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Tube🍂Time

so I pulled the MOSFET and tried to power it up, and it works!? I'll probably still find a replacement MOSFET to avoid excess stress on the other phases.
28 Apr 2023 at 22:13 | Open on mastodon.social
18 comments
Krishean Draconis replied to Tube🍂Time

@tubetime did you need to swap the cpu, or did it survive the overvoltage?

28 Apr 2023 at 22:15 | Open on mastodon.social
Tube🍂Time replied to Tube🍂Time

i'm really hoping that a simple FET replacement will get this thing going reliably. the motherboard is technically off the shelf (Adlink M-880-Nitro) but people want lots of money for them.

28 Apr 2023 at 22:20 | Open on mastodon.social
Dantali0n :arch: :i3: replied to Tube🍂Time

@tubetime seems a wonder it didn't die with that mosfet but maybe CPUs have features against mosfet latch up or the pmic detects it and shuts off

29 Apr 2023 at 7:37 | Open on fosstodon.org
Tube🍂Time replied to Tube🍂Time

the MOSFETs arrived. who knows if this will work...
but hope it does
4 May 2023 at 23:19 | Open on mastodon.social
Tube🍂Time replied to Tube🍂Time

well it boots but now the frame isn't detected. so there's something wrong with the PCI card, the cable, or the backplane itself.
5 May 2023 at 0:48 | Open on mastodon.social
Tube🍂Time replied to Tube🍂Time

BTW, this is why the CPU didn't fry--the multiphase buck controller (the ADP3168) has crowbar protection in case of a shorted high-side MOSFET!
5 May 2023 at 0:55 | Open on mastodon.social
Tube🍂Time replied to Tube🍂Time

so the sequence of events in this case went:
Buck MOSFET failed
Buck controller crowbarred
12V power supply went overcurrent and shut down
Sequencer CPLD detected that and shut everything else down.

5 May 2023 at 0:56 | Open on mastodon.social
Tube🍂Time replied to Tube🍂Time
Tube🍂Time replied to Tube🍂Time

well it's back up and running!
5 May 2023 at 2:20 | Open on mastodon.social
Tube🍂Time replied to Tube🍂Time

it would be nice to have a second probe cable. this is the less common 60-pin cable, not the stubbier 50-pin one used on the 1650 series. they're super hard to find for some reason.
5 May 2023 at 2:56 | Open on mastodon.social
Tube🍂Time replied to Tube🍂Time

thinking about the failure a bit more. here's the precise cause with a nice diagram. a high-side MOSFET failed in a short circuit, which would put 12V on the sensitive CPU core rail. however, the controller chip detected the overvoltage and turned on all the low side FETs (circled in green).
5 May 2023 at 3:00 | Open on mastodon.social
Andy replied to Tube🍂Time

@tubetime Do you know whe there are only three high-side FETs but six on the low side?

5 May 2023 at 3:09 | Open on infosec.exchange
Dantali0n :arch: :i3: replied to Tube🍂Time

@tubetime ah so the pmic did protect the CPU, as expected, nice to see that even in this era such protections where already in placw, can't even begin to imagine the complicity of a pmic powering a modern Intel or AMD CPU.

5 May 2023 at 5:30 | Open on fosstodon.org
pcbeard replied to Tube🍂Time

@tubetime I was making popcorn. Great troubleshooting!

30 Dec 2023 at 19:52 | Open on sfba.social
Foone🏳️‍⚧️ replied to Tube🍂Time
Darryl Ramm replied to Tube🍂Time
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