Sinclair ZX81, Assembly Instructions Manual, Page: 20 / 43

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INCREMENTAL SERIES PITTING
(Continued)
Position the four bolts and washers back into their original positions except that now
of course they pass through corresponding holes in the ZX81 board. Note that if they do
not push in freely they may be lightly screwed in.
Engage the bolts in the nuts soldered to the ends of the bolt guides to take the memory i
firmly up to the ZX81 board establishing a rigid structure and firm electrical connectior
between the bolt guides and the ZX81 board track. Check that the washers are nbt causing
shorts on the ZX81 board (this can happen if the ZX8l board coatings are worn away - the
washers are there to prevent such \vear from the bolt heads.)
(Note that it is possible in this situation to fit the top three memory chips next to the
CPU (ie it is not necessary to separate the memory board from the ZX81 board in order to
them))»
IMPORTANT!!!!!!!!!!I !!!!!!!!
IMPORTANTF MM!!! ! ! ! !F ! ii ' f!
DO NOT FORGET TO KOVE THE HEAT SINK BACK as follows - Swivel the heat sink hard up againai
the protecting pin on the memory board - Failure to do this can cause a disastrous short
on the ZX81 board!
Position the board assembly snug into the ZX81 case top ensuring that the fourcase lugs
have cleared the holes provided for them in the memory board.
Refit the two bolts securing the ZX81 board to the keyboard half of case (in the correct
positions).
(Note that in this situation the first five memory sockets are accessible as we&l as
all 26 positions of the plug-and-socket switches) .
Replace the bottom half of ZX81 case - the securing of the five bolts can be postponed
till testing is successfully completed).
Test (see section on testing) .
REMOVING
Remove all leads from ZX81.
Remove bottom of ZX81 case (see 'Fitting').
Remove the two bolts securing board assembly to keyboard half of case.
Remove the four 15BA. bolts & washers securing the memory board to the ZX81 board.
Place a medium size screwdriver between memory board and ZX81 CPU socket and carefully
Lever the boards apart being- sure not to bend pins as they come out of CPU socket. Make
sure that the point of the screwdriver pushes on the ZX81 CPU socket and not on board
tracks which might bo so damaged,
FITTING OF ADDITIONAL MEMORY CHIPS,
Remove ^11 leads and attachments from ZX81 and remove bottom of case (See 'Fitting')•
Note that the memory sockets are numbered from 1 to 8 (see Appendix A) and will normally
be filled in that order.
IF the sockets 1 to 5
n
are already filled THEN
n n n n
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.^ two bolts securing Doard assembly to keyboard half of case.
Carefully place whole assembly with keyboard uppermost and move keyboard to expose
memory sockets (do not strain the ribbon cable) . Support the board with fingers as
you plug in the memory chip to the first available socket (see Hints and Tips) .
ELSE IF sockets 1 to 5 are not all filled then sir-rfv -i"~ ^ -
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