Olympus BH-2 BHT User manual

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RevisionHistory
RevisionDescriptionDate
1InitialreleaseJune17,2014
2Correctederrorincircuittheory.Addedvendorinfo,lamp house
repairprocedure,andlightpresetcontrol/switchinformation.March17,2016
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Copyright©2014,2016CarlHunsinger
Allrightsreserved.Thisdocumentmaynotbereproducedordistributed,inwholeorin
part,foranycommercialpurposewithouttheexpresswrittenconsentoftheauthor.
Permissionisherebygrantedtodistributethispdfdocumentinitsentiretyforpersonal,
non‐commercialpurposesonly,providedthatthecontentsarenotmodifiedinanyway,
includingthecopyrightnoticescontainedherein.Thisdocumentmaybefreelydistributed
onWWW,FTP,orBBSsitesinaccordancewiththeserestrictions.

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OlympusBH‐2(BHT/BHTU)Electronics   Revision2    Page2of24
Introduction
Thisdocumentprovidesadetaileddescriptionoftheelectricalcircuitryofthe100/115VversionoftheOlympusBHTand
BHTUmicroscopes,whicharepartoftheBH‐2family.Theinformationcontainhereinisintendedtosupplementthe
informationpublishedintheOlympusResearchMicroscopeSeriesBH2(BHS)RepairManual,byprovidingadditional
circuitdetailsandacompletetheoryofoperation,aswellascorrectingerrorsthatwerefoundinthecircuitdiagram
publishedbyOlympus.Thisinformationwasobtainedbyperformingtear‐downinspectionsoffunctionalBHTU
microscopesconfiguredfor100/115Voperation.
SafetyWarningsandDisclaimers
Thecontentofthisdocumentisprovidedforinformationalpurposesonly,withnoexpressedorimpliedwarranties
whatsoever,including,butnotlimitedto,function,suitability,safety,accuracy,andcompletenessofinformation.
Repairingyourownmicroscopemayseemlikeahipandcoolthingtodothatwillmakeyoutheenvyofallofyour
friends,butbeingdeadwillnot.Potentiallylethalvoltagesarepresentinsidethesemicroscopes.Donotattempt
repairsortroubleshootingifyoulackthenecessaryskills,training,andconfidencetosafelyperformrepairsonline‐
poweredelectricalequipment.Ifyouchoosetoattemptrepairsortroubleshooting,dosoatyourownrisk.
OverviewofElectricalCircuitry
TheelectricalcircuitryoftheOlympusBHT/BHTUmicroscopesresidescompletelywithinthebaseofthemicroscope
stand.ACpowerisprovidedbyanACinletjackontheback,wherethelinecordconnects.Thereisapowerswitchon
thefronttoturntheilluminationonandoff,aswellasanintensitycontrolontheright‐handsidetovarythelamp
voltage.Thereisavoltageselectorswitchonthebottomofthebasetoallowoperationundernormalorlow‐line
conditions,andenclosedwithinthebaseareapowertransformer,abridgerectifier,amainprintedcircuitboard,anda
powertransistor.A6V/20Whalogenlampresidesinthelamphouseontherearofthestand.Laterstandshavealight
presetswitchandascrewdriver‐adjustablelightpresetcontrol,locatedjustabovetheintensityslider,toprovidepreset
lightingintensityforphotographicapplications.
TheBHT/BHTUelectronicsperformstwoindependent,yetrelatedfunctions,inresponsetoavariablecontrolsignal
fromtheintensitypotentiometer.Thefirstfunctionisintensitycontrolofthehalogenlamp.Toprovidethis,the
dimmercircuitryvariesthevoltageappliedtothelampinresponsetothiscontrolsignal.Thesecondfunctionisdisplay
ofthelampvoltageviaafour‐segmentLEDbar‐graphdisplay,whichalsooperatesoffoftheintensitycontrolsignal.
Detailsofbothofthesecircuitfunctionsaredescribedinthesectionsbelow.
LampDimmerCircuitry
Figure1isasimplifiedschematicdiagramofthelampdimmercircuitry.Thisdiagramcontainsthedetailsnecessaryfor
anunderstandingofthebasicoperationofthelampdimmer.Unnecessarydetailssuchassuchasswitching,fusing,
electricalinterconnects,andcurrentlimitinghavebeenomittedforclarity.RefertoAppendix2andAppendix3ofthis
documentforcompleteanddetailedschematicdiagramsoftheBHT/BHTUelectronics.
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Figure1–BHT/BHTULampDimmerCircuitry(withoutCurrentLimiting)

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OlympusBH‐2(BHT/BHTU)Electronics   Revision2    Page3of24
ElectricalpowerfromtheAClineisappliedtotheequipmentviatheAClinecord,whichplugsintoJ101onthebackof
themicroscopebase.PowertransformerT101convertstheAClinevoltage(120Vor240V,dependingonwhich
transformerisinstalled)toapproximately9VRMSonthesecondarywinding.Theoutputofthesecondarywinding
feedsintobridgerectifierDB101,whosefull‐wave‐rectifiedoutputinturnfeedsthelampdimmercircuitry.Bridge
rectifierDB101isnecessarytoprovideDCtothelampdimmercircuitry,sincetransistorsQ101andQ201inthedimmer
circuitarebipolarjunctiondeviceswhichcanconductcurrentinonlyasingledirection.
PotentiometerRV101controlsthelampintensity.WhenRV101isadjustedforminimumintensity(i.e.,thewiperisat
thetopendofitstravel),thefulloutputvoltageofbridgerectifierDB101isfedtothebaseoftransistorQ201via
resistorR202.Underthiscondition,transistorQ201willnotconductsincethebase‐emitterjunctionisnotforward
biasedandtherewillbenocollectorcurrentinQ201,andthereforenobasecurrentintransistorQ101.Withoutbase
current,transistorQ101willbecutoffandnocurrentwillflowthroughthelamp.
AspotentiometerRV101ismovedfromitsminimumintensitypositioninthedirectionofincreasingintensity(i.e.,the
wiperismovedtowardsthezeroreferenceground),thecontrolsignalfeedingthebaseoftransistorQ201decreases,
progressivelyforwardbiasingitsbase‐emitterjunctionandallowingittoincreasinglyconductcollectorcurrent.Since
thecollectorcurrentoftransistorQ201isthebasecurrentoftransistorQ101,Q101inturnbeginstoconductincreasing
amountsofcollectorcurrent,whichflowsthroughthehalogenlamp.Thelowertheamplitudeofthecontrolsignalfrom
thepotentiometer,thehighertheresultinglampcurrentandcorrespondinglampintensity.
TheoverallDCcurrentgainofthelampdimmerisconsiderable,andisapproximatelyequaltotheproductofthe
individualβvaluesoftransistorsQ201andQ101(i.e.,βOVERALL~βQ201xβQ101).BecauseofthishighvalueforβOVERALL,the
halogenlampwillbefullyilluminatedwithlittlebasecurrentintransistorQ201,therebyintroducingonlyaminimal
voltagedropacrossresistorR202.Neglectingthisminimaldrop,thevoltagepresentonthebottomterminalofthelamp
isapproximately0.7Vhigherthanthecontrolsignalfromthepotentiometer,atanysettingofthepotentiometer
(excludingtheminimum‐intensitysetting,wherethereisnoforwardbiasonthebase‐emitterjunctionoftransistor
Q201).Thismeansthatthelampvoltagemaybeadjustedfromzeroatoneextremeoftheintensitycontroltonearly
thefulloutputvoltageofDB101attheotherextremeoftheintensitycontrol.
Figure2isthelampdimmercircuitryshowninFigure1withtheadditionoftransistorQ202,resistorR201,andcapacitor
C202.Thesethreecomponentsprovideacurrent‐limitingfunctionforthedimmer,topreventdamagetothelampin
theeventofpowersurgesontheAClineandtominimizethermalstressesonthelampatpower‐up.
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Figure2–BHT/BHTULampDimmerCircuitry(withCurrentLimiting)

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OlympusBH‐2(BHT/BHTU)Electronics   Revision2    Page4of24
ResistorR201,thecurrent‐sensingresistor,iseffectivelyinserieswiththehalogenlamp.Solongasthelampcurrent
remainswithinthenormalrange,theresultingvoltagedropacrossresistorR201isinsufficienttoinitiateconductionof
transistorQ202,andthedimmeroperatesasdescribedintheparagraphsabove.However,ifforanyreasonthelamp
currentgetshighenoughthatthevoltagedropacrossresistorR201issufficienttoturnontransistorQ202,theresulting
collectorcurrentoftransistorQ202shuntsthebase‐emitterjunctionoftransistorQ201,reducingitsbasecurrentandin
turnreducingthelampcurrent.Thisnegative‐feedbackmechanismlimitsthepeaklampcurrenttoapproximately7.3A.
CapacitorC202provideslow‐passfilteringforthebaseoftransistorQ202,preventinganyhighfrequencynoiseorRF
fromaffectingthelampdimmer.
Figure21,Figure22,andFigure23showthevoltageandcurrentwaveformsofthehalogenlampwiththedimmer
operatingatthe100%,50%,and20%settingsoftheintensitycontrol,respectively.Figure24showsthedimmer
operatingundercurrent‐limitingconditionsatthe80%settingoftheintensitycontrolandwithanabnormallylowlamp
resistanceof0.2Ω.
LEDBar‐GraphDisplayCircuitry
Figure3isasimplifiedschematicdiagramoftheLEDbar‐graphdisplaycircuitry.Thisdiagramcontainsthedetails
necessaryforanunderstandingofthebasicoperationoftheLEDcircuitry.Unnecessarydetailssuchassuchas
switching,fusing,andelectricalinterconnectshavebeenomittedforclarity.RefertoAppendix2andAppendix3ofthis
documentforcompleteanddetailedschematicdiagramsoftheBHT/BHTUelectronics.
ThiscircuitsuccessivelyilluminatesthefourLEDsinthebar‐graphmoduleastheintensitycontrolismovedfromits
minimumsettingtoitsmaximumsetting.ThevariableoutputfromthewiperofpotentiometerRV101actsasthe
controlsignalfortheLEDdisplaycircuitry(aswellasforthedimmercircuitdescribedearlier),whichfeedsthenon‐
invertinginputsoffourop‐ampsusedascomparators.Thecontrolsignalisatmaximumamplitudeattheminimum
intensitysetting,andisatzeroamplitudeatthemaximumintensitysetting.Thefourcomparatorseachhavespecific
switchingthresholds,whichareconfiguredtoallowthecomparatorstoilluminatetheLEDsatfourpre‐definedlamp
voltagesof2V,4V,6V,and7V,inresponsetothedecreasingcontrolsignalfromtheintensitypotentiometer.
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Figure3–BHT/BHTULEDBar‐GraphDisplayCircuitry

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OlympusBH‐2(BHT/BHTU)Electronics   Revision2    Page5of24
FilteredDCPowerSupply
DiodeD201andcapacitorC201operateasapeakdetectortoproducefilteredDCpowerfromthefull‐wave‐rectified
outputofbridgerectifierDB101.ThisfilteredDCpowerlinesuppliespowertothecomparatorsandtheirrespective
LEDs.TheACripplepresentonthislinedependsontheamountofcurrentpulledbythecomparatorsandLEDs.At
minimalcommandedlampintensity(i.e.,withallfourLEDsintheoffstate),verylittlecurrentisrequiredandthevoltage
onthislineisapproximately+10.5VwithlittleACripple.Asthelampintensityisincreased(andtheLEDsbeginto
successivelyilluminate),thecurrentdrainonthislineincreasesasdoestheresultingACripple.Whenthelampisat
maximumintensity,allfourLEDsareilluminatedandtheACrippleisatitsmaximum,resultinginanaveragevoltageon
thefilteredDCpowersupplylineofapproximately+9.5V.Figure25showstheripplevoltageonthefilteredDCpower
supplylinewiththeequipmentoperatingunderworst‐caserippleconditionsofmaximumlampintensity.Thegreen
traceisthepositiveoutputofbridgerectifierDB101andthebluetraceisthefilteredDCpowersupplyline.
ComparatorThresholds
Theswitchingthresholdsofthefourop‐ampcomparatorsareprovidedbyafour‐stagevoltagedividerconsistingof
resistorsR208,R209,R210,R211,andR212.Thesethresholdsareconfiguredtoallowthecomparatorstoilluminatethe
LEDsatpre‐definedlampvoltagesof2V,4V,6V,and7V,inresponsetothedecreasingcontrolsignalfromtheintensity
potentiometer.Figure26showsthethresholdvoltagesontheinvertingpinsoftheop‐ampcomparators.Thegreen
traceisthepositiveoutputofbridgerectifierDB101,fromwhichthefourthresholdvoltagesarederived.Theblue,red,
cyan,andmagentatracesarethethresholdvoltagesontheinvertinginputsofIC1‐A,IC1‐D,IC1‐B,andIC1‐C,
respectively.
Control‐SignalClamp
ResistorsR213andR214,anddiodesD202,D203,andD204,clampthevoltageleveloftheintensitycontrolsignalfrom
potentiometerRV101tokeepthenon‐invertinginputsofthecomparatorsfromeverdroppingbelowapproximately
+0.7V.ThisisnecessarytopreventtheLEDsfromilluminatingbrieflyduringtheintervalswhereboththewiperof
potentiometerRV101andthecomparatorthresholdsdroptozeroatthezerocrossingsoftheACline.Ifbothinputsto
thecomparatorswereallowedtosimultaneouslydroptozero,thecomparatorswouldbeinanindeterminatestate,and
dependingontheinput‐offsetvoltageparametersofthespecificop‐ampdevices,theiroutputscouldpulllowduring
theseintervals,resultinginoneormoreLEDsnotfullyextinguishingwhentheyshould.
Theoperationofthecontrol‐signalclampisasfollows.ResistorR214feedsaDCcurrentthroughthetwoseries‐
connectedsilicondiodes,D203andD204,producingapotentialontheanodeofdiodeD204twodiodedropsabove
ground(approximately+1.4V).TheanodeofdiodeD202connectstothis+1.4Vnodeanditscathodeconnectstothe
non‐invertinginputsofthefourcomparators.ResistorR213couplesthecontrolsignalfrompotentiometerRV101tothe
non‐invertinginputsofthecomparators.AnytimethecontrolsignalislowenoughtoforwardbiasdiodeD202,the
voltageonthenon‐invertinginputsofthecomparatorsisclampedtoapproximately+0.7V(i.e.,onediodedroplessthan
+1.4V).AsthevoltageonthewiperofRV101increases,diodeD202turnsoffandiseffectivelyoutofthecircuit,thereby
providingnofurtherclampingaction.Thismechanismallowstheintensitycontrolsignaltoswingpositivewithout
restraint,butpreventsitfromdroppingbelowapproximately+0.7V.Figure27showsthewaveformoftheclamped
controlsignalatthe50%settingoftheintensitycontrol,asmeasuredatthenon‐invertinginputsofthecomparators.
VoltageComparators
IntegratedcircuitIC1isaNECuPC324Cquadoperationamplifier.AllfoursectionsofIC1areoperatedopen‐loopas
voltagecomparatorsandareconfiguredtodrivethefourbar‐graphLEDsinresponsetotheclampedcontrolsignalfrom
potentiometerRV101.EachcomparatorilluminatesitsassociatedLEDbydrivingitsoutputlowduringtheintervals
wheretheclampedcontrolsignaldropsbelowitsthresholdvoltage,andextinguishesitsLEDbydrivingitsoutputhigh
duringtheintervalswheretheclampedcontrolsignalexceedsitsthresholdvoltage.Figure28showstheoperationof
oneofthecomparators(IC1‐B)withthe6VLEDilluminated.Inthesewaveforms,theintensitycontrolissettothe70%
setting.ThegreenwaveformisthethresholdvoltagepresentontheinvertingpinofIC1‐B,andthebluewaveformisthe
clampedcontrolsignalonthenon‐invertingpinofIC1‐B.Duringtheintervalswherethecontrolsignalisbelowthe
thresholdvoltage,thecomparatoroutputpullslow,illuminatingthe6VLED,andduringtheintervalswherethecontrol
signalisclampedtoapproximately+0.7V(andisexceedingthethresholdvoltage),thecomparatoroutputpullshigh,


OlympusBH‐2(BHT/BHTU)Electronics   Revision2    Page6of24
extinguishingthe6VLED.Ifthesettingoftheintensitycontrolisdecreasedtothepointwheretheclampedcontrol
signalexceedsthethresholdwaveform,the6VLEDwillcompletelyextinguish.Theoperationoftheremainingthree
comparatorsissimilartothisone,differingonlyintheirthresholdvoltages.
PowerLED
ResistorR203andLED“A”functionasthepower‐onindicatorforthemicroscope.
ErrorsintheOlympusDocumentation
Inthecourseofresearchingthisdocument,twoerrorswereidentifiedintheschematicdiagrampublishedinthe
OlympusResearchMicroscopeSeriesBH2(BHS)RepairManual.BothoftheseerrorsareintheLEDbar‐graphdisplay
circuitry.
Bar‐GraphLEDs
Thefirsterrorisinthewiringofthefourbar‐graphLEDs,asshowninDetail1ofAppendix2andAppendix3ofthis
document.TheOlympusmanualshowstheseLEDswiredwiththeircathodesconnectingtotheirrespectivecomparator
outputsandwiththeiranodeswiredtotheirrespectivecurrent‐limitingresistors.Theactualcircuitconfiguration(as
observedonthemainboardsoffunctionalBHTUequipment)hastheanodesofthefourLEDsconnectedtothefiltered
DCpowersupplylineandthecathodesconnectedtotheirrespectivecurrent‐limitingresistors.Thisisaminor
discrepancyandeitherconfigurationwouldworkequallywell,buttheactualas‐builtconfigurationisshowninthis
document.
Control‐SignalClampingNetwork
Theseconderrorisinthewiringofthecontrol‐signalclampingnetwork,asshowninDetail2ofAppendix2and
Appendix3ofthisdocument.TheOlympusmanualshowsthisnetworkfedfromthefull‐wave‐rectifiedoutputofthe
bridgerectifier,butintheactualcircuitconfiguration(asobservedonthemainboardsoffunctionalBHTUequipment),
thisnetworkisfedfromthefilteredDCpowersupplyline.Thiserrorisofgreaterconsequencethanthefirst,asthe
circuitpublishedintheOlympusrepairmanualwouldnotguaranteethattheLEDsremainoffaroundthezerocrossings
oftheACline.
RemovingtheElectricalBasefromtheStand
TogainaccesstotheelectronicsinthebaseoftheBHT/BHTUstand,theelectricalbasemustberemovedfromthebase
ofthestand.Besuretotakesufficientnotesandplentyofphotographsbothbeforeandduringthedisassemblyprocess
tomakesurethateverythingcanbecorrectlyreassembledlateron.Beforeremovingtheelectricalbase,lookatthe
right‐handsideoftheunit,justabovetheintensityslider,andnotewhetherornotalightpresetcontrolandswitchare
present.Theearlierunitsdidnotincludethesecomponents,butthelateronesdid.
Next,removeallthemajorcomponentsfromthemicroscopestand(i.e.,ACpowercord,condenser,stage,eyepieces,
viewinghead,andobjectives).Doingsowillmakethestandeasiertomaneuverandwillpreventinadvertentdamageto
thesecomponentsduringdisassemblyandreassembly.Besuretoprotectthesecomponentsfromdustanddamage
whiletheyarenotinstalledonthestand.
Afterremovingthesecomponents,coverthetopofthearm(i.e.,thenosepieceturretandtheexposedmounting
dovetailfortheviewinghead)withacleanplasticbagandsecurethiswitharubberbandtokeepdustoutofthese
openings.ThisisespeciallyimportantonBHTUstandswhichhaveanopticalcorrectionlenslocatedjustbelowthe
viewingheadtocorrectforthedifferenceintubelengthintroducedwiththereversednosepiece.
Withthestandinitsnormaluprightposition,removethelamphousefromthebackofthebase.Thelamphousesimply
plugsintothebase,andcanberemovedbygraspingitandpullingitstraightback.Setthelamphouseasidetoprevent
damage.Donottouchthehalogenlampwithyourfingers,asoilsfromyourskinwillcauseprematurefailureofthe
bulb.Ifthebulbisaccidentallytouched,cleanitwithisopropylalcohol.
Carefullyturnthestandupsidedown,exercisingcautiontopreventimpactstothefocusknobsandtothe
condenser/stageholder.Usinga5/32”Allentool,removethefourhexsocket‐headcapscrewsfromthebottomofthe


OlympusBH‐2(BHT/BHTU)Electronics   Revision2    Page7of24
stand,asshowninFigure4.Holdtheelectricalbaseinplaceandsetthestandinitsnormaluprightpositiononaflat
surface,beingcarefulnottolettheelectricalbaseshiftasyoudoso.
Liftthestandfromtheelectricalbasebygraspingthearmandliftingstraightupuntilthebottomofthestandwellclears
theelectricalbase.Iftheunitcontainsalightpresetcontrolandswitch,besuretodisengagetheprintedcircuitboard
containingthepresetcontrolandswitchfromthenotchinthesideofthebasebeforeliftingthestandclearofthe
electricalbase.
Thestand,withouttheelectricalbase,maynowbeplacedonacleanflatsurfaceinitsnormaluprightposition.Withthe
electricalbaseremoved,thefragileilluminationcomponentsareexposedontheopenbottomofthestandandmaybe
damagedifthestandisnotplacedonasuitableclutter‐freesurface.Storethestandsomeplaceoutofharm’swayand
wheredustanddebriswillnotaccumulateontheexposedlightingcomponents.

Figure4–BottomViewofBHT/BHTUElectricalBase(100/115VVersion)
SettingUpforTroubleshootingtheBase
Settheelectricalbaseonasuitableworksurface.Iftheunitincludesalightpresetcontrol/switch,orienttheprinted
circuitboardcontainingthecontrolandswitchsuchthatitwillnotmakecontactwiththechassisoranyother
electricallyconductiveitemsduringthetroubleshootingprocess.
CarefullyplugthelamphouseintoJ103ontherearoftheelectricalbase,asshowninFigure5,makingsurebothcontact
pinsofthelamphouseengagethematingreceptaclesofJ103.Thelamphousewillbefragileandunsupportedwhen
pluggedintotheelectricalbasewithoutthestand,sincethetwoalignment/supportpinsonthelamphousewillnotbe
engagedwiththematingholesinthestand.Onceagain,donottouchthehalogenlampwithyourfingers.

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OlympusBH‐2(BHT/BHTU)Electronics   Revision2    Page8of24
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Figure5–LampHousePluggedintoJ103ofBHT/BHTUElectricalBase(100/115VVersion)
WiththeAClinecordunpluggedfromthewallreceptacleandwiththeACpowerswitchonthefrontoftheunitinthe
OFFposition,plugthelinecordintotheACinletjackontherearofthebase.Exerciseextremecautionfromthispoint
forward,aspotentiallylethallinevoltagewillbepresentatvariousexposedpointswithintheelectricalbase.Plugthe
AClinecordintoaproperlygroundedACreceptacle.Theelectronicsmaynowbeoperatedasnecessaryfor
troubleshootingpurposes.Neveroperatethemicroscopeifthechassisbondingscrewfortheground(center)pinof
theACinletjackislooseormissing,orifthewiretothislugiscutordamaged(seeFigure6).Thesearecriticalsafety
componentsandarenecessarytoensurethatthechassisofthemicroscopeisalwaysatasafepotentialintheeventof
anyelectricalfaultswithintheequipment.
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Figure6‐SafetyGroundConnectionforACInletJackofBHT/BHTUElectricalBase(100/115VVersion)

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OlympusBH‐2(BHT/BHTU)Electronics   Revision2    Page9of24
CommonProblemswiththeBHT/BHTUElectronics
TheelectronicsintheBHT/BHTUmicroscopeshaveproventoberemarkablyreliableovertheyears,butwithheavy
usage,failuresdooccur.Themostlikelyproblemsintheelectronicswillbebadorintermittentcontactsinthelamp
houseanderraticlampintensityduetodust,dirt,andoxidationwithintheintensitycontrol.
Wornoroxidizedcontactsinthesocketinthelamphousewillcausethehalogenbulbtonotilluminate,toflicker,orto
illuminateonlyintermittently.Ifareplacementlamphouseisnotavailable,thetroublesomelampsocketmaybe
replacedwithanewone,asdescribedlaterinthisdocument.Itmayalsobepossibletoeffectatemporaryrepairby
disassemblingtheexistinglampsocketandcleaningtheoxidizedcontactswithemerypaper,butthisshouldbeviewed
asatemporaryfixonly.
Dust,dirt,andoxidationwithintheintensitycontrolcancauseerraticlampintensityasthecontrolsliderismoved
throughoutitsadjustmentrange.Thiscanusuallybecorrectedbysprayingashortblastofvolumecontrol/contact
cleaner(afterunpluggingtheAClinecord)intotheintensitycontrolandmovingthesliderthroughoutitsfullrangeof
motionafewtimestodistributethecleaner(seeAppendix1ofthisdocumentforasuggestedcleaner).Exercisecaution
whensprayingthecleanerintothecontrolsoastominimizeoversprayandblow‐backontonearbycomponents.Be
suretoallowthecontactcleanersufficienttimetoevaporateoutofthecontrolbeforere‐applyingpowertothe
electricalbase.
ObtainingReplacementComponents
TheBHT/BHTUmicroscopesarenolongersupportedbyOlympus,andwithfewexceptions,factoryreplacementparts
arenotavailable.Someelectricalparts(orsuitablesubstitutes)areavailablefromthirdpartysources,andtheseparts
arelistedinAppendix1ofthisdocument,alongwithsourcesandpricing.
TheBHT/BHTUmicroscopeswereverypopularintheirday,andusedstandsandtheirvariousbitsandpiecesfrequently
showupforsaleonebay.Ifnecessary,replacementelectricalcomponentscanbesalvagedfromaspareelectricalbase.
Ifexactreplacementscannotbefound,makesurethatanysubstitutepartschosenforrepairshavesuitableelectrical
andmechanicalspecificationsandthattheyareinstalledinsuchawaythatitisnotpossiblefortheoperatortocontact
anylivevoltagepointswhileusingthemicroscope.
PowerTransformer
Thegoodnewshereisthatthepowertransformer(showninFigure7)rarelyfails.Thebadnewsisitmaybedifficultto
locateasuitablesubstituteforitifiteverdoesfail,duetotheuniqueformfactorwhichallowsittofitintothebaseof
theBHT/BHTUstand.Ifasuitablesubstitutecannotbefoundforthetransformer,thismaybeagoodtimetostarton
thatLEDconversionproject,whilelookingforanotherelectricalbase.
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Figure7–PowerTransformerMountedtoBHT/BHTUElectricalBase(100/115VVersion)

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OlympusBH‐2(BHT/BHTU)Electronics   Revision2    Page10of24
BridgeRectifier
ThebridgerectifierisanS15VB10(100V15A)chassis‐mountbridgerectifierwithpush‐onterminals(seeFigure8).Look
forasubstitutewithacontinuouscurrentratingof15AormoreandaPIVratingofatleast100V.Suitablesubstitutes
aretheNTE5322,KBPC1501,orKBPC1502.Besuretoinstallthereplacementwiththermalpastefillingtheinterface
betweenthepartandthechassis,tofacilitateheatflow.TheNTE5322isavailablefromAlliedElectronicsandfrom
Amazon.
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Figure8‐BridgeRectifierMountedtoBHT/BHTUElectricalBase(100/115VVersion)
LampIntensityControl
Thelampintensitycontrolisa500Ω slidingpotentiometer,withlineartaper,andwasmanufacturedbyNoble(see
Figure9).Ithas60mmoftravel,andthemountingholesarespaced65mmoncenter.Beforereplacingthispart,try
cleaningitwithvolumecontrol/contactcleaner(withpowerremovedfromtheequipment).Lookforasubstitutewitha
powerratingofatleast1/2W.
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Figure9–LampIntensityControlMountedtoBHT/BHTUElectricalBase(100/115VVersion)

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OlympusBH‐2(BHT/BHTU)Electronics   Revision2    Page11of24
LightPresetBoard
Thelightpresetboard,whichispresentonlaterstandsonly,containsasingle‐turn,500Ωlineartaperpotentiometerand
anSPDTrockerswitch(seeFigure10).WhentherockerswitchisintheOFFposition,theintensityslidepotentiometer
controlsthelightingintensity,andwhentheswitchisintheONposition,thescrewdriver‐adjustpotentiometercontrols
thelightingintensity.TheschematicforthelightpresetboardisincludedinAppendix3ofthisdocument.Asuitable
replacementforthepotentiometercouldlikelybefound,ifnecessary.However,therockerswitchismoreproblematic,
sinceitisthisswitchwhichsupportsthelightpresetboardinthechassis.Sincethisboardisnotnecessaryforbasic
operationoftheilluminationsystem,itmayberemovedandelectricallybypassedifsuitablereplacementpartscannot
befound,ortopermittheinstallationofanewerelectricalbaseintoanearlierstandthatdoesnothavethechassis
notchestoaccommodatethisboard.
RemovingandBypassingtheLightPresetBoard
RemovethelightpresetboardfromtheelectricalbasebyunpluggingthetwoconnectorsfromJ1andJ2onthecircuit
board.Next,cutthetwoconnectorsoffofthewires,makingthecutsasclosetotheconnectorshellsaspractical,in
ordertoleavesufficientwirelengthsfortheremainingsteps.Striptheendsofthetwoorangewiresthatwere
connectedtothefourpinconnectorandsolderthemtogether,insulatingwithheat‐shrinktubinginordertoprevent
shortingtothechassis.Dothesamethingforthetwobluewires(onewasconnectedtothetwo‐pinconnectorandthe
otherwasconnectedtothefour‐pinconnector)andthetworedwires(onewasconnectedtothetwo‐pinconnector
andtheotherwasconnectedtothefour‐pinconnector).Besuretoroutethesesplicedwiressuchthattheywillnotbe
pinchedandwillnotinterferewiththeopticalpathoftheilluminationsystemoncethestandisreassembled.
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Figure10–OlympusDV2288‐01LightPresetBoardonLaterBHT/BHTUElectricalBase(100/115VVersion)

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OlympusBH‐2(BHT/BHTU)Electronics   Revision2    Page12of24
ACPowerSwitch
TheACpowerswitch(seeFigure11)isanAlpsSDT‐7chassis‐mountDPSTrockerswitchwithaTV‐5ratingforUL/CSA.
Thisswitchcannotbecleanedwithcontrol/contactcleanersincetherearenoopeningstoinjectthecleaner.The
mountingholesofthisswitcharespaced34mmoncenter.

Figure11–ACPowerSwitchMountedtoBHT/BHTUElectricalBase(100/115VVersion)
VoltageSelectorSwitch
Thevoltageselectorswitch(seeFigure12)isachassis‐mountDPDTslideswitchratedfor4A/125VACand2A/250VAC.
Theslideprotrudes3/8”fromthemountingsurfaceandthemountingholesarespaced1‐1/8”oncenter.Thereare
openingsonbothendsofthisswitchthroughwhichcontrol/contactcleanermaybesprayedwhiletheslideris
positionedattheoppositeend(withpowerremovedfromtheequipment).Thelow‐voltagepositionofthisswitchis
rarelyneeded,andifacompatiblereplacementcannotbefound,theswitchcouldsimplybebypassedinorderto
hardwirethemicroscopetooperateatitsnominaloperatingvoltage.Sinceonlyonepoleonthisswitchisused,aSPDT
replacementcouldbeused.

Figure12–VoltageSelectorSwitchMountedtoBHT/BHTUElectricalBase(100/115VVersion)

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OlympusBH‐2(BHT/BHTU)Electronics   Revision2    Page13of24
MainBoard
AreplacementfortheUYPC48mainprintedcircuitboard(seeFigure13)israrelyneeded,sincethecircuitryonthis
boardisquitesimpleandcanusuallyberepairedwhennecessary.Suitablereplacementsformostcomponentscanbe
readilyfound.The5‐LEDmodulewouldbethehardestparttofind,butcouldbereplacedwithfiveseparaterectangular
LEDsifnecessary.TheuPC324Cop‐ampcanbereplacedwiththeLM324C,intheDIPpackage.TransistorsQ201and
Q202maybereplacedwith2N3906PNPdevices(besuretoaccountfordifferencesinpinoutwheninstallingtheseas
replacements).DiodeD201canbereplacedwitha1N4002or1N4004rectifierdiode,anddiodesD202,D203,andD204
canbereplacedwith1N916or1N4148small‐signaldiodes.The0.1Ω 5Wpowerresistor,R201,runsveryhotduring
normaloperation,andbecauseofthisthesolderjointscansometimesgobad.ResolderingtheleadsofR201maybe
enoughtofixaninoperativelampdimmer.ResistorR201canbereplacedwithaVishayCP0005R1000JE14part,
availablefromMouserElectronics.

Figure13–OlympusUYPC48MainBoardMountedtoBHT/BHTUElectricalBase(100/115VVersion)
Intherarecasethatthemainboardisdamagedbeyondrepair,anaftermarketreplacementfortheOlympusUYPC48
mainboardisavailablefromJ.C.RitcheyCompany,LLC(seeFigure14).Thisboard,whichisadrop‐inreplacementfor
theoriginalOlympusboard,comescompletewithareplacementpowertransistorandthenecessarytransistor
mountinginsulator.Nosolderingisrequiredforthisoptionifonlythecircuitboardneedstobereplaced,butsoldering
isrequiredifthepowertransistoristobereplacedatthesametime.Thislookstobeafaithfulreproductionofthe
originalOlympusboardandshouldperformwell.

Figure14–BHT/BHTUMainBoardReplacementKitfromJ.C.RitcheyCompany(photocourtesyJamesRitchey)

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OlympusBH‐2(BHT/BHTU)Electronics   Revision2    Page14of24
PowerTransistor
PowertransistorQ101isaToshiba2SD867NPNpowertransistorintheoldTO‐3metalpackage(seeFigure15).This
part,althoughobsolete,canstilloccasionallybefound,butexpecttopay$20ormoreforitwhenyoufindit.Ifthe
2SD867cannotbefound,thispartcanbereplacedwiththeSTMicroelectronicsBUX10part,whichisthesamepackage
styleandisalsoobsolete.TheNTE36partintheTO‐3PinsulatedcaseisagoodsubstitutethatisavailablefromAllied
ElectronicsandfromAmazon.
Whicheverapproachistaken,thereplacementtransistormustbeinstalledusingsuitablemountinghardwarewhich
provideselectricalisolationofthecollectortabfromtheequipmentchassis,andthermalpastemustbeusedonboth
sidesoftheinsulatortoenhancethermalconduction.Ifnoneofthepartslistedabovecanbefound,lookforanNPN
partwithacollectorcurrentratingofatleast15A,acollector‐to‐emittervoltageratingofatleast100V,andacurrent
gainofatleast40,inasuitablepowerpackage.

Figure15‐PowerTransistorMountedtoBHT/BHTUElectricalBase(100/115VVersion)
ACInletJack
Forsafety,alwaysreplacetheACinletjackwithanequivalentpart,whenavailable(seeFigure16).Makesurethatthe
chassis‐bondingscrewfortheground(middle)terminalofthejackispresentandsecureandthatthegroundingwireis
undamagedbeforeoperatingtheequipment.Thisconnectionkeepsthechassisatasafepotentialintheeventofany
electricalfaultswithintheequipment.
Ifasuitablereplacementjackcannotbelocated,afillerplatecouldbefabricatedtotaketheplaceoftheACinletjack,
withasuitableholedrilledtoallowanAClinecordtobeinstalledwithastrain‐reliefgrommet.Ifthisapproachis
chosen,besuretosecurelybondthegroundconductorofthepowercordtotheunitchassistomaintainequipment
safety.

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OlympusBH‐2(BHT/BHTU)Electronics   Revision2    Page15of24
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Figure16‐ACInletJackMountedtoBHT/BHTUElectricalBase(100/115VVersion)
LampHouse
ThereweretwostylesoflamphouseusedontheBHT/BHTUmicroscopes(seeFigure17).TheoriginalLS20‐Hversion
suppliedbyOlympus(aspartnumber5‐LB402)didnothaveametalreflectorbehindthebulb.Laterinthelifeofthe
BHT/BHTU,OlympusupgradedthelamphousetotheLS20H‐M2(partnumber5‐S119),whichincorporatedareflector
behindthelampinordertoprovidemoreusablelight.SincetheLS20H‐M2lamphouseisdirectlyinterchangeablewith
theearlierLS20‐Hpart,itshouldbeusedwheneverpossible.

Figure17–OriginalLampHouse(left)andNewerLampHousewithReflector(right)

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OlympusBH‐2(BHT/BHTU)Electronics   Revision2    Page16of24
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Figure18–LampHousePluggedintoBHT/BHTUElectricalBase(100/115VVersion)
ArepairkitfortheOlympuslamphouseisavailablefromJ.C.RitcheyCompany,LLC(seeFigure19).Thiskit,which
includesareplacementforthebackcoverandanewG4lampsocket,maybeusedtooverhauleithertheLS20Horthe
LS20H‐M2lamphouses.Thereplacementbackisprovidedsincetheoriginalcanbedamagedduringdisassembly.The
installationofthisrepairkitrequiressoldering,butdefectivelamphousesmaybesenttoJ.C.RitcheyCompanyforin‐
houserepair/exchange.

Figure19–BHT/BHTULampHouseRepairKitfromJ.C.RitcheyCompany(photocourtesyJamesRitchey)

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OlympusBH‐2(BHT/BHTU)Electronics   Revision2    Page17of24
LampHouseRepairProcedure1
AsanalternativetotheJ.C.Ritcheyrepairkit,aBenderandWirth990lampsocket(availablefromJ&HMicroscope
ServicesorfromBulbworks)maybeusedtoreplacetheexistinglampsocket.Toreplacethesocketwiththenew
Bender&Wirthpart,startbyremovingthehalogenlampandsettingitaside,beingcarefultonottouchtheglasswith
yourfingers.Next,removethelampreflector,ifpresent,byremovingthesmallscrewsecuringthereflectortothe
supportpost.Removethebackcoverbycarefullyheatingtheperimeterofthehousingwithaheatguntoloosenthe
adhesive,whilepushingfrominsidethehousing,behindthelampsocket,withascrewdrivertiptofreetheloosened
backpiece.Avoiddirectheatorpressuretotheventilationslotsonthebackcover,astheyarefragileandcanbe
damaged.Oncethebackcoverhasbeenremoved,cleanoffanyremainingadhesiveandremovethetwoscrews
securingtheoldlampsocketinplace.Unsolderthetwowirestofreetheoldsocketfromthehousing.Trimandstrip
thewiresonthenewsockettomatchthoseoftheoriginalsocket,andsolderthenewsocketinplace.Reinstallthetwo
screwstosecurethenewsocketinitsproperposition.Reinstallthebackcover,securingwithsuitableepoxy,and
reinstallthelampreflector(ifapplicable).Reinstallthehalogenlamp(betterstill,installanewlamp),beingcarefulto
nottouchtheglasswithyourfingers.Iftheglassisaccidentallytouched,cleanitwithisopropylalcoholbeforeuse.
HalogenLamp
TheBHT/BHTUstandusesaPhilips#7388halogenprojectorlampwithaclearquartzenvelopeandaG4base(seeFigure
20).Thislamp,whichhasacolortemperatureof3200K,acolorrenderingindexof100,andoutputs475lumens,is
ratedfor6V/20Wwithanadvertisedlifeof100hoursatfullbrightness.ThePhilips#7388maybepurchasedfrom
BulbworksorAmazon.Alternatively,anyofthemanufacturer’spartnumberslistedinTable1maybeusedfor
replacementsaswell.

Figure20–Philips#7388FHE/ESBT3HalogenProjectionLamp
ManufacturerPartNumber
Philips7388(256784)
Osram54261or64250HLX
UshioFHE/ESB(1000532)
GE778(49718)or788(943117)
Nikon79099
Olympus8‐C405
Reichert11143
SwiftMA‐780
Table1–SuitableHalogenLampsforOlympusBHT/BHTUMicroscopes


1LamphouserepairprocedurecourtesyJerryClementofJ&HMicroscopeService,Inc.

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OlympusBH‐2(BHT/BHTU)Electronics   Revision2    Page18of24
LampDimmerWaveforms
Allofthewaveformsinthefollowingfiguresareshownrelativetothenegativeoutputofthebridgerectifier,whichis
thezeroreferencepoint.Thesewaveformswereproducedusingversion4.19eoftheLTSpiceIVcircuitsimulator.

Figure21–LampWaveformsatMaximumIntensity(100%SettingofIntensityControl)



Figure22–LampWaveformsatMediumIntensity(50%SettingofIntensityControl)

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OlympusBH‐2(BHT/BHTU)Electronics   Revision2    Page19of24
LampDimmerWaveforms(continued)
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
Figure23–LampWaveformsatLowIntensity(20%SettingofIntensityControl)



Figure24‐LampWaveformsduringCurrentLimiting(80%SettingofIntensityControl,LampResistance0.2Ω)

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OlympusBH‐2(BHT/BHTU)Electronics   Revision2    Page20of24
LEDBar‐GraphDisplayWaveforms
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Figure25–FilteredDCPowerSupplyLineatMaximumLampIntensity(100%SettingofIntensityControl)



Figure26–Bar‐GraphComparatorThresholdVoltages