Sinclair ZX81 User manual

IMPORTANT:
Readthroughthe
instructionsbeforeyou
startassembly.
Ifanythingseemsunclearordifficult,contactusforadvicebefore
goingahead.
1.PREPARATION
Youwillneeda clean,dryandwelllitworkspaceinwhichtoassembleyourkit.Ifpossible,trytofind
somewherewherethepartscanstayundisturbedincaseyoudonotfinishthekitallatonce.Itisa
goodideainanycasetosplittheworkup- sayassemblethecircuitboardoneeueninn_tben.tffstjt.and
putthecasetogetherthenexteveningYouwillneedthesetools
(a)A lightelectricsolderingiron,say15to25wattswitha finetip
{b}Finegaugesolderwithresinfluxcore;NOTacidflux.
(c)A pairofsharpsidecutters.
(d)A 'Pozidriv'screwdriverwitha No.1 point.
(e)A mediumsizeordinaryscrewdriverand/ora 4BA spanner.
Thefollowingitemsareoptional,butuseful-
(a)A magnifyingglassforexaminingsolderjointsandlookingforshortcircuits,
(b)Somedesoldenngbraidorothersolderremovingtool.Betterstill,takecarethatyouputthe
componentsinrightthefirsttime- removingthemcanbeverydifficult.
(c)A pieceoffoamisusefultostopcomponentsfallingoutwhenyouturntheboardovertosolder
them
2.PRECAUTIONS
Therearenotmanyintegratedcircuits(IC s)inthekit,buttheyareallfairlyexpensiveitemsandmost
ofthemaresusceptibletodamagefromstaticelectricity.Thereisnocauseforworryifa few
precautionsaretaken:-
(a)Usethesocketssuppliedwiththekit-neversoldertheI.C.sdirecttotheboard- andkeepthe
I.C.sintheirprotectivepackinguntilyouarereadytoplugthemin.
(b)Neverinsertorremovethe! C s ordoanysolderingwithpowerappliedtothecomputer.
(c)Usea solderingironwitha properlyearthedbit.
<d)Carpetsandclothingofman-madefibres,andsyntheticsolesonshoes,arepronetobuildingupa
staticcharge.Earthyourselfbytouchinga largeobject,preferablymetallic,priortotouchingtheI.C.sIf
youdogeta shock,trychangingyourclothesorgoingbarefoot(seriously'}
3.COMPONENTEDENTIFICATION
Beforeyoustartassembly,checkthecomponentsagainstthecomponentlist(section8)andmake
sureyouknowwhateachpartis.Wehavetriedtocoveralldifferentmarkingsofthecomponents,but
variationsarepossible.
Noteinparticularthatthecomputer'smemorymaybesuppliedeitherastwo18pinI.C.s(IC4a& IC4b)
orasone24pindevice(IC4),andthatassemblyisnecessarilydifferentforeachversion.
Somecomponentsneedtogoinoneparticularwayround-
(a)TheI C s haveoneendidentifiedbya notch,and/ora spotordimpfenexttopin1 (Seefig.1)Note
thatallthe! C s facethesamewayontheboard,i.e.withtheirnotchestowardstheedgeconnector.
1

AlthoughtheI C.socketsdonotneedtogoanyparticularwayround,youmayliketoputthebevelled
corneratthenotchendoftheI.C.positionasa reminder,sincethesemicircieprintedontheboardwill
becoveredbythesocketinsomecases.
(b)Thediodes(prefixD)havetheir+ endidentifiedbythebandpaintedonthebody- orinthecaseof
componentswithseveralbands,the+ endwillbethewidestband.Thiscorrespondstotheflatbarof
thesymbolprintedontheboard.(Seefig.2).
(c)Theelectrolyticcapacitors(C3& C5}willhavea + or- symbolprintedonthem,andthe+ wireis
usuallylonger.(Seefig.3).
(d)Thetransistors(prefixTR)gointheboardasshownbythepictureprintedattheirpositions- i.e.
withtheirroundedcornersfacingtheedgeconnector.
(e)Thejacksocketsandmodulatorneedtohavetheirbusinessends(i.e.wherethepluggoesin)
facingoutwards,awayfromthecomponents.Thisshouldbeobviousbyinspectionoftheboardand
case.
(f)Theregulator(REG)andheatsinkneedtogoina particularwayround-justfollowfig.4.
(g)ThekeyboardconnectorsKB1& KB2havetheirpinsoffsetfromtheircentreline,andKB1goes
theoppositewayroundtoKB2.Makesurethatineachcasethebodyoftheconnectorcoversupthe
componentnumberontheboard.(Seefig.5).. , . ........-,.... ,.. ..
(h) The resistorpacks (prefix RP) have a 'common'
end markedwltn a whlte dot Thlssnould
9°attne
endmarkedwitha 'C'ontheboard.
(i)Thesingleresistors,therestofthecapacitors,andthefilterX1maybeputineitherwayround.

4.CIRCUITBOARDASSEMBLY
Thecircuitboardwillbesuppliedwithonesideprintedwithallthecomponentlocations- thisisthe
sidethecomponentsgo.Thisprintingisreproducedasfig.6 (Seereversesideofsheet)sincesomeof
themarkingswillbecoveredbycomponents.Allsolderingisdoneontheothersidewhichiscoated
witha greensolderresist- thiskeepsthesolderawayfromwhereitisnotneeded.Theexceptionis
theedgeconnectorareawhichshouldbekeptfreeofsoldertoensurereliableconnectiontotheRAM
packorprinteriftheyareused,Wesuggestyouassemblethecomponentsinthefollowingorder,
althoughitisnotcompulsory-
(i)Resistors,capacitorsand1Csockets- donotplugtheI C.sinyet.
(ii)Thediodesandtransistors.
(iii)The'large'components:thesockets,keyboardconnectors,modulator,theregulatorand
heatsink.
(iv)Finallyplugthe! C s intotheirsockets.
Thegeneralprocedureforeachcomponent:-
(a)Identifythepartanditspositionontheboardandinsertitintotheappropriateholes,bendingthe
leadsifnecessary.(Butseelater).Inthecaseofcomponentswitha numberofpins,makesurethat
theyhaveallgonethroughtheirholes.
(b)Holdthepartinposition- ifyoubenditsleadstodothis,donotpressthemfiatontotheboardas
thiswillmakethemdifficulttocutandwillencourageshortcircuits.
{c)Solderallthewiresonthe'greenside'oftheboardand,iftheyarelong,trimthemwiththeside
cutters.Noleadshouldstickoutmorethanabout3mmorV^'fromthesolderside.
Somecomponentsneedmoredetailedexplanation:-
(a)Thecapacitorsarerepresentedbya capacitorsymbolontheboard,ratherthana boxastherestof
thecomponentsare.Fig,7 explainshowtheyfitintheboardrelativetothesymbol.
(b)TherearefouroblongboxeslabelledR7-R10,R11-R14,R18-R22andR23-R26.Theseallcontaina
rowofresistorsstanding'onend'asinfig.8.Takecarewhenmountingthese:thelengthofbarewire
upthesideshouldnotbeallowedtoshortagainstanythingelse
(c)IC2andIC4havetwodifferentsizedboxesprintedontheboard1useonlytheholescorresponding
tothesmallerbox.
(d)Aspreviouslymentioned,IC4maybeineitheroneortwopackages,Onlytheappropriate1C
socketswillbesupplied,somakeabsolutelysureyouknowwhichversionyouhavegotbefore
proceeding.
IMPORTANT:-Ifyouhavethe24pin4118inyourkit,a shortwirelinkshouldbeinsertedintheholes
atpositionL1Usea componentleadoff-cutforthis.DONOTdothisifyouhavetwo18pin2114s,and
donotputanythinginpositionL2.
(e)Whenmountingtheregulator,donotbenditsleadstooclosetotheplastic.Boltitdownfirmlywith
itsheatsinkbefore soldering.
(f)Putthemodulator'swiresthroughtheholesmarked"Fr/UK1"and"UK2"Puteachleadthrough
theholeitisnearestto:donotcrossthemoverDonottrytobendthethickpinsonthemodulator:
holditinplacebyhandwhilstsoldering.Theblackcardtrimisa pushfitovertheaerialsocket.
(g)TheI.C.swillhavetheirpinssplayedoutslightlyandyoumayneedtopushtheminwardsslightly,
e.g.bypressingagainsta flatsurface,beforetheywillfitthesockets.Makesurethateachpinhasin
factgoneintoitsrespectivesocketandthatnonearecurledupundertheI C.
3

5.TESTING
Thecompletedboardshouldnowbecheckedvery thoroughlyforstrayblobsofsolder,dryjoints,leads
nottrimmed,etc.Alsomakedoublysurethatallcomponentsareintherightplaceandtherightway
round,andthatthe"standup"resistorsarenottouchinganythingelse.Ifeverythingseemsinorder,
theboardmaybetestedbeforeyouputitinthecase.Restthecompletedassemblyonaninsulating
surface(eg theseinstructions)makingsuretherearenowireoffcutsorsimilartrappedunderneath.
Thekeyboard's"tails"maynowbepluggedcarefullyintotheirconnectors:theonewith5 stripesgoes
intoKB1,theonewith8 stripesgoesintoKB2These"tails"arequitefragile,sohandlethemgently.
Thekeyboarditselfshouldsit(therightwayup)justinfrontofthecircuitboard-Donot removethe
backingpaperfromthekeyboardatthispoint.
YoumaynowconnectthecomputertotheT.V.andpowersupplyandtryitout-seethemain
instructionmanualfordetails
Onceyouaresurethecomputerisworkingcorrectly,putitinitscase- seesection7.Donotstrainthe
keyboardconnectionsunnecessarilybyusingituncased.
6.FAULTFINDING
ExperiencewiththeZX80hasrevealedthatthemajorityoffaultsonkitsareduetobadsoldering.Ifyour
computerdoesnotwork,switchitoffandCHECKITAGAIN.Ifyoufinda badjointorshort,shameon
youi Youshouldhavecheckedmorecloselythefirsttime.Ifyouaresurethefaultisinthecircuitry,try
thesetests--
(a)If thecomputerdoesnotworkat all,leaveit on fora coupleof minutesandfeeltheregulator- it
shouldbegettingwarm.Ifnot,checkthepowersupply,andthattheplugisintherightsocket(theone
nearestthekeyboard).Otherwise,lookattheconnectiontotheT.V.andmakesureitistunedin
properly-trybetweenchannels33and39UHF.
(b)Ifthecomputerworksandthengoesoff,andtheregulatorgetsveryhot,itisn'tboltedtothe
heatsinkproperly.
(c)Ifthecursorappearsonthescreen,butthekeyboardwillnotenter,checkfirstlythatthekeyboard
"tails"areproperlyintheirconnectors,andnottwistedinanywayAlsomakecertainthatthediodes
andthekeyboardconnectorsarealltherightwayround.
(d)Ifthescreengoesclearbutthereisnota cursor,trydisconnectingthepowersupplyandwaitinga
fewsecondsbeforetryingagain.
(e)Ifhorizontalblackandwhitestripespassthroughthepicture,suspectthepowersupply.Ifyouare
usingyourownsupply,itmayneedtobebettersmoothed(ifthecomputerisotherwiseworking)orof
aslightlyhigheroutput.Seethepowersupplyspecification(section9).
7CASEASSEMBLY
(i)Takethecasetop- thepartwiththeraised"Sinclair"logoand"ZX81"printedonit- andfeed
the"tails"ofthekeyboardthroughtheslotatthetoprighthandcornerofthekeyboardrecess.Donot
removethebackingpaperformthekeyboardyet,justlocateitintherecess:seefig.9.Holdthe
keyboardtemporarilyinplacewitha rubberbandora littlestickytape.
(ii)Holdthecircuitboardasinfig.10withthekeyboardconnectorsnexttotheslotwiththe"tails"
pokingthrough,Plugthe"tails"intotheirrespectiveconnectorsasshowninthediagram,andturnthe
boardoversothatthecomponentsfaceintothecasetopbehindthekeyboard.
NOTE.Specialattentionmustbemadetoensurethatthecorrectlengthofscrewisusedinthecorrect
hole.Theshortscrewsareyellowincolour,thelongscrewsareblackincolour.Fig,11showswhere
4

theselocateSeriousdamagewillresultifthelongscrewsareinsertedinthewrongholes.
(iii)Locatetheboardonthepillarsinthecase,makesurethejacksocketsarebehindtheholesinthe
side,andscrewitintothecase.Onlytwoholesneedscrewsinthematthispoint - Fig.11tellsyou
whichtwo;theothersareforthecasebottomfixing.Sincethescrewswillhavetoformtheirown
threadsintheplastic,theymaybea bitstifftoturnthefirsttimethereforeitisessentialthattheproper
screwdrivershouldbeused.Anordinaryflatscrewdriverwillalmostcertainlyslip,andmaycause
damagetothecircuitrywhenitdoes.Seethelistoftoolsgiveninsection1
(iv)Turnthecasetherightwayupagain,peeltheprotectivepaperoffthebackofthekeyboardandstick
itintoitsrecessinthemoulding(thekeyboardisselfadhesive- noextraglueisnecessary).Itwouldbe
aswelltopositionthe'keyboardcorrectlythefirsttime,toavoiddamagingitbycontinualrelocating.
Locatethetopedgeofthekeyboardagainstthetopedgeoftherecess,andstickitdowncarefully,
workinggraduallytowardstheloweredge.Havea dryrunfirstifyouareinanydoubt.Donottrytostick
thewholesurfacedowninonego.
(v)Aftercheckingthatthekeyboardconnectionsarestillsecurelyinplace,locatethebottomhalfofthe
caseandscrewittothetopwiththeremainingfivescrews.Finallytherubberfeetplugintofourofthe
recesses,overthescrewheads.Fig.11showsthelocationofscrewsandfeet.
(vi)Givethecomputera finalcheck,andstartusingit....
8.COMPONENTLIST
Notethatsomecomponentsaremarkedonthecircuitboard,butshownas"notused"inthislist.Do
notputanythinginthesepositions.
(a)Resistors.
Allresistorshavefourcolourbands:thefourthmaybegoldorsilver.
No.ValueMarkingsComments
R110KBrownBlackOrange
R2680Q BlueGreyBrown
R3Notused
R418KBrownGreyOrange
R5330Q OrangeOrangeBrown
R62K2RedRedRed
R7470Q YellowPurpleBrown
R8470Q
R9470Q
5

R10470Q
R11470Q
R12470fi
R13470£2
R14470£2
R15220KRedRedYellow
R16IKBrownBlackRed
R171K
R181K
R191K
R201K
R211K
R22K
R<"IK
R24IK
R251K
R261K
R271K
R28680QBlueGreyBrown
R291MBrownBlackGreenFourthbandmaybeyellow
R30Notused
R31Notused
R32Notused
R334K7YellowPurpleRed
R34220QRedRedBrown
(b)ResistorPacks
No.ValueMarkingsComments
RP18 x 10K10KQ9 leads'
RP2Notused
RP35 x 10K10KQ6 leads
(c)Capacitors
No.ValuesMarkingsComments
C147pF47Ceramicdisc
C247nF473Z
C322uF22H Electrolytic16Vmm
C447nF473Z Ceramicdisc
C51uF1[iElectrolytic5Vmin.
C6100pF100,101,nlOCeramicdisc
C747pF47
C847nF473Z
C947nF473Z
CIOlOnFlOn,103
Cll47nF473Z
C1247pF47
(d)Semiconductors
No.TypeComment
IC1Sinclair
Logic1C40pins158printedunderside
!C2236424pins
IC3Z80AorD780C-140pins
IC4MK411824pins
or
IC4auPD2114LC
orasIC4b18pins
6

!C4buPD2114LC-118pins
REG78055 Voltregulator
TR1ZTX313
TR2ZTX313
D1-D8* 1N4448Colours:Yellow,yellow,yellow,grey
or1N4148Yellow,brown,yellow,grey
or1S442 Yellowbands
Somediodesmayhavetheirnumberprintedontheminstead.
D9Notused
X1CDA6 BMC3 leadceramicfilter
(e)Othercomponents
ModulatortypeUM1233
3off3 5rnmjacksocketsforpower,earandmic.
2eff40pin1Csockets
Eitae"r. 2 off24pin1C sqckeis. „ . . .
or• T off24pinandZ off18pin|Csockets
KB15:\waykeyboardconnector
KB28~Waykeyboardconnector
Modulatortrim(blackcard)
Readymadeflatkeyboard
Aluminiumheatsink
4BAnut,boltandwasherforfixingregulatorandheatsink
Printedcircuitboard
2Casehalves
4Rubberfeet
7SelftappingPozidrivscrews- 3 Black(long),4 Yellow(short)
9.POWERSUPPLY
IfyouwishtouseyourownpowersupplywiththeZX81,itshouldconformtothesespecifications-
D.C. only -positivetothetipofthe3.5mmjackplug.Neednotberegulated,butshouldbewell
smoothed.
Voltage- between12voltsmaximumandabout8 voltsminimum(dependingonsmoothing)whenon
load.
Current- notlessthan600mA,or1 2Aoftheprinteristoworkfromthesamesupply.
10.SERVICE
WewillrepairyourcompletedZX81kitforafixedfeeof£1000Wecannotassembleyourkitforyou,
norcanwestartworkuntilthefeeisreceived.Inexceptionalcases,sayifthet.C.shavebeen
damagedbybeingputinthewrongwayround,wemayaskforanadditionalpayment.
Ontheotherhand,ifthetroublewasduetofaultycomponentssuppliedbyuswewillreiui.jthefull
servicefee.Westronglyadvise you,therefore,tobeverycertainthatyouhavecheckedthecomputer
thoroughly \oi mistakesbeforereturningit:seealsothehintsinsection6.
IfyoudoreturnyourZX81,packitwellandenclosea notegivingyournameandaddress,and
explainingthesymptomsofthetroubleandanytestsyoumayhavedone.Pleasereturntothis
address:
SinclairResearchServiceDept.
ChestertonMill
French'sRoad
Cambridge
CB43NP
®SinclairResearchLimited1981

COMPGIli£ITS& ACCESSORIES
i'OFTKSSUGGESTEDAPPLICATIONSFORUSERFORT
f
74162Sp' HID507(SingleDigitDisplay)11Op
74LS4740p16pinDILHeaderPlug60p
OA91diode9p16pinHeaderwith24"Cable
Openended180p
0.2" LEDRED13pLow current Solid State Buzzer lOOp
0.2" LED GREEN 15p6 Volt Relay (Singlepolechange-
over) contact rating 1A 120V AC/241K I60p
MountingClipforSinglepolepushbutton' 15p
RoundLedJp
»
Rectangular Led Loud Speaker 64R- 80R 80pu (
(T.edYelloworGreen)30p^
MountingClip7p

INCREMENTALSERIESPLUG& SOCKETSWITCHSETTINGSAPPENDIXB
GeneralITotes:
ITotethepositionsoftheplug—and-socketswitches(seeAppendixA)andthenumberingof
thepossiblepositionsofthe5 connectorplugs.Fivedistinctrangesofpositions
correspondtodifferentselectionfunctionsdescribedindetailbelow.Thereshouldnormall
beoneplugineachoftheseranges.
-•i:L.I- _ i--.-'.- v'•
MBSA (MemoryBoard §tart Address 1 0 (Startaddress of ZX81 8K ROM)
select;
2 RK_fUt fr£Q locatlon above 8K RCMj
Selectsthepositioninthe64Kaddress^ ,Alr/„, ..._ . . „ '<.
. space oTthe
rZXBl
microprocessor ofthe^ ^ <fcrmal position of start ofW _
mera0^°nTThe
™\>oard+; . -5
:I3?r
(1st Tree'location Shove~15K pack)
Normally setto ,27.30 that memory
f
,„„.
runs from address ^upwards.
? 4gK (lgt free locatlon above 32K
pack)
856K
9Nowhere!(rememoryboarddisabled)
10MBSA( Setifnomemoryonmemoryboard)
11MBSA+2K(Setfor2K(re1 chip)onm boar<
ZES(ZX81(IK)RAMselect), 12MB3A+4K(2chipsonmemoryboard)
13MBSA-r6K(3chips...
14MBSAT8K(4chijs...
SelectsdistanceaboveMBSAofthe15MBSA+10K(5chips...
IKRAMontheZX81boardthusallowing16MBSA+12K(6chips...
ittobeplaceddiatelyabove17MESA+14K(?chips...
thememoryonthememoryboardwithout18Ecohere!(le2X81RAMdisabled)
anygapsandusednormally.
19Unused
20Unused
BSS((Memory)BoardBlockSizedaloct)21Mustbesetifmorethan8Konmemorybn-r
22Setif8Korlessonmemoryboard.
Ifyouwishthememoryboardto23Setifmorethan8Konmemoryboard.
occupyonly8Kofaddressspacemust24Setif8Korlessonmemoryboard.
setpositions22and24.Normalsetting
is21and23(for16Kblocksize).
TRS(TotalRAMSelect)25SetiftotalRAMnotmorethan16K.
_, , -„.,,„,„....26SetiftotalRAMismorethan16K.
EnablesorDisablesAdressline15
toMBSAdecoder,27Unused
Examples;Switchsettings
Sa«4ware_Configuration MSA_^_52£__™5
1.ZX81withoriginal1KRAMstillonZX81boardwithIncremental
containingone2KRAMchip.Noexternalmemory.3 112^>2325
2.ZX81withoriginalIKRAMstillonZX81boardwith.r.cremental
containingfull16KofRAM.Noexternalmemory.3 1821,2325
3.ZX81with16Kadd-onpackandoriginalIKRAMstill5.1ZX81board{£.
withIncrementalcontaining2KofRAM.5 2^21,2326
4.ZX81with. ' IKRAMstillonZX81boardand48lexternal
add-onmemorywithIncrementalcontaining8Kofmemorytogive
themaximumpossibledirectlyaddressedRAM(56K= 6*.C - 8KROM)2 1822,2426

INCREMENTALSERIESRUMIWGALONGSIDEOTHERMEMORIES3
GeneralNotes;
All5AMpackadd-onsof16Koroverknowntous(exceptforourown)havea built-
indisableoftheoriginalIKRAMonthoZX81board.Henoeitisnotpossibletouse
theIKRAMontheZX81boardifsuch-anexternalmemoryisinuse.Aswellasthisitis
necessary toroakethe Incremental RAM selection agre* wdth the •ea-Uiriial fIwyaas^c - ietheZE
plugmustbesetfordibble(seeAppendixB).
Also,itshouldbeunderstoodsthatthedecodingfortheIKand16KRAMSthatexist
inthe ZX81 is onlypartial and ignores bit15oftho address. Ifthe total RAMisnot mor<
than16Kitisasa resultofthisnecessarytomaskbit15oftheaddresstotheTp^rsTnTr
decodingandthisisthepurposeofpositions25and26ontheplug-and-sookeiswitches.
Clearly,ifmorethan16KRAMexistsonthesystemitwillbenecessarytousabit15to•
differentiate "between 16K blocks.Pleaserefer to Appendix B for Jaoatiiogs «£. suujjjzh. setting
abbreviations.
Note- InthefollowingtableofswitchsettingsNCroeand-Noeh-iagefromthecorrect
settingforIncrementalmemoryrunningonitsown,
MBSAZRSBBSTRS
6KKAMpacks
e.g.Sinclair,AudioComputersetc.5 18NG2$
32KRAMpacks,
e.g.AudioComputers.Pins3 and14Of1C3"cn
AudioComputerboardshouldbedirectlyconnectedto
placesecond(16K$halfof32Kattopofmemory(ie
fromaddress* "'\ to64KsothatIncrementalmemorycanbe
placedinbetweenthehalvesgiving48Kofcontinuousmemory.5 ' 18U\26
48KRAMp_acks.
e.g.Jfefflo-t&sli..Theremaining-8Koftho^-1^=^A»aaoCTIw«>»J-js4jo.s
between th«6K -fi©M snriti»« 4GKKAHcanbo occupied bythe
Ino3reni©fitalboardwiththefollowingswitchsettingstogive
the majtimuB possibledirectly addresacsd EAL. of 56K, 2 18 22,^4 £$
6KRAM packs.
Sinclair? Others? The Incremental canbe placed iramGdiately
aboveasfollows.4 182£}24?5
Others
Please call usfor advice onany other packsth-it vnn^*r
rrm*. a-»~-----" - i —•«v/i^cj.-iJii]g-bnupactcsmentionedabove.

INCREMENTALSERIESHINTSandTIPS
Extractingchipsfromtheirsockets.
Takeyourtime.Thedangeristhatyouareexertinga lotofforceandsuddenlyonsgj_r
endofthechipcomesawaybendingtheremainingpinsdrastically.Forthisreasonit:
agoodideatoleverthechipoutwitha screwdriverorpencilthusavoidingsuddenmen
Careshouldhetakebwhenleveringnottodamagethetracksunderthesocket(ifthe$oc
isoftheopenwindowtype),itisusuallypossibletoactuallyleveronthesocket.
Notethat the chip "body is GTctremely rugged - itisthe pinswhich are fragile and v;hicl
willstandonlysomuchbendingbackandforth*
Insertionofchipsintotheirsockets.
Thisismoredifficultthanextraction.Again,donothurry.
Itispossibletoalignthepinstothesocketholes(iegettingthen^straightinline
withtherigtfadistance"betweentherows)bygraspingthechipfirmlybytheendsbotwe
thumbandforefingerandpressinga rowofpinsflatdownonthetablebeingcarefulto
avoidsuddenslips.Oncethepinsarereasonably;veilalignedthechipshouldbeplaced
inthesocket(therightwayround!)withthepinslocatedintheholesinthesocket
plastic(butnotyetintheconnectors). Itcanthenbejiggledintoplacekeepinga
closeeyeforcaughtpinswhicharestartingtobend.
Pinnumbersofchips.
Byconvention,withthechiponthetablebeforeyoustandingonitspinswith
theindentationattheendofthechipbodyawayfromyou,thepinsarenumbered
startingatJ atthefarcornerontheleft,downtheleftsideandbackupthe
rightsidetothefarrighthandcorner.Itisfrequentlydisastroustoinsert
chipsthewrongwayroundintheirsocketiaddapplypower.

IllCHEMEHTALSERIES. — FITTING' 1.1
Youwillrequirea smallconventionalscrewdriver,a smallphillips(crossheadedscrew
screwdriverandtheZX81manual.
RefertoAppendixA fordescriptionofboardlayout.
RemoveallleadsandattachmentsfromyourZX81.
PlaceZX8lontablebeforeyouasfornormaluse.
TurnZX81overasthoughitwerethefrontcoverofa 'book,
PeeloffthefootpadslocatedattheHI,SW,andSEcornersofthebottomofthe2X81J
Completelyloosenthefivesmallrecessedboltswhicharenowvisibleandlightlyreplact
footpadstoavoidlosingthethreecornerscrews.
Liftofthebottomof2X81caseandputitaside.
Removethetwoadditionalboltsnowvisible,rememberingthai*position.
NotethattheZX81boardisnowattachedtothekeyboardhalfofthecasebyjusta thin
ribboncablewhichyoumusttakecarenottodamage.Wedonotrecommendthattheribbon
beremovedfromitssocketontheZX8lboardandthereisnonecessitytodothisifthes
instructionsarefollowed.
takingcarenottostraintheribbonca"ble,turntheZX81board(notthecase)overas
thoughitwerethetopcardona deck(ie.theheatsink(bigrectangleofmetal)goes
undertheboardandawayfromyou).
Turntothechapterinthe2X81manualentitled'Howthecomputerworks'whichcontainsa
pictureofwhatnowliesbeforeyou.NotethepositionsoftheCPUandtheIKHAM,
TakethememoryboardandfindthepositionsoftheROMCSandtheRAMCSdepictedthereon
Withthesedepictionsuppermostandtowardsyou,positionthememoryboardovertheZX81
boardwiththe40protrudingpinslyingdirectlyovertheCPUontheZX81.Thisisthe
positionoffittingwhichyoushouldnowremember.
IftheSinclairIKRAMissocketed(ratherthansolderedtotheZX81board)thenremove
itandputitaside,(seesectionentitled'HintsandTips'foradviceonremovaland
insertionofchips)
RemoveCPUfromZX81andinsertitintomemoryboardbemngsuretomatchindentationatend
ofCPUbodywithpaintspotonmemoryboard.
Removethe14BA.bolts(thereare4)andwashersfromtheirguidesonthememoryboard.
Note- youcouldfitthememoryboarddirectlyinthispositionbutthiswouldnecessitate
theremovaloftheribboncablefromitssocketinordertoturntheboardassemblyback
onitstummyforreassemblyofthecase.- Insteadmakesureyouknowthepoistionof
fittingbeforegoingontonextstep.
SwiveltheZX81heatsinktotheextremerighttobesureofclearingthsraemoryboard
whenfitting.Donotforgettomoveitbacklater!
Turn2X81boardbackonitstummy(iecomponentsdownward).
TurnZX81(includingca.se)round180degreessothatheatsinkisawayfromyou.
LiftZX81boardwithlefthandslippingmemoryboardunderneathitandaroundtheribboncab.
andintopoitionwiththeotherhand(iesothatpinsaredirectlyunderZX81CPUsocket).
CarefullyinsertpinsintoZX81CPUsocketwithevenpressurefromthumbsonCPUbody-
Beextremelycarefultobesurethatall40pinsaregoinginstraightandarenotbending.
Donotinserttoofarintothesocket- thecorrectdepthofinsertionwillbeautomatically
attainedonfittingthefourbolts.
PTO

INCREMENTALSERIES' ' ! TESTING2«]
HavingfittedthememorybeardtoyourZXSl,nowremoveanythingyoumayhavep
intotheexpansionport.Then-
(i)TurnonyourZXSland",raita fewsecondsforthecursortoappear,
iIFthecursorcameupasnormalTHENGOTO(iv).
(111)Thecursorhasn'tcomeupsotryturningonZXSla couplemoretimes.Ifstill
unsuccessfultheproblemisalmostcertainlya badconnectionbetweenthememoryI
andtheZX81board.So-
IPyouhavea multitestcrTfiElT
Testall40pinsoftheGPUconnectthroughtotheZXSlboard.
Testall4 boltguidesconnecttotrackon2X81board.
Checkthatwashersarenotcausingshortson2X81board.
IFallconnectionsseemOKtlunit13likelythatthereisa faultinthe
memoryboard<:oGOTOend- testingfailed,
IFyoudonothavea circuittesterthenremovsthememoryboardandcheckthatno
pinsarebentover.Iftheyareitray"bpossibletostraightenitagainwithout
breakage.Ifonebreaksthenthereisnothingforitbutthesoldeeingiron1
*,iv)FindoutthecontentsofRAMTOP(s^eZX8lmanualifinterested)asfollows-
Typein
PHIHTPEEK16389
theresultwillcomeuponthsscreenandshouldbecheckedagainst
thstable"below.NotethatiftheoriginalIKRAMhasbeenremovedfromtheZXSl
boardthattheRAMTOPvalueshouldbe4 lessthanthefigureinthetable.Ifthisis
thecaseandRAMTOPiscorrectthenyoumayplugintheremovedIKchip(ifitisIK
ofcourse)tothefirstavailablesocketonthememoryboard- atthesametimeyou
ought to move the plugselecting theIK PJLHI to disable(position 18)to avoid the 2X81
decodingfightingthsmemoryboarddecodingandconsumingunnecessarycurrent*
TABLEofcorrectHAAiTO?values.
$fp,of2Kchipsfittedtomemoryboard.CorrespondingvalueofRAMTOP
068
176
284
392
4100
5108
6116
7124
8. 128
IFRAMTOPdoesnotcorrespondtothenumberofmemorychipsthen
Jfotetieactualvalueobtained
Obtainthevalueoflocation16388(typeinPRINTPEEK16388togetthis)andnote
Callus.
end.

-1*2INCREMENTALSERIESPITTING
(Continued)
Positionthefourboltsandwashersbackintotheiroriginalpositionsexceptthatnow
ofcoursetheypassthroughcorrespondingholesintheZX81board.Notethatiftheydo
notpushinfreelytheymaybelightlyscrewedin.
Engagetheboltsinthenutssolderedtotheendsoftheboltguidestotakethememoryi
firmlyuptotheZX81boardestablishinga rigidstructureandfirmelectricalconnectior
betweentheboltguidesandtheZX81boardtrack.Checkthatthewashersarenbtcausing
shortsontheZX81board(thiscanhappeniftheZX8lboardcoatingsarewornaway- the
washersaretheretopreventsuch\vearfromtheboltheads.)
(Notethatitispossibleinthissituationtofitthetopthreememorychipsnexttothe
CPU(ieitisnotnecessarytoseparatethememoryboardfromtheZX81boardinorderto
them))»
IMPORTANT!!!!!!!!!!I !!!!!!!!
IMPORTANTFMM!!!!!!!F!ii'f!
DONOTFORGETTOKOVETHEHEATSINKBACKasfollows- Swiveltheheatsinkhardupagainai
theprotectingpinonthememoryboard- Failuretodothiscancausea disastrousshort
ontheZX81board!
PositiontheboardassemblysnugintotheZX81casetopensuringthatthefourcaselugs
haveclearedtheholesprovidedfortheminthememoryboard.
RefitthetwoboltssecuringtheZX81boardtothekeyboardhalfofcase(inthecorrect
positions).
(Notethatinthissituationthefirstfivememorysocketsareaccessibleaswe&las
all26positionsoftheplug-and-socketswitches).
ReplacethebottomhalfofZX81case- thesecuringofthefiveboltscanbepostponed
tilltestingissuccessfullycompleted).
Test(seesectionontesting).
REMOVING
RemoveallleadsfromZX81.
RemovebottomofZX81case(see'Fitting').
Removethetwoboltssecuringboardassemblytokeyboardhalfofcase.
Removethefour15BA.bolts& washerssecuringthememoryboardtotheZX81board.
Placea mediumsizescrewdriverbetweenmemoryboardandZX81CPUsocketandcarefully
Levertheboardsapartbeing-surenottobendpinsastheycomeoutofCPUsocket.Make
surethatthepointofthescrewdriverpushesontheZX81CPUsocketandnotonboard
trackswhichmightbosodamaged,
FITTINGOFADDITIONALMEMORYCHIPS,
Remove^11leadsandattachmentsfromZX81andremovebottomofcase(See'Fitting')•
Notethatthememorysocketsarenumberedfrom1 to8 (seeAppendixA)andwillnormally
befilledinthatorder.
IFthesockets1 to5narealreadyfilledTHENn n n n , , -,^ ^
v.^twoboltssecuringDoardassemblytokeyboardhalfofcase.
Carefullyplacewholeassemblywithkeyboarduppermostandmovekeyboardtoexpose
memorysockets(donotstraintheribboncable). Supporttheboardwithfingersas
youpluginthememorychiptothefirstavailablesocket(seeHintsandTips).
ELSE IF sockets 1 to5 arenotall filled then sir-rfv -i"~ ^ -v-4- *-- *--"