Gregory's Serverwell it boots but now the frame isn't detected. so there's something wrong with the PCI card, the cable, or the backplane itself.
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 so the sequence of events in this case went: 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. 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).  @tubetime Do you know whe there are only three high-side FETs but six on the low side? @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.   |
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!