i tested the MIDI IN of my MIDIBox like decribed in “The Hardware Debug HowTo” without success. 
I connected a test-LED between Pin 6 of the optocoupler (Pin 26 of the PIC) and Vss. I thought the LED will flicker, but she dont. There is all the time 4.96V and no change while sending MIDI to the Box.
Maybe the Optocoupler is damaged?
Could anyone make the test with a LED or measure the Voltage?
THX
hi,
try putting a LED on the input side of the photocoupler.
This will verify absolutley that you have MIDI-IN right up to the opto and tests for all connections and polarity up to this point including the generator of the MIDI stream.
1.Temporarily disconnect pin3 of the opto, also one side of D1 .
2.Connect a red led in place of D1 pads.
If the LED does not flash when MIDI is sent, reverse the polarity of the LED.
If the LED flashes check the polarity of the wiring to the MIDI connector.
5.If things are wired correctly when the LED flashes its cathode (-ve) should be attached to annode of D1 (pin 3) .
THX Duggle!
the test was positive and still no MIDI-IN ???
The MIDI signal is present on the input side of the opto, LED flashes. Then the D1 soldered instead of LED, swaping annode und cathode.
I allready changed the opto…no MIDI-IN
Is it the PIC…? ??? I will test a second one.
PS: for test pruposes The PIC is programed with the rxtx-test firmware.
hello,good .
1.Now remove PIC and wire a LED in series with R6 (annode of LED towards +5V).
When MIDI data is recieved, Pin 6 of IC2 will switch to ground, pulling current through the LED.
Now if the LED flashes, you have all MIDI circuitry working and can concentrate on the programming of the PIC.
[if your not having success with this test]
You said you measured 5V on pin6, make sure this node is not somehow shorted to +5V. Also check that you do have ground to pin5 and +5V to pin8.
Problem solved ;D
I made your test, but the LED dont flash.
The PIN of IC2 was allway “high”.
Then i checked pin6, pin5, pin8… there was allright.
And before i connected 220V to MIDI IN 
i removed the 220ohm resistor (R11) before opto and the MidiBox received MIDI 8)
Is it ok to let this resistor out, or can i damage the opto?
I disconnected the power immediately.
PS: I will drink some beers to your health tonight!
Big thanks!
well done.
I Think the MIDI spec guarrantees a series resistance at the MIDIOUT end, but I’d test it with 100R and use that.
[its good to have some local current limiting!]
best regards