MIDI does not work after case mount (solved)

Hello,
i am nearly frustrated. Got my Shruti mounted and tested so far. Everything worked fine: Audio, MIDI, LCD and so on. The beast roared fine…
Now that i have mounted the Shruthi to the case my MIDI in doesn’t work any more. Of course a part which is placed under the LCD…is there any kind of check i can do without desoldering the LCD panel ?
I would appreciate any kind of advice and thanks for your time in advance.

Check that pin 5 of the optocoupler is continuous with ground ; that pin 8 is at +5V ; and that pin 6 is at +5V and drops down when there is MIDI traffic.

OK, i will check that as soon as i can. Today is our company christmas dinner, so eventually it will take till tomorrow, but thanks so far.

The results so far:
PIN 5V continuitiy to GND
PIN 8 4.95V
PIN 6 4.95V without dropping down

Continuity between pin 6 of the optocoupler and pin 14 of the MCU?

Or maybe it’s a wrong MIDI channel problem?

Pin adressing is similar to the smaller IC ? Then yes continuity pin 6 to pin 14 MCU. Checked MIDI keyboard with my 909, set to channel 1 and works…so it’s not the keyboard.
Triple-checked MIDI channel set to 1 on the Shruthi ??? wtf is happening here ? set MIDI channel to 3 on keyboard and Shruthi - does not work either, so it is not a wrong channel problem. Checked this setting with another synth and it worked too.

Worse case scenario, it looks like i’ll have to desolder the LCD panel and check for weak solder joints of the MIDI connectors. facepalm.
And this after it frigging worked before…

the pins that count on the midi sockets are accessible from the flipside.

You mean i should try to solder them from the other side ? I guess this is worth a try before going through the pain with the LCD panel…

making a better connection means actually just reheating pad and component lead together and maybe apply a little bit of solder. as long as you can reach the contacts it should work

Sounds reasonable :wink:

Ok, tried it from the other side, nothing changed - i am going the hard way now. Its time for the solder sucker and solder wicket now .

have you measured pin to pin or just to the pads? could be a bad connection to the sockets also

I have made some pin soldered to a cable which i pushed into the socket benath the pins, so i think the measures can be trusted.
But i still don’t see the light, as it is not possible for me to desolder the LCD panel. I removed most of the solder but it does not lift from the pins.
What does really makes me mad, is the fact that is do not have a clue what happened while mounting the PCBs into the case, which might have damaged the solder joints.

So here is a status:
Measured all again with my second (much expensive and better than the other) multimeter PIN and socket .
PIN 5 continuity to GND
PIN 8 +4.9 V
PIN 6 +4.9 V no dropdown in voltage - ergo no MIDI
PIN 6 continuity to MCU PIN14
Soldered MIDI IN connector from flipside and it looks ok to me. Checked MIDI settings in Shruthi. Checked MIDI setup on two other synths and it worked flawless.
I can do anything with my baby, but not play it with my keyboard. I confess i am definetly clueless. Tried to get rid of the LCD panel, but my solder sucking pump does not remove all of the solder, so i did not get it loose. I won’t proceed any further today, because i want to avoid any kind of damage by impatience. Are there any suggestions or tips how to remove the LCD without killing it ? I am going to head for a bottle of whisky now . I am done.

it isn’t too easy to desolder, that’s true. i’ve done it a few times and have to do it again. what i do is going along all pins with the iron as flat as possible so i heat up more than one. or lay some desolder bra(i)d over the pins to spread the heat more. then when you start on the left again pull the left corner up while you move towards the center. same on the right. i had to do this a few times until it came off.
i always cut the headers off right on top of the lcd pads so there isn’t much travel.

Dang, i should have thought myself about cutting the pins. But i am still concerned about if this removal will help. I have no further idea where to search then, i just resoldered all resistors and the diode to be sure there ist nothing left i could have missed on the accessible side…

So, finally got the LCD panel off, resoldered every MIDI Connector pin and checked for continuitiy on the PCB - it works again !
Let’s see if this is still the case when panel is back in place, cause i don’t like the idea of doing this again.
By the way, while i was playing around i realized a hum at very low tones. Is it possible that something wrong with the filter board or is my wall-wart just crap ? It sounds like a classical 50 Hz power induced hum.

It might be that your wall-wart does not deliver enough current.

it should deliver 400 mA, but in the vast abyss of my memory i remember there should be a second one with 1A, maybe this will do it - if i can find it in this chaos here :wink:

F_ck yeah, i can even switch the programs from my keyboard and remote control the synthesis…hehe