Measure the off resistance across the FET (source-drain) in the IRF7413s? At least to compare against the new ones you've already ordered before soldering replacements in?
From what you're saying I'd probably be blaming the MAX1631 actually. i.e. it's gone a bit mental and turned on both FETs resulting in essentially a dead short on the input supply.
Yeah, that does seem a bit more probable than two separate chips suddenly both going bad at the same time -- except I suppose if one of them did go bad, the MAX1631 would likely crank up the other one and try to fry both..
Mmm... okay, I just measured the two that were removed: one shows about 10.5 Ohms, whereas the other shows infinity (my meter only goes up to 2MO). Since they should be identical, this means that at least one of the two has gone bad.
Well, being the sort of person that I am, I decided not to wait for the Digikey and Maxim shipments later this week. I actually have another not-completely-dead player around -- a Mk2a -- and so I pinched one of the IRF7413s from that, to use along with the likely-good one (infinite resistance) from the dead Mk2.
The player now powers up and works perfectly!
So I guess the Maxim chip is more robust than I thought.
Once the Digikey shipment arrives tomorrow, I'll put one of it's new IRF7413s back onto the Mk2a board, to restore its former not-quite-dead status. It's useful for debugging and tracing circuitry.
The photo below shows the working Mk2.
And the
a.png link shows the relevant PSU components, for reference.
Cheers
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