MIDI not working [solved]

I just finished assembling my first shruthi.
Everything seems to be working except the MIDI-In (and perhaps Out).

I have checked that all the IC’s are in the correct socket and correct alignment.
I have checked and rechecked all the solder points around the MIDI-connectors.
I tested my MIDI-keyboard with my other synth, an electribe, and it works as usual.

Unfortunately I have already soldered the LCD in place so I can’t easily check the
soldering behind that.
(I know, stupid… but I didn’t realize I could test it without soldering it)

I havn’t checked if the MIDI-Out is working because I don’t know how…

Is there any pin(s) I can probe to se if the Shruthi is receiving MIDI-data?
I only have a multimeter for testing, no fancy scopes or anything :slight_smile:

as far as i know a note symbol should be displayed in the LCD on incoming midi notes.

Im in the same boat with midi in. I will be following this with thread and I will share any progress I make.

rosch: Yes, I forgot to mention that… I get no note symbol in the display either.

The pin 6 of the optocoupler should be most of the time at +5V and temporarily pulled down down when there is incoming MIDI data. On a scope, you should be able to observe signals like this:

With a meter, the change is so short that it will only make the last digit flicker. Do you have other MIDI sources that you could try?

I just tried outputting a sequence from my electribe.
Pin 6 on the OK1 flashes from 4.96V to 4.95V in sync with the tempo of the sequence.
I would assume this is a short drop to 0V.

Ok, I did some more measuring on the OK1.
Pin 1 is the top left, with the indented dot, yes?

1-| o |-2
3-| |-4
5-| |-6
7-| |-8
No incoming MIDI:
1- 0,44-0,45V
2- 5,00-5,01V
3- 0,45V
4- 0,44-0,45V
5- 0,44V
6- 4,95-4,96V
7- 0,45V
8- 0V

Sequence of MIDI-notes:
1- No change
2- No change
3- 0,65-0,8V
4- No change
5- 0,46V
6- No change
7- No change
8- No change

I know those values don’t give much information, but I don’t have access to a scope…

Where do I go from here?
Is there anything else I could try before de-soldering the display to check for bad
connections to the MCU?

I am so very sorry for taking up your time with this :frowning:
Feeling ashamed right now…

I had somehow managed to switch the IC4 and OK1.
Realised this when I tried to access the presets for the first time.

The text is so tiny tiny.

MIDI works, presets work… Think everything else works too!

Cool! Lazerbeat, have you checked that you haven’t swapped the chips too?

Hey there. I did double and triple check. I havent swapped the chips. Also I can see all 80 presets which I think indicates the chips are in the right place?

Im wondering if my multimeters batter might be dying. I will get a new one this afternoon and re test.

Ok, yeah looks like my multi meter had faulty batteries… With new batteries on pin 6 I get plus 4.93 with midi off and with midi on variations between plus 4.93 and plus 4.86. These voltages seem a little low to me. Im assuming I have a resistor in the wrong place. Im going to check the board and parts again.