🚀 go-pugleaf

A program I wrote creates a string of 256 notes and sends them out the MIDI  
port one at a time.  The problem is, it never gets through the whole string.
I don't think it's a software error because: 1) It never stops at the same
place, sometimes it gets through 150 notes, sometimes only 5, and 2) there is
no random function in the program that could explain this.
 
What happens when the notes stop is that the monitor blinks and the disk
drive starts up (usually).  Sometimes I get 4 bombs, if the monitor doesn't
go nuts.
 
Any experienced music hackers out there?  What do you suspect?  The cables?
The optoisolator?  My DX-7?  A bad chip?  Or if it's software why doesn't it
bomb at the same place every time?
 
(Possible hint: I am using timer C when sending the notes.)
 
 
-- Guy Ridley