•Open IPMC rev 1.1 modules work fine

•Open IPMC rev 1.2 modules lead to fans speeding up to max speed

•Happens when the board is plugged in

•Fans may or may not slow down when board is removed

•IPMC rev 1.2 runs the same firmware as rev 1.1

•Reproduced by Rui with SM rev 2

•Not confirmed by Serenity team – but they use different firmware

•Tracked this down to the I2C buffers

•Rev 1.1 uses older parts: LTC4300

•Rev 1.2 uses newer pin-compatible replacement: LTC4307

•Replacing buffers with LTC4300 on rev 1.2 fixed the issue

•Current plan: use LTC4300 on rev 1.2 IPMC modules

• Unless we discover a firmware issue that leads to this problem.