The requirement was that all upgrading would not detract from the basic machine and would be entirely reversible. The machine I bought had already been upgraded by the previous owner;
- a 300/600 baud switchable cassette save mod,
the 48 chars by 32 lines VDU upgrade
an up-rated PSU
Another problem I had was the machine ran very hot. The PSU for the basic UK101 was really at its limit even with just a basic board. My intent was to reduce the current needs of the computer by using modern components.
My first upgrade then was to replace the 8K on-board user RAM with a 32K CMOS static RAM. One of these chips would use only a fraction of the power of the original chips and give a massive increase in memory. The upgrade I made is a plug-in carrier board and needs no other connections.
The second photo is the screen just after booting and shows proof of concept. The pdf gives a circuit and further photos.
Now I have 32K, saving to tape is excruciatingly slow! My next upgrade will be to add a 6522 or similar to interface to a Raspberry Pi running RISCOS pico. The Pi will act as a backing storage device controlled by the UK101 through the 6522-GPIO link.
Watch this space - eventually!