Analogue-sequencer

Folks,

I've been having a look at the occasional problems of non-
functioning 6N139 opto-isolators, and come to the conclusion that 
the resistor values specified up until now are not suitable in 100% 
of cases.
I know Andy had a problem with one, I suspect Keith's upgrade 
problems are caused by it, and I've got a new ready-built unit here 
that was exhibiting the same thing.
The values I use are based on a reference in a book I've had for 
years, although I've increased the load resistor myself when I've 
had trouble before.
I had a look at all the midi input circuits based on 6N139s I could 
find on the web today, and there seems to be no consensus at all as 
to what they should be. The datasheets for the part are pretty vague.

So, if you find you get BAD DATA warnings while flashing, first try 
removing R3. If that doesn't work, try replacing R3 with 10k.