The Z88 Upgrade Page 4

As already mentioned I started out by merely replacing the RAM chip with a 1M static RAM. These come from RS in a plastic chip carrier. The pressure of the pins makes these bow outwards. Press this in to make the sides parallel, which will better align the pins with the socket. Then locate one side of the pins, in the correct orientation, into the socket. If you then push back against this side of the socket, you will be able to slip in the other side: once located, fully push the chip in. Note, that I have not bent out pin 30, as recommended in some accounts. This would be pin 28 of the original chip and hence the +5 volt supply. I noticed in the chip documentation, available as a previously mentioned PDF, that pin 30 of the Samsung RAM is in fact chip enable, CE, which is active high. The chip won't work at all if there is not five volts on this pin. The only time that this line should go low is when the chip goes into suspend mode. I am looking into generating an appropriate signal for this, as the power consumption of the chip is minimal when in this mode, which should be when the computer is actually switched off.

Before any re-assembly, the case needs modification. The under side of the keyboard has a series of diagonal and box shaped ribs to stiffen it. These have already been removed during manufacture to allow for the extra height of the EPROM in it's socket. We must make a similar modification, to take account of the RAM chip in it's socket. For this I used a small pair of end cutter pliers. It was easy to snip through the quite soft plastic.

We are now in the position to re-assemble. I have not mentioned replacing the ROM, as I would like to see that it works, before screwing all back together again. An application of Occam's razor, if it doesnt work, we have reduced the number of variables to one, by replacing just the RAM! We can reconnect everything, without screwing the case together. Take great care when refitting the tongues of the display and keyboard ribbons. They must not be cracked, and this is easy to do if you bend the ribbon through too sharp an angle, Some pressure is needed to refit, particularly the keyboard ribbons. Once all is reconnected, plug in the powersupply, batteries will not fit without complete assembly, and the screen should flash on, probably a blank, blue, shimmering display, which should clear once you have pushed the re-set button twice. If this is all you intend to do, re-assemble in the reverse order to disassembly on page two.

I intend to update this with the instructions for fitting the 512K and an upated ROM at a later date (the EPROMs and 512k RAM I have ordered havn't arrived yet).