Hardware info to repair after electrical storm

[JimS]

Had an electrical storm here stronger than most and lost the OSPi. The Pi was damaged but the OSPi board seems ok. May have damaged the a/d converter – still need to check that. It did damage both my expansion modules – Several inputs are shorted to ground on both of them so will be replacing the ‘595 chips. And one 2.2 ohm resistor is blown away. I got some of the older schematics from the github site. Where are the docs for the expansion modules that include the 2.2ohm resistors? I see there are resistors on the inputs of the ‘595 on the main board but not on the expansion modules – seems like a small resistance there might be a good idea. In another message it was explained that the resistors were there to protect the pi ports but the resistors are only for the on board ‘595 and the pi ports are wired directly to the expansion connector so that explanation doesn’t seem to line up with the hardware implementation.

Also wondering about the 2.2 ohm resistors. I don’t know the exact specs but other resistors that size are rated about 1 W. Conservatively you should run them at 80% or lower so that’s 800 mW. That means slightly less than 400 mA. In the case of a short the current will be about 10A before it goes up in smoke and will kill the triac and resistor. So I am left to wonder what it’s there for as it doesn’t protect anything.

And what are the additional parts added where the transient suppressors are? It’s a spark gap or transient limiter of some sort.

I did have some network damage so will be making this use wifi. Well aware that all transients can’t be protected against so with long wires in the ground I may have to live with some damage on unusually strong storms.

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