MIDI loopback on core failed

Testing/Troubleshooting
1

I’m getting sme problems with my core

  1. The PIC is alive, sends the upload request every 2 sec

  2. The LED on the input port flickers on MIDI IN events

  3. the MIDI DEBUG test1 - LED is lit but does not flicker on SysEx events sent to the core

  4. the loopback test - events are coming IN (checked with a led), but not coming out

    I noticed with my multimeter, that a MIDI event causes the meter to beep (diode test) on an event

    i checked the path and up until the optocoupler it’s the same beep, but after the optocoupler

    and on the PIC it’s silent, i dunno if this test should pass the MIDI events unaltered, or do they change

    in some way? i didn’t do the standalone optocoupler test cause i don’t really understand it

any help welocmed, thanks.

2

hi atom

have you checked that the optcoupler is oriented the right way?  i noticed on the schematic and with smashtv’s cores that the optcoupler is oriented in the opposite direction to the pic (i’m going by the direction of the orientation notch on the chips)

hope this helps

OrganGrinder

3

i did the optocoupler test, and

  1. after connecting the LED to to pins 26 and 32 of the PIC the diode lights up

  2. a connected the MIDI IN and OUT socket pins like on the diagram (led still on)

  3. i tried grounding the pin (COM input of my multimeter), the led still on

and i checked the optocoupler position, it’s ok (opposite to the PIC the dot of the PIC is

upper left and the opto is lower right)

4

Hello atom,

dunno if get your problem, but maybe it helps:

  1. if u get an upload request, you should upload MIOS and an application. To my understanding no loopback is active when there is just the bootloader active

  2. the flickering of the input LED seems perfectly right

  3. sorry, never heard of the MIDI DEBUG test1- LED  :-[

  4. is it because you want to build a Midibox Link (Linking multiple Cores)?. If so, you have to enable the link in the application you use (eg MB64) or - if you are writing your own app - implement the forwarding by yourself. See this example (forwarding CH1-events): http://www.ucapps.de/mios_c_forward_chn1.html

Regards,

Michael

5

the CORE is not getting anything on it’s INPUT, it’s sending but not receving (can’t upload

anything, instead of checksums i get upload requests on every sent data chunk)

the debug test1 is this http://www.ucapps.de/mbhp/mbhp_core_midiin_debug.gif

the loopback test is with the PIC off the socket and when the TX and RX are connected

so everything that comes in should go out (that’s not working).

6

just an update:

  1. the MIDI event goes on the input (the multimeter beeps on every event)

  2. it passes the diode D1 (beeps on both diode ends)

  3. the input pin of the optocoupler has the signal (when connected t the optocoupler pin, the meter beeps)

  4. when connected to the output of the optocoupler no beeps, the voltage between IC2::5 and IC2::8 is 5V

based on this ca i assume that the optocoupler is broken

(i’ve been playing around with the MIDI input polarity alot, trying to figure out witch is right

and someone on the forum wrote that wrong polarity can break the optocoupler)

7

There is an optocoupler test which allows you to check, if it is really broken:

Best Regards, Thorsten.

mbhp_core_opto_test.gif
mbhp_core_opto_test.gif639×333 35.8 KB

8

yeah that’s the only one i didn’t do cause i don’t have the spare

resistors and no vectorboard to attach it, but i’m on my way to the

store today to get that stuff and will test it, also i’ll get a couple

of spare optocouplers anyway.

thanks for the help, hope i’ll manage to get it working.

9

i got a new optocoupler and still no luck

what should i be reading on the optocouplers output ?

is there some way i can find out if it’s passing the MIDI messages

what does it do in practice ? i don’t know what to do now, maybe

i’m looking in the wrong place, and the optocoupler was ok anyway?

i’m kinda stuck i’d appritieate some practical advice on how to debug this problem

thanks.

10

Is this test working?

if not, you propably missed to solder a pin, or there is a short at the bottom of the PCB

Best Regards, Thorsten.

mbhp_core_extract_opto_test.gif
mbhp_core_extract_opto_test.gif801×501 31.6 KB

11

i’m sorry bad i’m very unsure if im reading the test schematic right

i tried drawing what i’m wiring, the led+res on the pic is connected to pins 26 and 31 like

i drew, and the pins of the MIDI i/o are shortened like above, the LED lights up

but does not turn off when i connect ground to the MIDI IN pin (the other one)

is this the right “diagram” for this test ?

(sorry for the childish drawings but i’m very “green” when it comes to electronics)

12

Your drawing looks correct, there is only one error, but I guess that you’ve considered this: the polarity of the LED is wrong.

When the LED is permanently on, it has the same effect like if the optocoupler is not in the socket (you can remove the opto in order to doublecheck this behaviour). This would identify again, that there is a connection problem (did you check the bottom of the PCB?)

And another hint: check the polarity of D1

Best Regards, Thorsten.

13

I still can’t get it to recieve MIDI, i took some pics of the board

(poor qulaity i need to get a good camera ad repost asap)

Front

Back

i tried the loopback test again and it failed, when i took the opto out of the socket

and connected the in and out pins of the the optocoupler the loopback was fine (only i had to connect the remaining MIDI pins with each other otherwise it would not work J12 M- to J13 M- were connected and pins 2 and 6 off the OPTO were connected). When i put the opto in the socket no go (i have +5V between pins 5 and 8 of the opto). I don’t know how to check the diode (if it’s not broken), i have a digital multimeter with a diode teseter but since i’m a complete n00b in diy electronics i don’t know what sould it be showing in both directions of the diode (any help here?).

14

When the ground of your tester is connected to the cathode (pin marked with the black line), and + with the anode, it should beep (or show the current draw if no accoustic signal is available). If you test it in the other direction, it should not “beep” (-> no current draw).

Unfortunately on your pictures the direction of the diode cannot be regognized, but I guess that you’ve already doublechecked this with my pictures?

In the last months, we had several users who reported problems with the MIDI interface of their mainboard. I noticed, that you haven’t mentioned yet, which kind of MIDI interface you are using…?

Best Regards, Thorsten.

15

I’m using MIDISport 4x4 with M-Audio, though i can use

  • M-Audio Ozonic

  • Echo Audiofire

  • onboard Asus interface

(the midisport is the simplest to use for me)

16

With the MIDIsport 4x4 (and 2x2) normaly no problems have to be expected - hardware & driver work very stable

Best Regards, Thorsten.

17

With the MIDIsport 4x4 (and 2x2) normaly no problems have to be expected - hardware & driver work very stable

For what it’s worth, I regularly use a MIDIsport 2x2 under Windows XP and OS X with my MIDIbox SID and it works very well. There isn’t much to say about it, really. The device just works.

-Steve

18

yeah i don’t think it’s the midi interface, that’s definetly something wrong with my core. just can’t figure out what (yet :)).

19

Tip of the day: did you ever check what happens when the two wires to the MIDI In socket are swapped?

Best Regards, Thorsten.

20

Tip of the day: did you ever check what happens when the two wires to the MIDI In socket are swapped?

Best Regards, Thorsten.

yea.  I did that mistake once on a midi out, the result was no (valid) signal to the next midi device (midi studio didn’t read a thing until the wires were setup correctly).  no reason to believe that if swapped on midi in that a valid signal is recieved (signal on the wrong wire).

OrganGrinder