Today I decided to try replacing all the metal foil caps with ceramics, after about half way through (I'd only done the memory board) I decided to check to see if the thing still worked at low speed and to my surprise it now works at full speed. So two conclusions:
a) It wasn't the metal foil caps causing the problem - the processor, IO and monitor board are covered in them still
b) It must have been some dodgy wirewrapping / soldering near the decoupling caps. I probably melted through a wire sufficiently to allow leakage but not a dead short which was causing problems!
Two feelings after this - elation at getting things working, despair at all the time lost messing about!
Anyway I've now got the LCD interface working reasonably well and written a little scroller - sorry no video, my crappy camera will not take videos of the LCD. Also written a memory soak tester - so far all my 32K RAM tests good!
Next up:
PS/2 keybaord interface
RS-232 interface
CGA/VGA card
SD/MMC Card interface
CP/M
Graphical LCD interface
Not sure which order I'll attack these in but I'd like more info on my intended VGA card (pictured below). Specifically I'd like to know more about the dip-switch settings at the rear. I can see these causing headaches if I get them wrong!
The card is marked MAGIC VGA, CT-8490 and uses the Cirrus Logic GD510A Chipset.
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