The circuit diagrams for several different variations of this model are here:-
http://www.zimmers.net/anonftp/pub/c...001/index.html
If you can find a 32...... board number on the mainboard that would be helpful, and also report which sort of RAMs and which sort of ROMs are fitted in the PCB, that will help us to narrow it down to the diagram which best matches your computer.
I agree with Mark that the initial problem seems as if it may be in the display area rather than the overall CPU area - it looks as though the CPU is running to the extent that it fills the screen memory with spaces and then the startup message, but both the spaces and the startup message are being displayed incorrectly.
If you had a scope then you could (in conjunction with a test EPROM) try to narrow down the area of the fault without disturbing the actual hardware too much.
Without a scope you have to resort to cruder methods which may ultimately include replacing the display RAM and its support ICs, starting with the ones which are the cheapest to buy and easiest to replace. (So usually, you would replace the display RAM last).
You may also have a secondary problem in the form of a mostly none working keyboard but that will be easier to diagnose and fix with a fully working display, so fixing the display is the priority.
If you can first let us know the PCB number and the types of ROM and RAM IC fitted, we can then begin to make suggestions about how to proceed.