Sinclair ZX Spectrum Service Manual
Spectrum For Everyone https://spectrumforeveryone.com/
23
4.3 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.
• These components should be changed if colour quality needs upgrading:
R48 changed from 4k7 to 2k2
R49 changed from 18k to 8k2
R50 changed from 8k2 to 4k7
R72 changed from 47k (or 18k) to 10k
C65 changed from 100uF to 22uF
• Early Issue 2 boards were manufactured using a considerable number of 47uF and 100uF disc
capacitors. C41 (47nF) and C43 (100nF) should be replaced with axial components to prevent
undue risk of short circuits.
• To prevent lifting of keyboard template, a thin strip (6mm 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.
• See Modifications - Issue 1 Board, the last two.
4.4 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:
• C77 (100nF) added
• C49 changed from 47nF to 560pF
• R60 changed from 270R to 68R
• TR4 can be either ZTX650 or TIPP31
4.5 32K EXTENSION MEMORY - (16K TO 48K)
4.5.1 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).
4.5.2 Board Issue 2:
The extra memory is obtained by plugging in 4 logic ICs and 8 memory ICs (see here). 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 IC and +5V for the -4. A link on the board provides the required select level.
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