F1 Blown on OSPi board, but no longer in schematic?

[davethomaspilot]

So, my OSPi died last fall. Just got around to taking it out of the waterproof enclosure and looking at the PCB.

Turns out there’s a fuse F1 that is blown. There’s no such part on the latest schematic, so I suspect it has been eliminated?

Should I just put a jumper in instead of the fuse and hope for the best? Or, can you provide a P/N I can use to replace the fuse? I have no issue removing the existing, open F1 with a heat gun and soldering a new one.

Thanks!

Dave Thomas

[davethomaspilot]

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!

[davethomaspilot]

replying just so I can check the box to get notified of follow up emails.

[davethomaspilot]

I opened a ticket on this, but still haven’t got an answer. So, I thought I’d try again here.

I ordered up both through hole and SMT versions of the fuses. Should I populate only one, or both? If just one, which one?

The reply I got from the ticket asked me to send a photo of the board. I replied with a photo of both and got a response that F2 was clearly blown on one of them. (That was pretty obvious).

The ticket also said to measure resistance across the supply nets to verify no other parts were shorted (that’s pretty obvious too). But, what I’m looking for:

1) Should both the SMT fuse and through hole be populated? Probably not, but the first board that failed had both populated.
2) Is a schematic available that matches these boards? (the schematics I’ve found show neither an SMT nor through hole fuse).

Dave Thomas

[davethomaspilot]

Looking at the picture of the board here:

https://opensprinkler.com/product/opensprinkler-pi/

I see neither an SMT nor through hole footprint for a fuse (F1?) on the board.

Maybe the fuse was eliminated entirely in the latest design? Maybe the reason was that a blown fuse that requires rework of the board to replace isn’t much value over having no fuse at all?

So, four choices, I guess:

1. Use jumper in the footprint for the through hole F1.
2. Use only the through hole fuse
3. Use only the SMT fuse (like the board that died last fall
4. Populate both (like the board with the burnt F2 that died over a year ago)

Can anyone help?

[Ray]

I think the issue has already been addressed through a support ticket. If not, please feel free to resort to support tickets.

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