[weblacky]

A little advice, don't bother trying to detect which of the DS1780 chips is malfunctioning and replace all three of them. I have personally seen completely shorted DS1780 dragging down the i2c bus, I have personally seen DS1780 with slightly damaged inputs giving slightly incorrect results only for a specific voltage and/or a fan RPM (while showing no other signs of malfunction), I have seen totally absent DS1780 chips shorted open where the bus cannot find them as if they had been removed. Replacement is faster than troubleshooting and preferred as slight damage can go unnoticed as you've seen.

DS1780 where the inputs are slightly off is the rarest I have seen but I have seen it twice in my life. Once here: http://forums.irixnet.org/thread-3238-po...l#pid23284

I have an unpopular theory as to what's damaging the chips but suffice it to say that the chip inputs have little to no protection from overvoltage or momentary overvoltage due to ripple this is also true of its power input. The data sheet specifically says that it should not be given voltage higher than 5.75v. These later SGI designs runs this 5V for these sensors directly from the power supply 5 V rail. Usually part of it standby 5 V ability as well. There is no VRM's and very little filtering in the way (on Fuel this is true, likely on O350, it's true...may not be true on Tezro. I've not looked but likely not due to low DS1780 Tezro failures). The only filtering I've ever encountered so far is a resistor series network that provides some amount of current limiting around the inputs of the DS1780 on fuel main board as well as fuel PIMM and fuel graphics cards.

Yes I'm aware that DS1780 ICs are $6-$7 USD a piece unless you buy a large quantity. You're just going have to bite that bullet and consider yourself lucky you don't have like a ton of them in a rack where you have to do the chip replacement on all of them.