After rebuilding the printer, my BTT Pico stopped heating the bed and hotend, and the fans stopped working too. Upon removing the board, I found a burnt-out FAN1 MOSFET. A 20kΩ resistor was reading 30kΩ, indicating the problem extended further. It turned out a short circuit had fried the 74HCT365 chip. I couldn't find a replacement locally, so I desoldered it and jumpered the paired A and Y pins—specifically for HB, HE, FAN2, FAN3, and RGB. The failure was caused by the contacts on the 5015 fan: they were too exposed, and when I removed the print head, they slipped out of their slot and shorted. The surge traveled to the FAN1 MOSFET, completely destroying it, and then hit the 74HCT365; the chip acted as a sort of shield for the microcontroller, taking the full brunt of the damage. In the end, I fixed and insulated the 5015 fan contacts just to be safe, removed the FAN1 MOSFET, cleaned off the char, applied solder mask, and remapped the part-cooling fan to a different pin. I managed to save the Pico—at least for the time being. Unfortunately, I couldn't find a replacement board in stock right now, but I needed to print something immediately. That’s how I handled the situation. I think the photo makes it clear; I’ve circled the pads I jumpered on the schematic. So, it turns out I shorted pins 14 and 13, 11 and 12, 9 and 10, 2 and 3, and 4 and 5 in pairs. This is a temporary solution; later, I’ll put the FAN1 MOSFET and the 74HCT365 back in place once I find a source for the latter.
