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Just finished attaching the PEEK fan on chapter 20 in the Rostock MAX assembly instructions. I had put connection points on my wires rather than just soldering them together, since I intend to change out the fans and hotend once I get this printer fully working and I wanted to make it easy to switch out the components.

I was thoughtless and didn't turn off the power before plugging in the fan. Now the display panel won't light up and I can no longer communicate with the board. I'm still getting a com port, so USB is still up, but nothing else is working. The fuse is intact. Did I brick the RAMBo board by plugging in the PEEK fan under power? The hotend was at room temperature, so the fan should not have been on.

What steps can I take to know for certain if the board is fried?

Did you check all the fuses?

There are some micro fuses there.

Plugging/unplugging the fan shouldn't have blown a fuse, even if it would've been receiving power at the time. Double-check your wiring to see what might've caused your problem.

Teoman got it right. Micro fuse F3 was blown. I'm not sure how that happened, I agree with Ben that it shouldn't have blown a fuse. I'll double check my wiring anyway.

Would current from the steppers blow that fuse if I were moving them too fast? I've been trying to avoid generating current through the steppers, but I may not have noticed pushing an arm when I was plugging in the fan.

Depends on your power supply. If you used a pc power supply, it can probably handle it. If you used an industrial power brick, I've heard those can be much less forgiving and can result in blown fuses from stepper currents.

Scratch that, you said the machine was running when this happened, in that case it should have been fine either way (I think...)

PeteD wrote:Teoman got it right. Micro fuse F3 was blown. I'm not sure how that happened, I agree with Ben that it shouldn't have blown a fuse. I'll double check my wiring anyway.

Would current from the steppers blow that fuse if I were moving them too fast? I've been trying to avoid generating current through the steppers, but I may not have noticed pushing an arm when I was plugging in the fan.

I've never seen a fuse blown from moving arms, including experiments I've run on axis drivers where i move axis by hand as fast as I can.
It's more likely something momentarily shorted when you unplugged or plugged in the fan.

The thing it's not safe to plug/unplug with power on is the motor connections, the drivers are extremely sensitive to over voltage and the act of unplugging/plugging in can result in a voltage spike that will blow them.