I cant seem to easily locate an answer to this, but when viewing Trash80's original schematic are the 5 pin DIN connectors being viewed from the face or the rear?
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From the back if you refer to the simple drawn schematic on code.google. here's a picture to help you even more.
This if from mine, I DID IT WRONG! 
, (photo of midi output) again, take note: my resistor is on the wrong side! should go to the leg the arrow points at.
Don't pay attention to the crappy soldering haha
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Sweeeeeeden
That schematic is sloppy in ways. The MIDI in and MIDI out jacks are actually mirrored compared to each other. And the 220 ohm resistor in the input side has the wrong markings. (Grey band instead of brown. Brown is correct.)
In:
Pin 4 to 220 ohm resistor to pin 2 of the optcoupler.
Pin 5 to to pin 3 of the optocoupler.
On the in connection, also note the polarity of the 1n914 diode. This is a protection diode, and if it's reversed, no signal will come through.
Out:
+5V to 220 ohm resistor to pin 4.
TX to pin 5.
How do you know which pin is 4 and which is 5 I hear you ask? Look at the socket! Most likely, there are little numbers molded into the plastic. If not, cross reference with the jack of some other MIDI gear.