I've got a dead Mk2 unit here. When connected to +12V AC adapter, it measures about 5V across the 12V socket (ouch!). Something is internally shorted somewhere.

After much fussing about, removing/replacing components as I traced the power circuitry, I found two very hot F7413 chips. These are the two regulators for the +5V supply (2.5V each?), controlled by the Maxim MAX1631EAI chip.

Disconnecting the next stage from the chip outputs had no effect, so I desoldered the F7413 chips. +12V now measures +12V again, which is good, because it means there's no internal short in the PCB! But the 3.3V still measures approximately zero volts, which is weird.

So I've ordered "samples" of the MAX1631EAI chips from Maxim (Digikey doesn't stock them), and also some new F7413 chips from Digikey (# IRF7413-ND, $4.65/ea).

Unless Patrick or Hugo have better advice, my plan is to first replace just the F7413 chips with new ones, and if that still fails I'll swap out the MAX1631EAI chip as well.

Hopefully that'll do it. Everything downstream from there looks fine -- no big shorts that I can find -- rather easy to isolate it there, as that's where the red jumpers are located for cutting off the +3.3V and +5V.

Cheers