Ok, so now I’m really confused.
On the pcb, I found what looks like what might be an 1812 PTC between one pin of the 24VAC connector and D1. Nothing is shown on the schematic for a part there.
I checked with a DVM–that part is open. It also appears to be cracked at its midpoint. If it’s a PTC, it’s now open.
I have another OSPi board that died before I replaced it with this one. On that board, F2 was completely burned off the board and there was lots of charring in the F2 area of the PCB (which isn’t close to F1) I found that board, thinking I could check use the “F1 PTC” from that board. If it was indeed zero or very low resistance, it’s probably a PTC. I could use it to replace the bad one on the newer card.
But, in addition to the (maybe) PTC, the original failed card had a parallel fuse F1 populated. On the newer card, there are holes for the fuse exist, but there is not one populated. The silkscreen says F1, but there the holes for the part are empty.
So, it appears on the first card that failed due to F2 blowing had a fuse (F1) in parallel with a PTC at the 24VAC connector. The fuse F1 was not populated on the replacement PCB.
But, why would there ever be a PTC in parallel with a fuse? That seems crazy. Maybe the designer hadn’t decided whether to use a PTC or a fuse, so had a footprint on the pcb so that either could be used? And the first pcb had both populated by mistake?
And why are neither of those parts in the schematics?
Both cards say OSPi v1.42+ on their silkscreen.
It’s going to get expensive if I have to keep replacing the card every year or two, especially since I have four different OSPi’s spread across the property. Interestingly, the location of this OSPi is the only one that has failed, and it has failed twice now. But, maybe the second failure occured because F1 was missing?
The first time, the RPi was also damaged, but this time only the OSPi pcb seems to be damaged, maybe only the PTC is open.
Ray, if you read this, please help! What should I do to fix the card? Can you explain what you’re trying to do with F1 and the part that looks like a PTC?
Thanks!