I have not seen anything like this happen before. If the chip is in backwards, or shorted in certain ways, I could imagine this happening. We’d be happy to give you a replacement chip, but it’s critical to identify what caused the problem. If you cannot, then the same thing will most certainly happen again after you replace the chip.
It’s possible (but unlikely) that there’s an issue with the LED matrix itself. If so, it would be possible to test by swapping it out onto another Meggy Jr, to see if it works there. You can bring your unit by our shop during business hours, but it might be helpful to make an appointment (off-forum, please) to ensure that we’re expecting your visit.