Sinclair Research ZX Spectrum - Modifications - Issue 2 Board

1.4 Modifications - Issue 2 Board
A number of modifications have also been introduced for the Issue 2
board. These should be checked and, if necessary, introduced
retrospectively.
(a) These components should be changed if colour quality needs
upgrading:
R48 changed from 4k7 to 2k2
R49 changed from 18 k to 8k2
R50 changed from 8k2 to 4k7
R72 changed from 47 k (or 18 k) to 10 k
C65 changed from 100 yF to 22 yF
(b) Early Issue 2 boards were manufactured using a considerable
number of 47 yF and 100 uF disc capacitors. C41 (47 nF) and C43
(100 nF) should be replaced with axial components to prevent
undue risk of short circuits.
(c) To prevent lifting of the keyboard template, a thin strip (6 mm
wide) of double-sided tape was introduced to the top edge of the
template. (Previously, only the other 3 edges had tape). This
modification should be introduced whenever template lifting is
found to be a problem.
(d) See Items 1.3(g) and (h) above.
1.5 Modifications - Issue 3B Board
Although functionally similar to the Issue 3 board, the layout differs.
The DC converter design has been improved, providing greater power
supply reliability. Component changes are as follows (see Fig 1.5 for
details):
C77 (IQOnF) added
C49 changed from 47nF to 560pF
R60 changed from 270fl to 68n
TR4 can be either ZTX650 or TIPP31
1.6 32k Extension Memory - (16k to 48k)
Board Issue 1: The extension memory is supplied as a plug-in module
which is inserted into sockets near the edge connector. The ICs used are
either TI 4532-3 or TI 4532-4, and all ICs in a unit must be of the same
type (i.e. all must be -3 or all must be -4).
Board Issue 2: The extra memory is obtained by plugging in 4 logic ICs
and 8 memory ICs (see Sub-Section 4). The ICs used are either TI 4532-3
or TI 4532-4, and all ICs must again be of the same type. It should be
noted that the RAM select signal is 0V for the -3 1C and +5V for the -4.
A link on the board provides the required select level.
4.5