HUDSON 9
96
TELEVISION/MONITOR SAFFTY GUIDELINES FOR THE PROFESSIONAL SERVICE TECHNICIAN
SafetyChecks
Fireand ShockHazard
Implosion
X-radiation
Afterthe originalserviceproblem hasbeen corrected,acompletesafety check
shouldbe made.Besure tocheck overtheentire set,notjust theareas
whereyou haveworked.Some previousservicer mayhaveleft anunsafe
condition,whichcould beunknowinglypassed onto yourcustomer.Be sure
tocheck allofthe following:
1. Besure allcomponentsare positionedin suchaway astoavoid the
possibilityof adjacentcomponentshorts. Thisis especiallyimportant
onthose chassiswhichare transportedto andfromthe serviceshop.
2. Neverrelease arepairedunit unlessall protectivedevicessuch as
insulators,barries, covers,strainreliefs, andother hardwarehavebeen
installedin accordancewiththe originaldesign.
3. Solderingand wiringmustbe inspectedto locatepossiblecold solder
joints,soldersplashes,sharp solderpoints,frayed leads,pinched leads,
ordamaged insulation(including theac cord).Becertainto remove
loosesolder ballsandall otherloose foreignparticles.
4. Checkacross-the-line componentsandother componentsfor physical
evidenceof damageordeterioration andreplace ifnecessary.Follow
originallayout,lead length,anddress.
5. Noleador componentshould touchareceiving tubeora resistorrated
at1 wattormore. Leadtension aroundprotrudingmetal surfacesor
edgesmust beavoided.
6. Criticalcomponentshaving specialsafety characteristicsareidentified
withansbytheRef.No.inthepartslistandenclosedwithinabrokenline
*(where severalcriticalcomponents aregrouped inonearea) alongwith
thesafety symbolsonthe schematicdiagrams and/orexplodedviews.
7. Whenservicingany unit,always useaseparate isolationtransformer
forthe chassisFailureto usea separateisolationtransformer may
exposeyou topossibleshock hazard,and maycausedamage to
servicinginstruments.
8. Manyelectronicproducts usea polarizedacline cord(onewide pinon
theplug.) Defeatingthissafety featuremay createapotential hazardto
theservice andtheuser. Extensioncords whichdonot incorporatethe
polarizingfeature shouldneverbe used.
9. Afterreassembly oftheunit, alwaysperform anleakagetest orresistance
testfrom thelinecord toall exposedmetalparts ofthecabinet. Alsocheck
allmetal controlshafts(withknobs removed),antenna terminals,handles,
screws,etc. tobesure theunit maybesafety operatedwithoutdanger of
electricalshock.
*Broken line
1. Allpicture tubesusedin currentmodel receiversareequipped withan
integralimplosion system.Careshould alwaysbe used,andsafety
glassesworn,whenever handlinganypicture tube.Avoid scratchingor
otherwisedamaging thepicturetube duringinstallation.
2. Useonly replacementtubesspecified bythe manufacturer.
1. Besureprocedures andinstructions toallyour servicepersonnelcover
thesubject ofX-radiation.Potential sourcesof X-rays inTVreceivers are
thepicture tubeandthe highvoltage circuits.Thebasic precautionwhich
mustbe exercisedisto keepthe highvoltageat thefactoryrecommended
level.
2. Toavoidpossible exposureto X-radiationandelectrical shock,onlythe
manufacturer'sspecified anodeconnectorsmust beused.
3. Itisessential thatthe servicetechnicianhas anaccurateHV meter
availableat alltimes.The calibrationof thismetershould bechecked
periodicallyagainst areferencestandard.
4. WhentheHV circuitryis operatingproperlythere isnopossibility ofanx-
radiationproblem. Highvoltageshould alwaysbe keptatthe manufacturer's
ratedvalue-no higher-for optimumperformance. Everytimea colorsetis
serviced,the brightnessshouldbe runup anddownwhile monitoringthe
HVwith ameterto becertain thattheHV isregulatedcorrectly anddoes
notexceed thespecifiedvalue. Wesuggest thatyouand yourtechnicians
reviewtest proceduressothat HVand HVregulationare alwayscheckedas
astandard servicingprocedure,and thereason forthisprudent routineis
clearlyunderstood byeveryone.It isimportant tousean accurateand
reliableHV meter.Itis recommendedthat theHVrecorded oneach
customer'sinvoice, whichwilldemonstrate aproper concernforthe
customer'ssafety.
5. Whentroubleshootingand makingtest measurementsina receiverwith
aproblem ofexcessivehigh voltage,reduce thelinevoltage bymeansof
aVariac tobringthe HVinto acceptablelimitswhile troubleshooting.Do
notoperate thechassislonger thannecessary tolocatethe causeofthe
excessiveHV.
:
:
WARNING OFF
SERVICE NOTE
Before removing theCRT anode cap, turnthe unit andshort the HIGH VOLTAGE tothe CRT DAG ground.
The CRT DAGis not at chassisground.
6. Newpicturetubes arespecifically designedtowithstand higheroperathng
voltages withoutcreating undesirableX-radiation.It isstrongly
recommendedthat anyshoptest fixturewhich istobe usedwiththe new
highervoltage chassisbeequipped withone ofthenew typetubes
designedfor thisservice.Addition ofa permanently connected HVmeter
tothe shoptestfixture isadvisable. TheCRTtypes usedin thesenew
setsshould neverbereplaced withany othertypes,as thismayresult in
excessiveX-radiation.
7. Itisessential touse thespecifiedpicture tubetoavoid apossibleX-diation
problem.
8. MostTVreceivers containsome typeofemergency "HoldDown"circuit to
preventHV from risingtoexcessive levelsin thepresenceof afailure
mode.These variouscircuits shouldbe understoodby alltechnicians
servicingthem, especiallysincemany hold down circuitsare inoperative
aslong asthereceiver performsnormally.
1. Unplugtheac linecord andconnecta jumperbetweenthe twoprongsof
theplug.
2. Turnonthe powerswitch.
3. Measuretheresistance valuebetween thejumperedac plugandall
exposedcabinet partsofthe receiver,such asscrewheads, antennas,
andcontrol shafts.Whenthe exposedmetallic parthasa returnpathto
thechassis, thereadingshould bebetween 1megohmand 5.2megohms.
Whenthe exposedmetaldoes nothave areturnpath to the chassis,the
readingmust beinfinity.Remove thejumper fromtheac linecord.
1. Donotuse anisolation transformerforthis test.Plugthe completely
reassembledreceiver directlyintothe acoutlet.
2. Connecta1.5k, 10wresistor paralleledbya 0.15uf.capacitorbetween
eachexposed metalliccabinetpart anda goodearthground suchasa
waterpipe, asshownabove.
3. Useanac voltmeterwith atleast5000 ohmsvoltsensitivity tomeasure
thepotential across theresistor.
4. Thepotentialat anypoint shouldnotexceed 0.75volts.A leakagecurrent
testermay be usedtomake thistest; leakagecurrentmust notexceed
0.5milliamps. Ifameasurement isoutside ofthespecified limits,thereis
apossibility ofshockhazard. The receivershould berepairedand
recheckedbefore returningitto thecustomer.
5. Repeattheabove procedurewith theacplug reversed.(Note:An ac
adapteris necessary whenapolarized plugis used.Donot defeat the
polarizingfeature oftheplug.)
Theprimary sourceofX-radiation inthis televisionreceiveris thepicture
tube.The picturetubeutilized inthis chassisisspecially constructedtolimit
X-radiationemissions. ForcontinuedX-radiation protection,the replacement
tubemust bethesame typeas theoriginal,including suffixletter,or aPhilips
approvedtype.
Manyelectrical andmechanicalparts inPhilips televisionsetshave special
safetyrelated characteristics.Thesecharacteristics areoften notevidentfrom
visualinspection norcanthe protectionafforded bythemnecessarily be
obtainedby usingreplacementcomponents ratedfor highervoltage,wattage,
etc.The useofa substitutepart whichdoesnot havethesame safety
characteristicsas thePhilipsrecommended replacementpart showninthis
servicemanual maycreateshock, fire,or otherhazards
LeakageCurrent ColdCheck
LeakageCurrent HotCheck
PictureTubeReplacement
PartsReplacement
1500 ohm, 10W
0.15 uF
WATER
PIPE
EARTH
GROUND
TO
INSTRUMENTS
EXPOSED
METAL PARTS
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