Module replace the eight 4532 or equivalent chips form the upper 32Kb of RAM in a 48K ZX-Spectrum computer issue 2 or later. Or upgrade a 16K ZX-Spectrum to a 48K.
As you know, memory chips for old computers have not been produced for a long time, the quality of the chips themselves leaves much to be desired, they often fail due to time or power supply problems. The module uses a modern low power CMOS technology SRAM memory chip.
The upper RAM needs IC23, IC24, IC25 and IC26 chips.
If 16K ZX-Spectrum, support logic for the upper RAM must be installed. On earlier boards these chips mark IC23, IC24, IC25 and IC26. On later boards issue 6 this logic is contained in a single 40-pin chip IC27.
Intallation
To install the module, you need to: disassemble the computer, carefully disconnect the keyboard cables, unscrew the central screw holding the main board and remove it from the case. Desolder all eight 4532 or equivalent chips (IC15-IC22), carefully check all connections and tracks, because there is a risk of damage if you unsolder carelessly. Install eight standard 16-pin DIL panels, please note that collet (round pins) panels are not suitable for this replacement board.
WARNING: The module mounting pins may be sharp, take care when handling it. Observe static precautions when installing the module and store it in an anti-static bag until installation. CMOS type components that are easily damaged by static electricity.
The pins should be perfectly perpendicular to the lower surface of the module circuit board.
The module should be aligned squarely over the row of DIL sockets, using the pin 1 indicator to orientate it of IC socket IC22 (the top left pin) and that the board is mounted squarely so that all the other pins are aligned correctly, when viewing the ZX-Spectrum PCB from above and the front.
Then slowly and evenly press the module into the sockets. Press down on the module circuit board rather than its components.
On motherboards issue 4S disc type ceramic capacitors used which may be an obstruction. If they cannot be folded down out, they can either be removed or replaced with smaller 22nf ceramic capacitors.
When installing the module, take care to make sure that all its pins are properly inserted into the correct socket contacts.
Alternatively the upper RAM module can be soldered directly to the ZX-Spectrum PCB without the use sockets. In this case, it is necessary to make a gap of two millimeters from the ZX-Spectrum board.
Place the ZX-Spectrum PCB back into the case. Power up, you can test the computer without the keyboard membrane attached. Computer should boots to the copyright screen, disconnect the power and proceed with assembly. Push the membrane tails back into their sockets, place the top section of the case.
Jumper links
The jumper links settings should be installed for this PCB module, valid configuration should still be set:
Issue 2 board – on the top right of IC1 (ULA chip) there are 3 pads, the top is marked +5v, the bottom is marked 0v. The upper pad must be connected to the central one.
Issue 3-6 boards – on the right of the MIC socket, under the heatsink, there are two groups of pads marked TI and OKI, must be connected TI linked and 3 linked.
Issue 2 boards have a heatsink in the bottom right and all other issue PCBs have the heatsink at the top, of the edge connector.