Here are the pictures:
Full board:
board.jpeg
Power section detail:
detail.jpeg
now, after several tests, I would suggest not to tap one of the DC input PSU's connectors (the white ones). Even though it supplies 24VDC with more than enough current to power bith the board and the fan, these 2 inputs are isolated against each other, meaning that if you have conected your fan to input one and it fails, then your fan will stop working even if PSU2 is still supplying the board.
I found 2 viable options where you can connect a fan:
1) next to the DC input 2 connector, below the C105 cap you have 2 tap points (just above the D100 diode). These taps provide 24VDC no matter if PSU1 or PSU2 is powering the board. (+ is on the connector side, so on the right). Careful however: if you power your board throuch PoE, you will see +48V on those pins!! So basically, these pins have the voltage of the highest voltage of any of the board's active power supplies. So you should use this solution ONLY if you power your board via the built-in power supplies OR PoE OR Telco 48V. BE CAREFUL!!
2) probably the best solution (but I didn't test it yet because I don't have such fans at hand) is to tap of the voltage on the pads C113 next on the top right cornet of the transformer. These pins have a 5VDC output no matter what the board's supply is. this is the main 5V voltage bus of the board, which is filtered via the gray/pink cap just next to it, and also re-regulated to various specific voltages on many other places on the board. Be careful however, I would aim for a 5V fan with the smallest wattage, just to be on the safe side and avoid any possible disturbances.
I have ordered a couple of 5V 30mm x 30mm x 10mm fans (6mm thick fans would be even better) and will report when I have it working...
Disclaimer: If you damage your board, hurt yourself or kill your dog, it's your fault, not mine!
If you open up the enclosure, you agree to take full responsibility for anything that might happen including injury, death, or even a pink dinosaur knocking down your front door and eating your family. Remember that if Mikrotik sells the device without fans, it means that it doesn't need any fan! And these boards are installed all around the world and seem to be running fine without any fan!
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