Freeplay Zero unresponsive

[Flavor]

To be honest, that solder job looks really good for your first attempt at soldering!

Using excess flux is actually better than not using enough. I'd just say that you would probably want to clean off the residue with some isopropyl alcohol and a rag or something.

I can't see your solder joints perfectly in the photo, but I wouldn't guess that you have any major problems there. There are some that look a bit more bulbous than the rest. If you heated them up, the solder may wick down into the through-hole a bit more. That could be helpful, but my feeling is that it isn't your problem.

If you say that you had similar problems when hooking the Pi up to your TV without the Freeplay Zero attached, then I'd wonder about the Pi even more. Here's what I'd probably try next, if you don't have another Pi Zero available. If you do, try that first.

1) If possible, get a new SD card and apply the Freeplay Zero SD image to it. If not, then re-apply the Freeplay Zero SD image to the current SD card. It would also be fine to use a normal RetroPie SD image for this test.
2) Detach the Pi Zero from the Freeplay Zero.
3) Hook up HDMI and a USB controller to the Pi Zero.
4) Hook up power to the Pi Zero.
5) Boot it up and play it a while. See how it goes.
If it goes well, continue...
6) Shut down the Pi and disconnect power.
7) Attach the Pi to the Freeplay Zero. Connect Power directly to the Pi Zero. It should boot up and work just like it did in step 5.
8) Report your findings here.