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ASUS ASUS P5VDC-MX Dead CPU?

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    #61
    Re: ASUS ASUS P5VDC-MX Dead CPU?

    Originally posted by socketa View Post
    Which components would that be? Nearly all of the caps are FL and FJ and none of show signs of bloating
    Small ceramic caps that were part of the motherboard's design but were never installed by the manufacturer to save on costs. You can see many empty spots all over the board for those. And also for some 'lytics too. No telling if/when this corner-cutting can backfire.

    Also, just because they are not bulging or leaking doesn't mean that they are not bad... but given that they are Panasonic, we could be a lot more confident that they are probably okay.

    Originally posted by socketa View Post
    I went went back to the boards that i checked for the 8 pin 5V regulator, and found a GS78L05S regulator...
    Stuck a heatsink on it, booted the board, and then checked the chip input and output voltages with all 3 meters:
    Digitech : 11.78/5.02
    El Cheapo : 11.6/4.95
    Hioki : 11.75/5.00

    Looking at the datasheet, i see Min/Max range of 4.8V - 5.2V
    So hopefully this is verification that my meters are good enough.
    Yup, it is.

    So like I mentioned in my previous post, that means either something is wrong with that 7805 regulator on your P5VDC-MX or perhaps something downstream is shorted to a higher voltage rail, thus bringing the output high. Or just not enough caps on input/output of that 7805.

    Originally posted by socketa View Post
    When i first tested at the input pin, there was a spark at the probe lead, and a "pop" sound (ever got spark off of a multimeter probe when taking a voltage measurement?) - thought that i might have blown the chip, but it still booted into BIOS OK and the chip was still outputting 5V.
    Nope, not from my multimeter.

    I can only think of two things to cause this: mains wiring fault (lack of ground likely) or static discharge from your body.
    Make sure you touch something that is metal and grounded before working on your electronics. That should minimize static discharges. Also, check the ground at the plug where you had this incident happen. Shouldn't have too much of a potential difference (well, preferably none) from neutral - like a few volts at most.

    Originally posted by socketa View Post
    Could this spark produce an audible "pop" sound?
    Yes. If you can see a spark, many times you will be able to hear it too.

    Originally posted by socketa View Post
    So there is now two vacant MOSFET positions on the P5VDC-MX VRM area and they are in parallel with each other (i.e. a hard short from drain to drain and hard short from source to source)
    I am *guessing* from the area around the CPU (you didn't specify). In that case, do NOT run the board like that AT ALL. You could easily blow a VRM driver.

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