CPU rapidly heating up

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Hello,

Given my profession I've fixed a lot of computers to date, but this one
baffles me.

I have a computer with an AMD Athlon 64 4600+ (2.5 GHz, 65 nm I think).
After power on the CPU heats up rapidly coming from room temperature
(25C) to emergency shutdown temp (around 80C) in under 20 minutes,
rising quickly and beginning to level off at the top.

For those of you unfamiliar with this model of CPU, I have another one
exactly like it, same age and model in the same model of motherboard,
same original AMD heatsink, etc in a home server, which has sat at 2 C
above room temperature for it's entire life -- this is not a hot CPU!

The thing is, there is nothing wrong with the heatsink -- as far as I
can tell by feeling it is at the same temperature as the display in the
BIOS dialog, with maybe about 5C of lag (50C feels burning, etc, I do
have some experience in feeling the temperature). The fan works full
speed and there is no dust in the heatsink. I don't understand.

I can only assume that some sort of malfunction is causing the CPU to
generate much more heat than it should. But I don't even know what to
try to replace. Some kind of shortcircuit in the CPU? Malfunction in the
motherboard causing it to overclock the CPU? PSU? As far as I can tell,
the power ratings in the BIOS are spot-on (not perfect but right where
they should be).

I have considered maybe it's the outdated BIOS treating the CPU wrong
(it has happened before), however this same configuration once worked I
am reluctant to think such a problem would spontaneously surface over time.

Any ideas?

LP,
Jure

Re: CPU rapidly heating up

Jure Sah wrote:
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There are a few possibilities.

1) Thermal diode isn't measuring temperature properly.

2) Silicon die damaged, and Vcore power is shorting to ground.

    Stick a clamp-on DC ammeter around the ATX12V yellow wires and measure
    the current. If you repair a lot of PCs, a clamp-on DC ammeter makes
    a nice addition, to the regular multimeter for checking voltages.
    A regular multimeter, is a nuisance for making current readings, while
    a clamp-on DC ammeter allows the whole PC to be measured in a couple
    minutes (as long as the main power cable isn't sleeved). If the main
    cable is sleeved, you can stick an unsleeved ATX extension cable in
    place, to complete a main cable measurement. A clamp-on DC ammeter works
    via the magnetic field around the wire, and is also capable of adding
    the currents of multiple wires. You can take four red wires and stick them
    all within the jaws of the meter at the same time, to get a total reading.

    http://www.outsidesupply.com/ProductImages/380941.jpg

3) When a processor has a metal lid, it doesn't just lightly touch
    the top of the silicon die. It can either have some thermal interface
    material, between the lid and the die. Or in some cases, they use
    low temperature solder for a mechanical connection.

    (Core2 Quad with low temp solder removed - lapped with 2000 grit)
    
http://img145.imageshack.us/img145/8253/cpusenzaihs006ck6.jpg

    (Athlon64 with TIM exposed)
    
http://img48.imageshack.us/img48/9752/ihsremovedcacae3500zc2.jpg

    If the thermal interface solution is not working properly, the
    silicon die becomes insulated, and the temperature shoots up
    rapidly until THERMTRIP is triggered.

You should check CPU input frequency, multiplier setting, Vcore
setting, as possible reasons for increased power consumption. The 12V
current flow measurement, is to confirm the overheat is due to power
dissipation. If the 12V measurement is "normal" and under TDP, then
it could be a TIM (thermal interface material) issue between the
silicon die and the lid.

HTH,
      Paul

Re: CPU rapidly heating up


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Good job there with your very meticulous explanation and even on what
to look for to remedy the issue as well.

However, Jure...

My suggestion, DUMP the CPU and get yourself a newer one as they are
cheap enough now a days... better yet, upgrade to a real CPU... Intel.
LOL is the way to go.

I stopped supporting AMD machines many moons ago and I am not sorry to
turn away clients with their PC issues but once I know they got a AMD?
HA! Sorry pal...


-DNO

Re: CPU rapidly heating up

Dizz Nutts O'mine wrote:
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Idiot

--
SteveH



Re: CPU rapidly heating up

On Fri, 19 Aug 2011 11:31:47 +0100, "SteveH"

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DUMBASS!

-DNO

Re: CPU rapidly heating up

Quoted text here. Click to load it

No pro is going to turn away a good proportion of customers and
potential income on such flimsy grounds, that essentially amount
to advocacy rather than anything of substance.  If anyone actually
did do that that would be reason enough to give them a wide berth.
Support is about getting people's machines to do what they want,
not pontificating about what they should have bought.

--
Andrew Smallshaw
andrews@sdf.lonestar.org

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