MIDI In seems to lose bits; where to look?

Testing/Troubleshooting
1

Hi,

first of all, thanks, Thorsten, for this great project! I’ve built a MIDIBox 16 and everything works perfect except for the MIDI In, which seems to lose bits.

Symptom: I connect keyboard->MIDIBox->PC with enabled merger. Note-on events come through correctly about 50% of the time, sometimes they are the wrong pitch, sometimes note-ons come through as note-offs, …

To me it looks as if random bits get toggled from 1 to 0; it´s about one to two bits per note-on/off that get toggled, and always to 0, never to 1.

I have next to no experience with electronics; can anyone infer from this description what might be wrong and can tell me where to look and what to check?

Thanks a lot in advance,

Björn

2

Hi Bjoern,

hrmpf! It seems that I should replace the old CNY17-II optocoupler circuit from the MIDIbox Plus schematics and replace it by the 6N138 circuit, since there are less problems with this part. :-/

If the MIDI interface of your PC or synthesizer is not good enough, the CNY17-II sometimes need small modifications, you can find some debug infos here: http://www.ucapps.de/howtodebug.html

Best Regards, Thorsten.