[jan-jaap]

I had a prof back in university that used to say 'to measure is to know'. Don't assume things. Measure, simplify the problem, solve it.

The DS1780 doesn't have a stellar reputation, so I wouldn't assume it's flawless after 20 years. You're probably right about the short, though.

In my case, I've got several IO4's, several system controllers, and the different combinations result in different erratic behavior. Exactly what gives the Onyx it's well deserved reputation. There are measurement points on the boards, but they're not accessible when the card is in the cardcage and the system is live, so I installed wires:



This proved that the blame was on the system controller (environmental monitoring) and not the IO4. There are some test points on the system controller too, but not on the feedback pin of the regulator so I soldered a wire. More measurements, again narrowing down the source of the problem, and hopefully a solution. But that will be a post of it's own.