Sinclair ZX81, Руководство по сборке, Страница: 19 / 43

INCREMENTAL SERIES ' ' ! TESTING 2«]
Having fitted the memory beard to your ZXSl, now remove anything you may have p
in to the expansion port. Then -
(i) Turn on your ZXSl and ",
r
ait a few seconds for the cursor to appear,
i IF the cursor came up as normal THEN GOTO (iv).
(111) The cursor hasn't come up so try turning on ZXSl a couple more times. If still
unsuccessful the problem is almost certainly a bad connection between the memory I
and the ZX81 board. So -
IP you have a multitestcr TfiElT
Test all 40 pins of the GPU connect through to the ZXSl board.
Test all 4 bolt guides connect to track on 2X81 board.
Check that washers are not causing shorts on 2X81 board.
IF all connections seem OK tlun it 13 likely that there is a fault in the
memory board <:o GOTO end - testing failed,
IF you do not have a circuit tester then removs the memory board and check that no
pins are bent over. If they are it ray "b possible to straighten it again without
breakage. If one breaks then there is nothing for it but the soldeeing iron
1
*,iv) Find out the contents of RAMTOP (s^e ZX8l manual if interested) as follows -
Type in
PHIHT PEEK 16389
the result will come up on ths screen and should be checked against
ths table "below. Note that if the original IK RAM has been removed from the ZXSl
board that the RAMTOP value should be 4 less than the figure in the table. If this is
the case and RAMTOP is correct then you may plug in the removed IK chip (if it is IK
of course) to the first available socket on the memory board - at the same time you
ought to move the plug selecting the IK PJLHI to disable (position 18) to avoid the 2X81
decoding fighting ths memory board decoding and consuming unnecessary current*
TABLE of correct HAAiTO? values.
$fp, of 2K chips fitted to memory board. Corresponding value of RAMTOP
0 68
1 76
2 84
3 92
4 100
5 108
6 116
7 124
8 . 128
IF RAMTOP does not correspond to the number of memory chips then
Jfote tie actual value obtained
Obtain the value of location 16388 (type in PRINT PEEK 16388 to get this) and note
Call us.
end.