Microdot digits 1&2 usually dead

I have several microdot hats. One, that I soldered up today from a kit, has digits #1 & 2 dead. Actually those digits come up for a second and then go off, and I start getting “IO Error” in my python terminal output. Other microdot hats work fine. I don’t think I fried the controller chip for those digits (I’ve been soldering since circa 1978 and have reasonably good ESD-safe technique).
Any thoughts?
I’m just getting into the libraries for the microdot hats, and haven’t done a full code review, so let me ask, are there any diagnostic commands to probe the controller chips?

It’s using i2c so you could run sudo i2cdetect -y 1
You should get back 0x61, 0x62 and 0x63

  • 0x62: IS31FL3730
  • 0x63: IS31FL3730
  • 0x61: IS31FL3730
    It sounds like one of the 3 IS31FL3730 LED matrix driver chips is having an i2c issue. If I have it right each chip drives two digits / displays.