6N138 instead of 6N137

I couldn`t find 6N137 in my country, so I used 6N138 as it is suggested as a good replacement for the original optocoupler.
The problem is that 6N138 didn`t worked as expected. On display, shruthi is showing strange symbol when sending notes, and symbol # when sending CC controls but no sound produced. If I didn`t get any sign at display, I would suspect at optocoupler but it seamed that ATMEGA is receiving MIDI as it is showing some symbols when sending MIDI.
I have used 6N138 on various MIDI projects and noticed 10K pullup resistor is never used. When I decreased the value to 1K, MIDI worked and shruthi starts singing. 1.5K value was also fine, but 4K7, that I tested before 1K, wasn`t.
It would be good to mention in documentations, if 6N138 is used indtead of 6N137, pullup resistor value should be decreased to 1 or 1.5K.

I regret I can’t document any “part substitution” which is not an equivalent part substitution! If you decide to use a totally different part in your build, it is your responsibility to understand what the substitution implies, and adjust the circuit accordingly.

The 6N137 is a different affair from the 6N138 and needs to be calmed down with a high pull-up to avoid transient leaking on the board. The 6N138 is slow, barely fast enough for MIDI, and needs a low pull-up (220 or 470, 1k if you’re paranoid about noise).

Mate, is is not about responsibility. :slight_smile: I just said it would be good to mention that other resistor should be used with 6N138.
6N138 is not “totally different part”, it is part that is suggested on the troubleshooting page.
I`m planing to use 6N137 when I get it, even I didn`t noticed some speed problems.

I have removed the bit about the 6N138 on the troubleshooting page, since it applied to the v0.5 boards.