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MIDI IN not working
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MIDI IN not working

by jorrit on Wed Nov 15, 2017 9:44 am

Recently I made my x0xb0x. The kit is bought at x0xsh0p.de. Everything seems to work excellent, except for one thing: MIDI IN.

Both MIDI play and sync are not working. I focus on MIDI play (both in practice and in this topic). The x0xb0x does not respond in any way, also no LED's are flashing, so to speak.

MIDI THRU is working as expected. Imagine I have set channel 1 on the x0xb0x and channel 2 on a Volca Keys. When I use Ableton to play notes to channel 1, the x0xb0x does not respond. When I let Ableton play the same notes to channel 2 and I connect a Volca Keys on MIDI THRU of the x0xb0x, the notes are played on the Volca Keys, just as expected.

Also MIDI OUT is working as expected. Notes played on the x0xb0x are received just fine in Ableton.

MIDI settings in Ableton are double-checked and seem to work, as confirmed by the Volca Keys. I tested with a USB-to-MIDI cable from Ableton, but also from a MIDI-to-MIDI cable from a MIDI controller.

My problem looks the most like this post (except for the cause): viewtopic.php?f=12&t=21479
The helpful guest in this thread is suggesting to measure the resistance from the point where Q50 and R15 meet back to pin10 on the microcontroller, but I don't understand which microcontroller he is talking about.

I suspect the failure is somewhere in the connection of the IO board and the mainboard. How can I test and measure some things? I have a multimeter and an oscilloscope.

Thanks in advance for your help.
Last edited by jorrit on Thu Nov 16, 2017 3:55 am, edited 1 time in total.

jorrit
 
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Re: MIDI IN not working

by antto on Wed Nov 15, 2017 2:39 pm

jorrit wrote:I read somewhere that MIDI THRU could be used as MIDI IN, but in my case this does not work either.

you've interpreted it a bit wrong
the "THRU" on the x0xb0x is generally supposed to be a buffered copy of the signal on the MIDI "IN"
this is useful if you have (for example) a drum machine acting as a MIDISYNC master, and two (or more) x0xb0xes/grooveboxes which you want to slave to that master
in that scenario, you can connect one cable from the master to the first x0xb0x (into the MIDI IN) and another cable from the THRU port on that x0xb0x going into the MIDI IN on the second x0xb0x
the THRU port is an output port! and the midi signal on it is a "copy" of the midi signal from the MIDI IN port, it doesn't pass thru the cpu at all, it doesn't even go to the mainboard.. the THRU port should work even if your cpu is dead and probably even if the mainboard is disconnected from the IO board

now, what that sentence really meant is, that the x0xb0x implementation of the "buffer" for the THRU port is not proper
it should ideally be a logic buffer, but (probably to simplify the circuit or to reduce costs) it's done with a transistor in a weird way
due to that, it has a side effect that it can behave as an input in certain situations.. but this is a side effect only
the intended role of the THRU port is to be an output

My problem looks the most like this post (except for the cause): viewtopic.php?f=12&t=21479
The helpful guest in this thread is suggesting to measure the resistance from the point where Q50 and R15 meet back to pin10 on the microcontroller, but I don't understand which microcontroller he is talking about.

he means the cpu (the atmega)
basically, with the x0xb0x not powered (switched OFF) measure for continuity (or measure the resistance) from that point on the IO board to the leg on the cpu.. the signal goes via the jumper cable J3 to the mainboard, and it's possible that it's not making contact for some reason

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Re: MIDI IN not working

by jorrit on Thu Nov 16, 2017 5:15 am

Antto, thank you for the explanation. I removed the sentence in my question, as it was just a side note and off-topic. MIDI THRU works as it should.

Even more thanks for the second reaction. I now understand that the maincontroller is the Atmega chip identified as IC3. So what I should test is the connection between Q50/R15 and pin 10 of IC3. I found out that it should be connected by wire 5 of jumper J3 (purple wire in my case). I resoldered this wire and now MIDI IN is working!

Problem solved. Thanks again.

jorrit
 
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Please be positive and constructive with your questions and comments.