these are the main operating system chips for the synth. 2 of the chips are for the main rom and the other two are for the tone generator system.
dont know if you have upgraded yours yet but i have done mine twice.
the chips are free from yamaha but they specify that you return your old chips.
for more info on the ex5 have you tried ex5 tech ? It is the best site for info and patches/samples.really great! http://www.wbmedia.com/ex5/
ps, make sure you check the discussion forum.
[This message has been edited by mick n (edited 01-19-2001).]