousethe5000volt range, settheRangeSwitchtothe5000V posi-
tion, andplugthered test leadintothe"DC5 KV" jack.

RCA Volt-Ohm-Milliammeter
Figure2.A-CVoltageMeasurement
AC Voltage Measurement (SeeFig.2.)
1.Setthe AC-DC Switchtothe "AC" position.
2. SettheRangeSwitchtoa positionconsiderablyhigherthanthe
voltagetobemeasured.
3.Plugtheblack test leadintothe "-COMMON" jackonthecontrol
panel,
4.Plugthered test leadintothe"+"jackonthecontrolpanelwhen
the2.5V,10V,50V,250V,or1000V range isused.Whenthe5000
V range isused,thered test lead must bepluggedintothe "AC5KV"
jack.
5.Connectthe test leads tothevoltagesource tobemeasured.
6.Reset theRangeSwitchtoa positionwhichgivesa suitablepointer
deflection.
7.ReadtheACvoltagefromthescalecorrespondingtothe range
selected.
8

RCA Volt-Ohm-Milliammeter
Figure3.D-CCurrentMeasurements
DC Current Measurement (SeeFig.3.)
1.Setthe AC-DC Switchtothe"+DC"or "—DC" positionasrequired.
2. SettheRangeSwitchtoa positionconsiderablyhigherthanthecur-
rent tobemeasured.
3.Plugtheblack test leadintothe "—COMMON" jackonthecontrol
panelforall ranges withtheexceptionofthe10 AMPS range.
4.Plugthered test leadintothe"+"jackonthecontrolpanelforall
ranges withtheexceptionofthe10Aand50/iA ranges.
5.Connectthe test leads in series withthecurrent flow tobemeasured.
6.ResettheRangeSwitchtoa positionwhichgivesa suitablepointer
deflection.
7.ReadtheDCcurrentfromthescalecorrespondingtothe range
selected.
8.Tousethe50/iA range, settheRangeSwitchtothe"50aA"position,
andtheFunctionSwitchto"+DC".Plugthered test leadintothe
"4-.25 V/50/*A" jack.Meterpolarity must beobservedbyapplyingthe
red test leadtothemostpositivecurrentconnectionandtheblacklead
tothenegativeconnection.
9.Tousethe10 AMP range plugtheblack test leadintothe "—10A" jack,
andthered test leadintothe"+10A"jack.Onthiscurrent range the
AC-DC Switch must besettothe "-f DC position,andtheRangeSwitch
settothe10Aposition.Meterpolarity must beobservedbyapplying
thered test leadtothemostpositivecircuitconnectionandtheblack
leadtothe other circuitconnection.

RCA Volt-Ohm-Milliammeter
Figure 4.DCOhmsMeasurement
Ohms Measurement ( SeeFig.4.)
1.SettheFunction Switch tothe"+DC"position.
2. SettheRange Switch totheappropriateposition.
3. Plug theblack test leadintothe "—COMMON" jackonthecontrol
panel.
4. Plug thered test leadintothe"+ " jackonthecontrolpanel.
5.Shortthe test leadstogetherandadjustthe ZEROOHMS control
until thepointerindicates"0" (full scale clockwise).
6.Connectthe test leadstotheresistancetobemeasured.
7.ResettheRange Switch ifnecessarytoa position which givesa suit-
ablepointerdeflection.Ifthisisnecessary, repeat steps 5 and6
beforeproceeding with step 8.
8.Readtheresistance from the OHMS scale,and multiply bytherange
factor.
CAUTION: Low-current,low-resistancedevices,suchasthermo-
couplesandmetermovements,maybedamagedunlessa rangeabove
"RXI" isused,becausethe WV-38A appliesupto1.5voltsacrossthe
resistanceundermeasurementwhentherangeselectorissetat"RX 1".
To facilitatecheckingthefront-to-backresistanceratioofelectrolytic
capacitorsandsemiconductordevices,the test leadpolaritycanbereversed
simply bysettingtheFunction Switch tothe "—DC" position.
10

RCA Volt-Ohm-Milliammeter
Figure5.DecibelMeasurement
AF Output (Decibel) Measurement (SeeFig.-5.)
1.SettheFunctionSwitchtothe "AC" position.
2. SettheRangeSwitchtoa positionconsiderablyhigherthanthe
decibel measurement tobe made.
3.Plugtheblack test leadintothe "—COMMON" jackonthecontrol
panel.
4.Plugthered test leadintothe "OUTPUT" jackonthecontrol
panel.
5.Connectthe test leads totheACsourcetobemeasured.
6.ResettheRangeSwitchtoa positionwhichgivesa suitablepointer
deflection.
7.Readthedecibel measurement directlyfromtheDBscalewhen
usingthe2.5V. range. Whenusingthe10V,50V,or250V range
refertothe chart locatedatthelowerrighthandcornerofthe
meter scale,forthedecibelfactor that must beaddedtothe meter
indication fortheproperdecibel measurement.

RCA Volt-Ohm-Milliammeter
Figure 6.WG-297HighVoltageProbe
AccessoryHigh-VoltageProbe
(Available on Separate Order)
The WG-297 High-VoltageProbe,incombination with a multiplier
resistor,asillustratedinFig,6,extendstheDCratingofthe WV-38A
toa maximumof50,000voltsforuseinhigh-impedancecircuits.The
WG-210 Multiplier Resistor, which hasa resistanceof900megohms,
multiplies the5000V.DC range bya factorof10times.(I.E.50,000V.
DC.) Similarly the WG-211A multiplierresistor, which hasa resistance
of 495megohms,multipliesthe250V.DC range bya factorof100
times.(I.E.25,000V.DC.)Theseprobesandmultipliercombinations
makepossible measurements inTVhigh-voltagepowersuppliesand
otherhigh-impedancecircuitshavinginherentlypoorregulation.
Applications
The WV-38A isdesignedto measure thesignificantcharacteristics
of electricalandelectroniccircuits.It will measure thevoltage,the
current,andtheresistanceofallDCcircuits.ForACcircuits,the
measurementisindicatedas R.M.S. voltsordecibels.Thedecibel
ranges arebasedona zero level of1 milliwatt in600ohms.Either part
of a mixedACandDCvoltagecanbemeasuredseparately with the
WV-38A. TheACvoltagecanbemeasured individually throughthe
useoftheoutputcircuit,andtheDCvoltagecanbemeasureddirectly
throughtheDCvoltagecircuit.

RCA Volt-Ohm-Milliammeter
Checking Capacitors
The R X 10,000 range ofthe WV-38A permitssomeindicationof
capacitorleakageresistance.A goodpaperor mica capacitorunder
1id will indicateabovethe20megohmmark ("2K") afterthe initial
surgerequiredtochargethecapacitoriscompleted.Iftheresistance
indicated islessthan20meg.,thecapacitorprobablyhasdefective
insulation. Thetimerequiredtochargethecapacitor will vary with
thecapacity.The greater thecapacity,themorethepointer will swing
andthelongerit will takeforittoreturnto infinity. Ifthecapacitor
is shorted,thepointer will notreturnto infinity. Ifthecapacitoris
open, there will beno initial pointerdeflection. Very small capacitors
will indicate only a slightdeflectionanda rapidreturnto infinity.
Electrolytic capacitors,however,normallyindicatesomeleakage,after
charging. Theamountofleakageisgenerallyrelatedtothecapacitance
andvoltagerating.Forexample,a lowvoltage,highcapacitanceunit
will indicatemoreleakage(lowerresistance)thana high-voltage,low
capacitanceunit.Whentestinganelectrolyticcapacitor,theredlead
mustbeconnectedtothepositiveandtheblackleadtothenegative
terminal ofthecapacitor,andthefunctionswitchonthe WV-38A
mustbeinthe"+DC"position.
Checking Rectifiers
The resistanceofcopperoxide,selenium, silicon andcrystalrecti-
fiers can bemeasuredinbothdirections.Theresistancemeasured
should bequitelargeinonedirectionandvery small intheopposite
direction. Thefront-to-backresistanceratiocanbecheckedeasilyby
settingtheFunction Switch from "+DC"to "—DC", thus reversingthe
polarity ofthe test leads.
Useofan Isolation Resistor
In certainsensitivecircuitsinradioandTVreceiversandother
I.F. orR.F.high-gainamplifiers,itisnotpossibletoconnectleads
without disturbingthenormaloperationofthecircuits. Usually, DC
voltage measurements insuchcircuitsrequirestheuseofa VTVM
with a resistor-isolationprobe,suchasanRCA VoltOhmyst. However,
when the VoltOhmyst isnotavailable,the WV-38A canbesub-
stituted,ifa resistorisusedinseries with theinstrument, clipped onto
theendoftheredprobe.Ifanexactmeasurementisnotrequired,almost
anyvalueofresistor,higherthanthe circuit impedence, will isolatethe
instrumentsoit will notoverlydisturbthe circuit. Whenanexact
measurementhastobemade,a resistorshouldbeused which exactly
multiplies theinputresistanceoftheinstrumentso that thereading
can bemadeononeofthehigherscales.The following tablegives
valuesofresistorstobeused:
Range ResistorReadingMultiplierScaletoRead
2.5V 50K 2 X 5 V
2.5V 150K 4 X 10V
50V 1 Meg.2 X 100V
250V 5 Meg.2 X 500V

RCA Volt-Ohm-Milliammeter
WV-38A VOM
Circuit Description
MeteringCircuit
The WV-38A meter circuit fortheAC Volts, DC Volts, andDCcur-
rentfunctionsconsistsofthecalibratingpotentiometerR22,connectedin
series with the 50/xA metermovement.
In theohmsfunction,thecalibratingpotentiometerisreplacedby
R25, thefrontpanel ZERO OHMS control.
Some modelsofthe WV-38A havetwospecial silicon diodes(CR3and
CR4) connectedacrossthemeterterminalstopreventdamagetothemeter
movementduetoaccidentaloverload.
DC Volts
The eight ranges oftheDCvolts circuit areobtainedbyaddingsuc-
cessively higher,valuesofresistorsinseries with themeter circuit.
The .25V rangeisconnecteddirectlytothemeter circuit. Thevoltage
divider networkusedfortheremaining ranges iscomposedofR27,Rl,R2,
R3, R4,R5,andR29.
AC Volts
The diodesCR1andCR2,along with R20andR21, form a full-wave
rectifier circuit, convertingtheACsignalinputtopulsatingDCvoltage.
The sixACvoltageranges,as with theDCvoltagesection,areob-
tainedbyusinga voltage-dividernetwork.Theresistors inthisnetworkare
RIO, Rll,R12,R13,R14,andR28.R24isa 6Kpotentiometerfor cali-
brating thelowACranges.R23,alsoa 6Kpotentiometer,isforcalibrating
thehighACranges.
DC Current
The DCcurrent ranges areobtainedbyswitchingtheappropriate
valuesofshuntresistanceacrossthemeter circuit tomaintain50/iA full-
scale deflection.The ranges andshuntingresistorsarelistedbelow:
RangeSeriesResistorsShuntingMeter
50/iA Noshuntused
1maR6,R7,R8,R9,andR26
10maR6,R7,R8,andR26
100maR7,R8,andR26
500maR8andR26
10AmpR26
Resistance
In resistancemeasurements,theohmscontrol,R-25,isconnectedin
series with themeter,andisusedforcalibratingor"zeroing"eachrange.
In theR x 1 andR x 100ranges,the1.5V"D" cell batteryisapplied
tothe circuit. IntheR x 10,000range,thefour1.5Vpenlightcellsarealso
used,resultingin7.5volts.Thebatteryvoltageisappliedtothemeter
circuit andshuntresistorsoftheparticularrangeso that whenthe test leads
areshorted, 50/*A ofcurrent pass throughthemeter,causingfull-scale
deflection.

RCA Volt-Ohm-Milliammeter
When a resistorisplacedacrossthe test leads,current flow through
themeter will bereducedinproportiontothevalueoftheresistor, thus
causing thepointertodeflectdown-scaletotheappropriatereading.
In theR x 1 range,R16andR17areinseries with themeter circuit,
and R19isshuntingthemeter circuit.
In theR x 100range,R17isconnectedinseries with themeter cir-
cuit, andR16andR19,connectedinseries,shuntthemeter circuit. R15is
in series with the1.5Vbattery.
In theR x 10,000range,R16,R17,andR19,connectedinseries,are
shunting themeter circuit. R18isconnectedinseries with thebatteries
(7.5V).
The 1 ampfuseisconnectedinseries with the —COMMON jack,and
servestoprotecttheresistors usedforohmsmeasurementagainstdamage
duetoaccidentaloverload.
Maintenance
The WV-38A mayberemoved from itscase simply byremovingfour
screws from therearofthecase.Themeter,panel,laminated circuit board
and batteriesareremovedasa completeunit.
The needforbatteryreplacementisindicatedwhentheinstrument will
notzeroproperlyontheOhmsranges. IfitisnotpossibletozerotheR X 1
and R X 100ranges,thelarge"D" cell requiresreplacement.Ifitisnot
possible tozerotheR X 10,000range,thefourpenlite cells requirereplace-
ment.Itisgenerallygoodpracticetoreplaceallbatterieswhena replacement
is needed.
The batteriesareinstalledintheinstrumentasshowninFigure7,
above.Itisimportant that thebatteriesareinstalled with thepolarityexactly
asshowninthe illustration, and that thebattery clips makepropercontact
with theterminals.

RCA Volt-Ohm-Milliammeter
Resistor Replacement
Almost alloftheresistorscontainedinthe WV-38A aremounted
on therearofthelaminated circuit board, which simplifies trouble-
shooting andrepair.Whenreplacinga resistor,thedefectiveresistor
should beremoved from thelaminated circuit boardandtheholesin
thelaminated circuit boardshouldbeopenedtoacceptthelead from
thenewresistor.Theholesmaybeopened with theuseofa toothpick
or appropriateprobe while thesolderismelted.Careshouldbetaken
topreventanyshort circuit toanyother part nearbywhenreplacingthe
resistor.
Fuse Replacement
The fusecontainedinthe WV-38A isusedtoprotecttheOhms-
Multiplier resistorsagainstburnoutduetoaccidentalmisuse(apply-
ing voltagetotheleadswhentheRange Switch isinthe"R XI" or
"R X 100"positions). This fusemaybereplacedbyunsolderingthe
lead tothe AC-DC Switch and clipping theotherlead.Thenewfuse
may besolderedontothelead clipped from thedefectivefuse.Care
should betakentopreventanyshort circuit, andifnecessary,a piece
of insulatingsleevingmaybeplacedoverthefusetopreventa short
circuit.
NOTE: A burnedoutfuse will maketheinstrumentinoperative
dn allfunctionsin which the 44—COMMON" jackisused.
DC Calibration
If anaccurateDCCurrentsource isavailable,itisrecommended that
thecalibrationpotentiometer,R-22,besetusingtheDCCurrentfunction
of the WV-38A, as follows:
1.SettheFunction Switch to "DC^ andtheRange Switch to"1MA."
2. Connectthe test leads from the "—COM" and"+"jackstoa 1 Ma
currentsource.
3. AdjustR-22so that themeterindicates1 MA(full-scaledeflection).
R-22 canalsobeadjustedusinga DCvoltagesource,asdescribed
below:
1.SettheFunction Switch to "DC" andtheRange Switch tothe"2.5V"
range.
2. Connectthe test leads from the "—COM" andjackstoa 2.5V DC
source.
3. AdjustR-22so that themeterindicates2.5V (full-scaledeflection).
NOTE: A fresh1.5V batterycanbeusedtocalibrateR-22onthe2.5V
range.Connectthe test leadstothebatteryterminals,andadjustR-22to
indicate 1.57volts(157onthe250scale).
16

RCA Volt-Ohm-Milliammeter
Rectifier Replacement
Therearetwosmallrectifierslocatedatthetopofthelaminated
circuit board.Ifeither,orbothrectifiersbecomedefective,the WV-38A
will giveincorrectindicationswhenmeasuringACvoltages.Whenre-
placing a rectifier,be sure toobservethepolarityofthedefective
rectifier beforeremoving.Thenewrectifiermustbereplacedinthe
properpolarity,andtheACvoltage ranges mustberecalibratedby
adjustingvariableresistors"R23"and "R24." TorecalibratetheAC
ranges ofthe WV-38A, proceedas follows:
AC Calibration
1.Setthe AC-DC Switchtothe "AC" position.
2. SettheRangeSwitchtothe"250V"position.
3. Connectthe test leadstoa knownACvoltagesourceof250V AC.
4.Adjustvariableresistor"R23" until the meter indicates full scale.
5.Removethe test leadsfromthe250voltACsource.
6.SettheRangeSwitchtothe"2.5V"position.
7.Connectthe test leadstoa knownACvoltagesourceof2.5V AC.
8.AdjustvariableResistor"R24" until the meter indicates full scale.
9. Removethe test leadsfromthe2.5V ACsource.
Removing the Laminated CircuitBoard
When itisnecessarytogain access totheunder-sideofthe
laminatedcircuitboardortothe parts locatedbetweenitandthe
frontpanel;thelaminatedcircuitboardmustberemoved.Toremove
thelaminatedcircuitboard,proceedas follows:
1.SettheRangeSwitchtothe"2.5V"position.
2. Removetheknobsfromthe AC-DC Switchandthe ZEROOHMS
control by pulling.
3. RemovetheknobfromtheRangeSwitchbylooseningtheset
screw.DONOTturnswitchfromitsposition.
4.Removethe three self-tappingscrewswhichholdthelaminated
circuit boardontothepanelposts.
5.Removethetwohex nuts andwashersfromthe meter studs.
6.Removelaminatedcircuitboard,observingcopperringsplaced
betweentheboardandthe meter. DONOTloseormisplace these
copperringsastheyfunctionasthecontactsfromthelaminated
circuit boardtothe meter. Whenreplacingtheboard,makecertain
that thecopperringsareplacedbetweenthelaminatedcircuit
boardandthe meter, otherwise,the WV-38Awill notfunction
properly. Also dress theinterconnectingleadsawayfromthe
"AP5KV" and DC5KV" eyeletsandresistors.

:RCA Volt-Ohm-Milliammeter
Replacement PartsList
WV-38A Volt-Ohm Milliammeter
When ordering replacement parts, include the stock number and description ofthe part, the
instrument type. Partswithoutstocknumbersarestandardcatalog items.
All partsshould be ordered from your local RCA distributor.
Symbol
No.
Description S^k
Resistors
45K Ohms 1% %W ...... 217743,
150KOhms 17c %W 56483-A"
800KOhms 1%y2W93843
4 Megohms 1%%W218881
15 Megohms 1%1W99317
22.5 Ohms 1%1W (blue). 218815
2.0 Ohms 1%1W (yellow). 218813
0.452 Ohms 1%1W (red). 218812
238 Ohms 1% %W218806
6200 Ohms 1%V2W236084
37500 Ohms 1%V2W218809
200KOhms 1% %W56733
1 Megohms 1%%W208022
3.75 Megohms 1%1W....218880
110 Ohms 1%%W237613
1138 Ohms 1% %W218807
21.85K 1%y2W218808
117.7K 1% y2W218810
11.5Ohms. 1%1W(green)218814
5K 1%%W209637
5K 1%%W209637
Variable 6000 Ohms 225351
Variable 10,000 Ohms ....219488
ShuntAssy. 10 AMP .....219489
15K Ohms \% %W97761
20 Megohms 1%2W218816
80 Megohms 1%2W ...... 218817
Meter
Meter 50 Microamperes in-
cludingplastic caseand
scale 218818
Capacitor
Capacitor 0.1 MFD400V
Symbol
No.
Description
Stock
No.
Rl
R2
R3
R4
R5
R6
R7
R8
R9
R10
Rll
R12
R13
R14
R15
R16
R17
R18
R19
R20
R21
R22,
R23,
R24
R25
R26
R27
R28
R29
Ml
CR1,
CR2
CR3,
CR4
Fl
Bl
B2
SI
S2
Rectifier
Crystal DiodeTypeIN87.
230099
Crystal Diode 230125
Fuse
FusePigtail 3AG1 AMP
250V 212492
Batteries
Type D 1.5V VS-036
Type A 1.5V VS-034
Switches
RangeSwitch 218877
Function Switch 218876
Miscellaneous
Panel—with eyelet
assembly 218994
Case—(less handle
assembly) 218993
Handle—(includingclips
and hardware) 219092
Printed circuitboard
(less parts) 219091
Batteryholder (U shaped
forpenlight cells)219179
PenlightBattery Clip
FlashlightBattery Clip^. . 219178
TestLeads
Red, withprobe 221711
Black 221712
Meter case, plastic,
front and rear 218995
Knob pointer 1 inch ...213831
Knob smallwithmark ..219486
Knob small no mark ...219487
Screw—Handle mtg219093
Clip—Lead Holder
(on handle) 219094
Probe—Red Probe
and Tip219107
CI
Informationfurnished by RCA is believed tobe accurate and reliable.However, no
responsibility is assumed by RCA foritsuse;norforany infringements ofpatents
or otherrights of thirdpartieswhich may resultfrom itsuse.Nolicense is granted
byimplication or otherwise under any patent or patent rights of RCA.
18

he
ck
i.
99
25
92
36
34
77
76
94
93
92
91
79
78
11
L2
)5
31
86
87
93
94
07
-COMMON
Ft
1 AMP.
1 Bt
1.5V
1000VOC
250VDC
50 VDC
10V DC
2.5V DC
+ 10A -10A
NOTES:-
1. S1 SWITCHPOSITIONS-MARKED ON SIADRAWING
R27
_ 15K
+iv DCQV\Ar
POSITION RANGE
1 1000V/5000V
2 250 V
3
50V (.25V, IV, 50JJA)
4 10V
5 2.5V
6 500 MA
7
100 MA
8
10MA (10A)
9 1 MA
10 R X 1
11 R X100
12 R X 10000
+ .25V/50JJA DCQ-
OUTPUT
o
AC5KV
O
DC 5KV
o
- ct
* .1 MFD
R28
> 20 MEG
2W
O
R29
SO MEG
2W
tOOOVAC
CR3
+/ M1\
50 jJA
CR4
H4-
. R22
)6K/
CAL
2.ALLSWITCHWAFERSSHOWNAS VIEWED FROM FRONT (SHAFT END OF SWITCH)
3. S1SHOWNINPOSITION#1
4.S2SHOWNINW+DCHPOSITION
5.SWITCH CONTACTS
SHORT ARROWSINDICATEWIPERCONNECTION
LONG ARROWSINDICATE CENTER RING CONNECTION.
6.ALLRESISTORS'/2 WATT, ±1% UNLESSOTHERWISE NOTED.
, R15
110 < R18
117.7 K
If)
ts
id
Schematic WV-38A
NOTE: In some instruments RIOis
7.5 K,andR22,R23and
R24 are4 K.

ItC/1
Printed in U.S.A.