MIDI input doesn't work

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MIDI input doesn't work

Postby mrkellystarr » Wed Jul 10, 2019 8:09 pm

Hello, Dmitri!

Today I finally received my Megadrum module that I bought on Ebay several weeks ago. I hooked it up and looks like everything works fine except the MIDI input. My idea is to connect Yamaha DD-65 to MegaDrum via 5-pin DIN MIDI and then MegaDrum to Mac via USB MIDI.

I did some troubleshooting but I wasn't able to get any activity from MIDI input port at all i.e. the red LED doesn't blink, there's no MIDI In message on the MegaDrum's display and there's no activity from the MIDI input in MIDI monitor on my Mac. MIDI over USB and MIDI Out port seem to work OK, though.

The MegaDrum model I bought is 32 input, STM32F205RCT6 based and encased in aluminum. I updated it to the latest firmware. Also, the seller specified that it was built by you personally :)

Here's what I tried:
- different MIDI cables (double-checked them with multimeter so they are definitely OK)
- different MIDI out sources (Yamaha DD-65 e-drums, M-Audio Code 61 keyboard, Korg KP3+ fx unit as well as MIDI data straight from Logic Pro X via MOTU MIDI Express 128 and XT interfaces)
- MIDI Thru both on and off

Any ideas?
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Re: MIDI input doesn't work

Postby dmitri » Wed Jul 10, 2019 10:53 pm

It can be many things:
1. Used MIDI Out instead of MIDI In.
2. Damaged MIDI In port
3. Loose MIDI cable inside the module
4. Mismatch in signal level between Yamaha and MegaDrum. Older MegaDrum modules may require stronger MIDI In signal.
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Re: MIDI input doesn't work

Postby mrkellystarr » Wed Jul 10, 2019 11:54 pm

dmitri wrote:It can be many things:
1. Used MIDI Out instead of MIDI In.
2. Damaged MIDI In port
3. Loose MIDI cable inside the module
4. Mismatch in signal level between Yamaha and MegaDrum. Older MegaDrum modules may require stronger MIDI In signal.


1. No, in all cases source's MIDI Out was connected to MegaDrum's MIDI In.
2&3. After the unsuccessful troubleshooting I unscrewed the top cover and took a peek inside. Soldering job on the MIDI In socket looks fine, so tested it for continuity with my multimeter. The signals from the MIDI In socket definitely reach 2 corresponding MIDI pins on the PCB.
4. I don't think it's a problem because I tested it with several sources (see the first post). And that ARM-based MegaDrum is supposed to be a newer one, right?

Since the socket itself isn't broken and the signal reaches at least those MIDI pins on the PCB, I assume that either something's not right further down in the MIDI Input signal path or it's a firmware bug. What else can I do to pinpoint the problem further?
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Re: MIDI input doesn't work

Postby airflamesred » Thu Jul 11, 2019 12:18 pm

Just as a matter of interest, what are you using MD for and have you tried connecting this the other way around.

koby drums - Triggera krigg/Bix - megadrum - Kontakt........... Samples from all and sundry.
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Re: MIDI input doesn't work

Postby dmitri » Thu Jul 11, 2019 8:54 pm

It's definitely not a firmware bug if you have a latest firmware. I'm afraid there is a hardware problem with the MIDI In port.
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Re: MIDI input doesn't work

Postby mrkellystarr » Fri Jul 12, 2019 4:02 pm

So, I tested the PCB a bit and here's what I've found:

- D2 diode doesn't seem to be blown/shorted/open
- All resistors in the signal path (R34, R29, R30) seem to be OK (their values show up properly when tested with multimeter)
- The signal definitely reaches pin 43 of the STM32 chip
- When I tested the voltage of the VCC point near 6N138N IC it only showed 3.3 volts (see the attached file). Is this OK?

Any thoughts on that? Low voltage at the VCC point? Bad 6N138N?
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Re: MIDI input doesn't work

Postby dmitri » Fri Jul 12, 2019 11:26 pm

It can be a bad 6N138 but it can also be a bad pin on STM32.
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