Mike Shoemaker and I examined the brain this morning for clues about what went wrong on Oct 4th. Almost immediately we found that one of the two fuses was blown.
How this could have happened: there is a "screw-down block" at the top of the brain on one side with "+12V" terminals arrayed on one side in red and "Ground" terminals on the other side in black. We think something touched this block in a way that completed the circuit and blew one of the two fuses. In my opinion the most likely cause was the windbird plug, which includes one unshielded wire that acts as the instrument's ground. This wire was originally wrapped in electrical tape but I had to expose everything on that that last visit (Saturday, August 27th) to rewire the plugs for the windbird because it wasn't working properly, and evidently I did not rewrap it before leaving. Then on Oct 4th, David must have shifted the tangle of wires enough to short-circuit that board in the moments before he powered off the station with the on/off switch. It could have been shorted by other things during that Oct 4th visit (a little seawater, a screwdriver, other metal tools) but the windbird-plug explanation is plausible.
The effect: with the whole drill-down block powerless, none of the electronics would have had power -- not the brain, not the modem, not the radio, and none of the instruments (including the PacIOOS CTD). When the power switch was turned back on again, the only working part would have been the batteries, the charger-controller (with a red light to indicate charging), and the solar panels. So we think that the station continued to charge its batteries every day until brain removal in January but nothing else was working during that time (except the PacIOOS CTD, running off its own battery power).
What comes next: Shoemaker has the brain in his lab and will be checking it over for (other) signs of trouble. We will be wrapping that windbird plug in tape again, and Shoemaker has a plan to cover that screw-down block with some kind of shield to avoid any repeat of this problem. When he's done I will update the programming (to the latest version and put this brain on our lab's roof with some surface instruments. This should confirm that the electronics are all operational and that the charger-controller can still charge a battery. I'll let that run for a few days and then we'll box up the brain and ship it back to Saipan again. We'll be sure to ship spare fuses back to Saipan as well.
Mike J+