Do you happen to have any close up images of the soldering/electrical components you are referring to?
agreed. Picture of your soldering would help.
I've got a Tex Yoda from Massdrop, which I used for about a week before the trackpoint stick broke. 
The one at keycon broke too
I was able to get a replacement from Massdrop 
Heard the MOQ was high so they have a small stack of 'em. Massdrop is great.
but it didn't include the FPC connector necessary to swap it out directly.
probably came that way from the manufacturer
So I desoldered the connector from my busted module and soldered it to the new one. Now it behaves oddly and I have no idea how to go about debugging it. I've got access to Linux and Windows machines for USB testing but I'm not sure if there's electrical checks I can do first or how to do them.
That's the GH way!
Symptoms:
When first plugged in, the keyboard and trackpoint and mouse keys all behave as expected. There's some random movement in the trackpoint but that was true of the ones in my Thinkpads as well and I'm pretty sure that's calmed with driver tweaks in software. However, after a period of time (minimum 30 seconds, maximum two hours), usually around 40 minutes the trackpoint and mouse buttons will become non-responsive. Unplugging and re-inserting the USB cable from the machine temporarily resolves the issue sometimes, but it is not consistent.
The mouse buttons come in on a separate FPC connector so I'm confounded by the fact that they seem to stop working when the pointer does. What's the best way to try and identify the root cause here? Do I start with electrical or checks or is there some way to get data out of the driver.
Wow that is odd.
All I can think of offhand is the following:
1. IIRC the trackpad is PS/2 native, the USB hub onboard the yoda has a PS/2 to USB adapter for it before it heads into the USB hub.
Because of this, it could be "resetting" like PS2 to USB devices sometimes do.
What I think (just offhand) is that it could after warming up one of the lines breaks connection then the USB hub goes nuts and you need to replug the KB to get it working again.
Overall it seems to be an issue with the new trackpad module and/or the interface to the "mainboard" USB hub.
Another issue is possibly with sending / receiving pointer HID information from the device to the OS. It could be that the HID keyborad info is fine, but something in the TP module is causing something to happen and either the device freaks out or something on the device causes the OS to freak out and drop the pointing device information.
I guess you can check this by looking at devices (device manger / system profiler / various linux commands depending on OS) after the trackpad and buttons quit working. Other people like Grendel know a lot more about how USB devices work than I do.
I can't explicitly rope people in but I'm lookin' your way DorkVader to help me out with this <3<3<3
I'm touched <333
Anyway, let me see pictures!
