PCB under resin tank mount

Anyone knows what this pcb is?
It has 4 LEDs on it and it is under the resin tank mount.

Thank you.

I’m guessing that’s the tank heater PCB. Not sure what the LED’s would be for though.

No, that’s not the heater. The heater it’s above.

Ah, ok. I’ve found a teardown of a Form 2 here, where they surmise that it might be for detecting laser power. I do know that the Form 2 does some kind of laser power check so that might be what this is for. If you scroll about 2/3rds the way down the page I’ve linked to you’ll find a couple of photos and the following text:

Immediately underneath the protective glass sheet is a U-shaped PCB which I can only assume is used for some kind of calibration. The PCB features five phtoodetectors; one mounted in “plain sight” of the laser, and four mounted in the far corners on the reverse side of the PCB, with the detectors facing into the PCB, such that the PCB is obscuring the photodetectors. A single, small pinhole located in the center of each detector allows light to fall onto the obscured photodetectors. However, the size of the pinhole and the dimensional tolerance of the PCB is probably too large for this to be an absolute calibration for the printer. My guess is this is probably used as more of a coarse diagnostic to confirm laser power and range of motion of the galvanometers.

In the past you could see the laser scanning the 3 photodiodes/transistors every layer. There was some discussion and I think it does not do it anymore every layer?

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