The model name lied about the chipset
PREHISTORY
This one goes back to before Atlas, when I was writing Probe286, some bare-metal diagnostics for the PB686 because it kept failing POST on its timer now and then. I'd found the PB686 in the Micro House Encyclopedia of Main Boards from 1992, and it said the chipset was Chips and Technologies. Then I actually looked at my board, and the chips say Texas Instruments.
The jumpers didn't match either. My board has a whole bunch of jumpers that the Micro House diagram doesn't show at all. It turns out Packard Bell sold different boards under the same model name. I wrote it down as a finding with a rule I still follow: a document you found by model name describes some version of that model, and you check it against the board in front of you before you trust it.
The funny part came ten days later, when a research agent found the same Micro House entry online and reported the chipset mix-up as a brand new discovery. My note had been sitting there the whole time.
