Now be honest. Did your heart skip when you flipped that board? LOL
I remember years ago in an old stone farmhouse with one of these cave type attics. Open the attic door and there was bat Sh$t EVERYWHERE. Turned right around and left. Told the customer to have it cleaned and get rid of the bats. I'm not getting sick from the crap or bit to service a unit.
I will believe that the government is broke when the welfare checks start bouncing!!
It was the problem lol. And yes it was a basement install. I have no idea nor did the homeowner as to how it got in the furnace as the doors were on it as well as having the filter in it. Also the board was mounted properly with the 1/2" or so standoffs. When I suspect a bad board I always look for burn marks etc on back of board was a little surprised to see this.