MIDI Pin Issues

When making my case I reluctantly decided it was best to desolder the midi sockets from the PCBs for placement elsewhere. During the process I managed to damage one of the pin sockets. arrgggh. The socket eyelet came off of pin 4 of MIDI socket X1 (MIDI in) and the thin copper wire that, according to the BRD file, connects to the 220 resistor. I was able to affix the eyelet back to it’s hole, but the thin copper wire had come off the board and curled back away from the socket. I re-attached it to the solder blob connecting a braided, 20-gauge wire to the socket hoping that the copper wire would still function. I tested the unit by setting it to channel 0, turning off MIDI thru and connecting this socket to a midi keyboard. The small note character on the upper left of the LCD was visible every time I hit a note on the keyboard. I used ableton to control an undamaged CEM3379 successfully, but was unable to do the same with the above mentioned control board attached to the SM4 unit on any channel. I inspected the joint and the thin wire is still connected to the solder blob, and using the midi keyboard works fine. I’m not sure what could be wrong. I’m thinking that I may just bypass that small wire and attach the resistor to the solder blob. What is the X1 pin 4’s function? What do you guys think could be the issue? Is the 220 resistor the only connection to pin 4, or is there another one on the underside I’m overlooking?


A Quick look to the schematics show that pin 4 is only connected to the R220 R19 and nothing else. Pin 4s function is to connect the Shruthi Optocoupler to the MIDI-Cable :wink:

Thanks. I used a small wire to connect the 220 ohm resistor to pin 4 and everything works.