If you, like me make 40 pin connectors for use with zynths then tend to believe them to be the villain before your own soldering.
I’ve been building zynthian-alm. It’s an Audio Injector zynth with 4 encoders built on veroboard and hard-wired to the PI 1/0 pins all put together in an nice Aluminium box which out-performs the plastic boxes from the heat point of view . . …
(Mofo if you think you have case problems feel for the case makers of this thing, now withdrawn from Amazon…).
It’s launch was considerably delayed by the failure of the select encoder to scroll in lists ( if you didn’t want to have an encoder fail that is the one you’d choose last so of course…).
Well after considerable debugging, resoldering and part swapping the faultly part was the 40 pin edge connector, apply a little pressure on the top of the connector and all came good, but I suspect it was probably the socket might have become damaged by constantly putting wires in to the connector to check continuity. In effect the metal was only making a connection when the whole housing was slightly warped.
Fix, replace connector (they tend to be cheaper in 10’s).
This machine is going down the pub next Wednesday to see if it can last a set as 12 string guitae input with a side order of midi keyboard…
Just added a little echo into the second channel as an effect . . .
All nicely stored as a snapshot for instant recall off the upper right encoder but maybe not on Warren Zevon… 
The correct pin as at 12/09/2024 are . . .
25,26,4, 0
27,21,3,7
23,16,2,22
Just running the whole thing off a USB battery pack ( well not the hdmi monitor)
and the MIDI in works!!
But, oh! It is you Wyleu! 
