MIDI Input is shot

Hello everyone,

I was able to successfully build my very first synth the other day (the Shruthi-1) and was so happy that I tested it out. I used my MIDI controller directly and was able to get sound (after 3 tests). Then I tried to use my Audio Interface (Motu Ultralite Mk3) and used the MIDI Out to the Shruthi’s MIDI in. The weird part was that the LED screen was lit a little so it must’ve been receiving some power from the MIDI In. I plugged in the Power Supply (12v 500mVA) and everything booted up, I walked over to the computer and heard a little *pop and afterwards heard only pops and clicks from any MIDI signal.

Bummed, I tested the MIDI controller again (CME UF80) and same results. I then looked at the Main Control board and saw some damage near the MIDI In. It looks a little shot but everything else works great on the board, and I also see a note every time MIDI in is sent to the Shruthi (the note on the right). I still only hear pops and clicks though.

If you need anymore information I’ll be happy to assist as I am worried I need a new Main Control board… which sucks because this is the only part that isn’t working correctly. I was hoping that I may be able to swap my MIDI since I won’t be using MIDI Out for anything. If there are steps to do this please let me know. I was also curious if anyone gets power from their MIDI device? Should this happen or do I need to do something to prevent this?

I don’t think there should be power from you midi device. Maybe there is some problem with you motu… Could you post a picture?

By no means you can power the Shruthi from its MIDI IN Port, its isolated by the 6N137 Optocoupler, there is no galvanic (which means a direct conducting) link between the Shruthis circiutry and the MIDI Interface. All whats happening inside the Optocoupler is your MIDI Interface driving a LED, the light triggers a light sensitive Transitor and this Transistor generates the Signal thats passed to the ATmega. Check the Schematics (lower left corner)-

So what really happened was you plugged your MIDI Out from the MOTU to Shruthis MIDI Out which is directly connected to the ATmega (which you may have fried this way) and via a 220R to Vcc. That is the way the Current took from your MOTU, flowing into your positive Rail, not enough to Power the whole thing albeit enough to light the LCDs backlight LED.

You can’t swap the both ports as they are in different physical configurations and you would also need to change the behavior of the ATmega by altering the Firmware.

BTW, 12V is a bit much, your regulators (7805, 7905, LT1054) might get a bit hot

It’s not powering the entire Shruthi, but when I plugged in my 5 pin din into the Shruthi, the LED display backlight (only) did fire up. The LCD lights did not fire up and the Shruthi did not start. This only happened when I plug in my MOTU. I will try other sources when I get home from work (though after the pop, it does not light up anymore like it did when the accident occured). I can confirm it is the MIDI input, I double checked the User Manual (also get the eight note blink every time MIDI signal goes to Shruthi). The trace from the input plug to the 220 resister (and the D1) is where I see some singe. The ATmega chip appeared to look great when I lasted checked (fcd72, I will give it one more look though to double check).

@ shftr (I will keep my MOTU in mind as it is definitely a possibility. From the amount I use it and with all the different configs of my studio, I don’t think it is though).

I kind of figured that 12V was too hot and my regulators are getting hot. I’ll definitely switch power supplies for long term use (I was only using this one for testing, probably a bad idea).

Thanks for the advice, I really appreciate it. I’m just hoping there is a work around for this but if there isn’t I understand my noob mistake. Definitely will never underestimate how hot I can get a newly built device. This will also work better I’m sure if I had a picture for you, I will post one as soon as I get home tonight.

Again: if the LCD backlight lit up you accidentally have plugged in the MIDI connector into the wrong jack and might have damaged the ATmega. What you described is exactly what happens if you swap MIDI In and Out, trust me, i know what I’m talking about…

There is no physical way how any current can flow from the device on the MIDI Input to the Shruthi, so you must have it plugged in the wrong jack - or your Shruthi is different from all of mine.

And you don’t necessarily see if a chip is fried, in fact all of my dead chips look just brand new. There is no workaround for a damaged Chip, you can only replace it with a working one.

So lets check if you damaged your ATmega, MIDI in is working as far as i understand, check if MIDI out is working also (Set MIDI to full and tweak the knobs. There should be heavy MIDI Traffic be visible in your whatever-software-you-use.

fcd72, I work in technical support for music software and troubleshoot at a full time position. From my experience with my job, I’m telling you exactly like it is to my best ability so that I can seek the best solution possible.

I can 100% confirm that I plugged into MIDI Input and saw display backlight turn on. You are the expert and I believe you that it’s not possible but this is what I saw. If I didn’t, I wouldn’t have brought it up. (I cannot replicate the issue so you got me on this, also swapped power supplies to a 9V). Thank you for the advice.

Got home and tested out the Shruthi-1. MIDI works and I get playback (just read 2 posts today with same outcome, weird). I am attaching the picture of the singed area (wish I had a better camera sorry).

fcd72, thank you again for you help. I have an extra ATmega chip lying around so if I continue to get this issue would you suggest swapping them for troubleshooting purposes?

If you have a extra ATMega lying around, try swapping them, if nothing else to confirm or not whether fcds suspicion is correct :slight_smile:
I’m personally guessing a short waiting to happen somewhere(That then happened), but fcds suspicion sounds like a winner to me :confused: (Not helped by the amount of times he has had the possibility of doing something like that - He’s probably an expert on weird ways to f… up your shruthi )

Yups V’cent, i probably trashed a Shruthi each possible way at least once.

Maybe plugging you MOTU to the midi in somehow made a ground connection (looking at the scematics this should not be) and made some power still left in the capacitors in the shruthi light up the LEDS. Other possibility is that there is somehow mains power (240V) on you midi from the MOTU. This should damage the shruthi and by sparking probably light up some things on the way. Again could you post a picture of what happened to you board?

@shiftr I can pretty much guarantee that there is no mains power coming from the motu, since A) It doesn’t run on mains power to my knowledge, and B)It’s pretty damn sure to be optically isolated from the rest of the circuit… That said, if someone tinkered with it - who knows?

You CAN power (at least partially) via the midi OUT connector… no optocoupler there…

Thats what i pointed to ByteFrenzy…

I see now you already posted a picture. It’s very vague i can’t see what happened there. Can you check the OSC signal on your control board? See the bottom of this page how to do it. If you see a not in your display the midi and the MCU works fine so there must be an other problem. Maybe a bad connection between the 2 boards.