Again DO NOT hot-swap (disconnect or reconnect while powered on) the connection between the BMCU and the printer.
Doing so may cause irreversible damage to both the BMCU and the printer.
Sadly, I lost one of my BMCUs and the printer's motherboard due to this mistake.
During a recent round of BMCU testing, I unfortunately forgot this crucial precaution.
I performed a hot-swap between the BMCU mainboard and the Molex 4-pin connector while the printer was powered on.
This issue is primarily related to the design of the Molex 4-pin connector used by Bambu Lab. Additionally, the BMCU mainboard lacks adequate protection against such incidents.
During a hot-swap, electrical arcing (tip discharge) may occur, causing 24V to be unintentionally applied to circuits designed for 3.3V operation. This overvoltage instantly damages the control chip and the printer's mainboard.
The official AMSL from Bambulab seems to have the same problem, a few users in China have experienced AMSL failures due to hot swaping.
This is a rare but real risk. the author is currently designing a new BMCU board with improved protection to prevent this failure mode.
Currently, the number of users affected by this issue is very small.
(In fact, I had hot-swapped many times before without issues and even doubted the importance of this warning... until this happened.)
If you have accidentally hot-swapped your BMCU before, don't panic — your system may still be fine. Just be aware of the risk and avoid doing it again in the future.
If you encounter this issue, follow the official Wiki diagnostic guide to check:
If you are an A1 user and your warranty has expired, and if you have made any purchases from me before, and you confirm that it is your AMS connection board that is damaged, you can get an A1 AMS connection board from me for free (shipping fee not included).
⚠️ DO NOT HOT-SWAP ⚠️