How do I diagnose GPIO issues?

Question

I was soldering LEDs in an extended line the other day when I accidentally forgot to shut my Raspberry Pi 4 off. I continued to solder and soon enough shorted my Pi out. It rebooted quickly and all seemed fine except now none of my ~50 WS2812B LEDs will turn on. Here is a list of things I've tried to diagnose my issue:

1. Unplug and replug the 3 wires running to LEDs to see if I could turn them back on.
2. Solder a single LED and light it to see if I fried the LEDs on the previous string (didn't work).
3. Used a multimeter to make sure my wires didn't somehow disconnect (they haven't).
4. Used the multimeter to check that 5v and Ground still worked (they do).
5. Ran the gpiotest mentioned here: https://forums.raspberrypi.com/viewtopic.php?t=180505 (returns that all pins are fine)

The Pi seems to run perfectly fine apart from having no output to my LEDs. All of this leads me to believe that the problem is with my Pi, however, I can't tell what the problem is. I'm looking for ideas on what the problem could be as well as some guidance as to how I could diagnose this myself in the future. Thanks.

Answer 1

Welcome. Here is how I have been doing it for years. Use two LEDs connected parallel but in opposing directions or a two color two pin LED and resistor (300 - 500 Ohm range) in series. Connect to port pin the other end to ground or +3.3 it doesn't matter. Write some simple code to switch the pin from high to low at a slow rate like the blink program. Your Led(s) switch or change color. First test your setup by connecting 1 end to the 3.3V the other to ground and see which one lights up, then reverse the connections and the other should light. Happy testing.

Answer 2

You have not explained WHAT you connected to the Pi.

You claim to have done a number of things, but only vaguely define them. e.g "Solder a single LED and light it to see if I fried the LEDs on the previous string (didn't work)."

WHAT LED? how is connected? how did you test?

You claim to have run gpiotest (but not posted any output).
While joan's utility is worthwhile it doesn't actually test the external hardware.

I normally use my GPIOreadall for testing.
This, in conjunction with suitable programs, is a good testing tool.

You can use the inbuilt raspi-gpio to read pins raspi-gpio get 0-27 provides this in a slightly less readable form.

The following can test individual pins e.g this will set a pin as output and drive high.

raspi-gpio set 17 op
raspi-gpio set 17 dh

GPIO are not as fragile as often reported, and it is unlikely you have damaged the peripheral system, even if a couple of pins don't work.
Properly connected LEDs are a good indicator.

You can test pins with either a meter (safely connected with suitable du-pont cables) or perform loopback.

E.g. connecting GPIO17 to GPIO27 would enable you to test that you can toggle a pin and read the result.