I have an even more frustrating Midi-to-Pic problem.
I have a setup, using a standard circuit (using a 138), that I thought was
finished.  We used it for several days and it worked flawlessly, reading
all MIDI input correctly.  Then we used it with different MIDI devices, and
it barfs.
It is hard to describe, but there is some threshhold of speed, which varies
by the device, above which bytes get dropped.  The original MIDI device we
used for testing does not cause this behavior at all, and works perfectly
no matter how hard we drive the circuit.

What could be the trouble?  At this point, after extensive testing, we are
certain it is not a software problem.  Some devices work, others don't.
Our best guess is that some devices produce a weaker signal, or a crappy
waveform, which causes our opto to produce a mushy signal which the PIC
fails to read.  Is this possible?

Unfortunately, no, I don't have ready access to a scope.
Is there some way we could amplify the output of the opto?  Or of the
signal coming from the current loop?  Or should we get a higher performance
opto?  Perhaps one with logic level out?

Any suggestions are welcome.
Thanks,
Dan Walkowski & Bill Walker