I've got problems with A500 RAM expansion. It was bought recently (A500 and expansion) and in bad condition. It worked for a while (512kb chip+512kb other), but after 30 min or so crashes started. The A500 wouldn't boot after reset. So, I tried it without RAM expansion, and it worked. When returning expansion into A500, the fast memory is 0kb.
Strangely battery backed clock works fine, though everything is quite old and dirty.
I would have examined the expansion closely, but its completely soldered into metal box (sort of triangle shape)
I'd prefer not unsoldering it (if its not necessary), not to spoil the "look". :-)