Sinclair Research ZX Spectrum - Page 34

(a) for a 48k unit - 65535
(b) for a 16k unit - 32767
The value printed in each instance is the last valid memory location,
and in a serviceable unit would be as set out above. Therefore, if a
different value, n, is printed the faulty location will be n + 1. If
the value returned is less than 32767 the fault lies in the original
16k of RAM. The following example illustrates the method of relating
a faulty location to a faulty 1C.
Example. If a 48k Spectrum is giving a memory of 25.25k key in the
following instruction:
PRINT PEEK 23732 + PEEK 23733 * 256
Assume the answer displayed is 43200, therefore the faulty location is
43201 (stops at last valid location). Key-in:
POKE 43201,85 : PRINT PEEK 43201 (= answer A)
If answer A is 85, key-in:
POKE 43201,170 : PRINT PEEK 43201 (= answer B)
If answer B is anything other than 170 look up in the following table
which 1C to change (e.g. if answer B is 234 change IC21). Similarly,
if answer A is other than 85 refer to the table to find the faulty 1C.
Data 85 Data 170 Size of Error Faulty RAM location if:
IC6-IC13 IC15-IC22 Error Bit < 32767 > 32767
84 171 1 0 IC6 IC15
87 168 2 1 IC7 IC16
81 174 4 2 IC8 IC17
93 162 8 3 IC9 IC18
69 186 16 4 IC10 IC19
117 138 32 5 IC11 IC20
21 234 64 6 IC12 IC21
213 42 128 7 IC13 IC22
If there is more than one faulty RAM location the first fault
identified will have to be repaired before it is possible to proceed.
4.9