Do you think the MOV caused the charring or is that additional component damage?
TLDR power surge make mini split go boom, idk what im doing. Should I fix this board or replace it?
Little run down of the who what and why of the situation.
Im a homeowner with 0 component level repair training. But with the power of google, Reddit, and YouTube I’m basically a pro. /s
This is a BH00N171B power board out of my Mitsubishi mxz sm48namhz outdoor heat pump unit.
My house experienced a power surge during a winter storm. After replacing a few small things around the house, I figured that was it. A few month later I tried to fire up my mini split system and none of the indoor wall units responded. After going around with a multi meter I saw none of them had power. So I went to the outdoor unit which seemed to operating fine at first. That lead me to check the branch box and after opening that up, I instantly saw the board was damaged by the surge. I called the installers and they said power surges aren’t covered by their, or Mitsubishis warranty so all repairs were out of pocket expenses. The quote for replacing the board in the branch box was 1500$. Instead of paying that ludicrous price I bought the board myself and put it in, and the branch box returned to life but the indoor units still wouldn’t turn on. After digging into them I realized all of those board were damaged too, blown fuses and weird little blue disks in all of them with lots of charring. That’s when I decided to dip my toes into some component level repair.
With the help of google I learned what movs were, and decided if they blew up so spectacularly that they must have done their job and the boards may be salvageable.
After replacing the MOVs and fuses in all 5 indoor units they powered on, but only for a few seconds before shutting themselves down. After running through service manuals and YouTube videos I determined they were short cycling because they weren’t getting refrigerant when calling for it.
This is where I realized how foolish I’ve been the whole time. I somehow and convinced myself that the power surge passed through the outdoor unit without causing damage. After closer inspection I realized the board control board I was looking at was fine, but the power boards (3 of them) all had blown movs and fuses. So here I am looking to do more component level repair and seeking advice.
The MOV is clearly toast, what is the the little box with the charred solder point? And is that resistor charred from the MOVs violent self removal or did that see surge current as well? Finally, do you think this board may have seen too much surge to be reliably repaired without testing each and every component on the board?