Merckaert Dimo

I checked the box and the circuit board I recieved is a 77087. I told them it was for a caldera Aspire and they send me this one. I check further the main board and see on the transistor a bit rust. Could this be the fault? When the hot tub is on, the transistor makes bit noise. ( video attached). Do this look normal? How can I check that the heater board works fine? Measuring voltage white and black cable from the heater? Thanks in advance!

Thx for your input @RDspaguy. @castletonia i really Hope you can help me along !

Hey, thanks for your input and reaction! I will try to check this tomorrow!

Hi everybody, I've got a problem with heating my hottub. I've already changed the heater ( electricity feeling in the water). Also the pressure switch to be sure. But still no heat. And still slighty electricity feeling in fingertops.. I've checked the heater relay board on black spots but that seems ok. No fault code on the topside panel. D17 light is on (main board). Now i bought a new main board but i Think they send me a wrong one. Any opinions? (Pics attached) Hope you guys can help me. Thanks in advance