Editing Psion Series 3a (section)

== Inside ==

[[File:Psion Series 3a open.jpg|thumb|420px|A German-keyboard 3a. The icon strip above the keyboard is the '''button bar''' — a separate PCB with its own ribbon cable to the mainboard, and one of the two commonest fault points on the machine.]]

The mainboard carries the '''large square Psion custom ASIC''' on the left, the '''ROM''' at the far right, and the '''SRAM devices inboard of the ROM'''. A 256 KB machine has '''two SRAMs fitted and spare solder pads for two more''' — which is what makes the 512 KB upgrade possible.<ref name="pb-ram">David Kimberlin-Wyer, [http://www.primrosebank.net/computers/pda/psion3a/projects/ram_upg/psion3a_mem_upg.htm "Psion Series 3a Memory Upgrade"], primrosebank.net. Source for the 18-step disassembly procedure, the board layout, the spare SRAM pads, the two keyboard membrane types and the reassembly caution about the bowed button bar.</ref>

Fitting two more SRAMs takes a 256 KB machine to 512 KB. The original devices were Sony parts; at least one attempt with Hitachi 628128 devices produced a "'''Memory corruption'''" message, which suggests the substitute was not compatible.<ref name="pb-ram" />