Problems with dual Athlons

Bari Ari bari at
Wed Jul 31 11:43:59 PDT 2002

Steve Gaudet wrote:

>We have found that power supplies (both the power line itself and the
>switching power supply in the chassis) can make a difference on the
>2466's -- a marginal power supply is an invitation to 
>problems for sure
>on these beasties.  This is reflected in the completely outrageous
>observation that I have some nodes that will boot and run stably when
>plugged into certain receptacles on the power pole, but not other
>receptacles.  If I put a polarity/circuit tester on the receptacles,
>they pass.  If I check the line voltages, they are nominal (120+ VAC).
>If I plug any 2466 into them (I tried 3), it fails to POST.  If I move
>the plug two receptacles up on the same pole and same 
>circuit, it POSTS,
>installs, and works fine.  I haven't put an oscilloscope on the line
>when plugging it in, but I'm sure it would be fascinating to do so.
>I agree here, 400w+ is needed.  Tyan claims that on the 2466 it's not,
>however, if you look at AMD's site they don't support this conclusion.
>>Few things I'd look at memory and cooling.  The MP Athlons I feel must have
>>copper core heat sinks with excellent fan match up.  I noticed you didn't
>>mention the case.  If its a rackmount make sure there is adequate space
>>between the case cover and the fan.  If not this could be the problem.
One of the most often overlooked and misunderstood problems with PC 
power supplies is Transient Regulation or Dynamic Regulation. Many 
factors play into the transient response of PC AC/DC and onboard DC/DC 
power supplies; switching regulator frequency, component tolerances and 
the series resistance of power supply cables, connectors and PC board 

Motherboard and PC power supply manufacturers meet cost targets by using 
low-cost, low-ESR electrolytic capacitors. However, if manufacturers 
excessively reduce capacitor values and sizes, they encounter another 
problem. Capacitor life is much shorter for capacitors with a lower 
value and higher ESR. With lower capacitance, higher ESR, or both, the 
ac-current components that heat the input and output filter capacitors 
cause the capacitors to dissipate more power. As a capacitor's 
dissipation increases, its operating temperature rises. An electrolytic 
capacitor's life decreases with increasing temperature.

You can calculate the capacitor life using the formula below. Capacitor 
life depends on operating temperature, ESR, and ripple current:


L is the capacitor life in hours. For a capacitor rated at 105°C maximum 
operating temperature and at 5000 hours life at that temperature, 
TC=105°C and LC=5000. TMAX is the maximum temperature at which you 
operate the capacitor whose life you are calculating. Use the formula 
below for TCAPCASE, which establishes TMAX for the above equation. 
(These formulas apply to United Chemi-Con LXV-series capacitors.)


where AC is the capacitor surface area in inches squared; 
PCINC=ESRXIAC2; IAC=IOMAX/(2XN), where N is the number of input 
capacitors connected in parallel, and ESR is the equivalent series 
resistance of the capacitor at operating temperature and frequency; and 
TAMB is the ambient temperature.

The calculated life of the C1 input-filter capacitors at 50°C ambient 
temperature for United Chemi-Con LXV series capacitors is as follows:

Fully compliant circuit=63,000 hours, or approximately seven years; 
Mostly compliant circuit=25,000 hours, or approximately three years.

In today's computer market, a variety of inexpensive motherboards and 
power supplies is available that has dramatically smaller capacitors 
with less capacitance than those in the designs above. For some of these 
inexpensive boards and power supplies, we calculated the capacitor life 
to be approximately three months!

The problems on the other side of the power supplies are the AC power 
line are low power factor, harmonics caused by the large (or multiple in 
a cluster situation) AC/DC switching supplies and poor wiring 
installation or use of hardware store quality power strips. The static 
voltage and current may look fine or be installed to the latest NEC code 
but the dynamic properties of the AC power lines may be inadequate for a 

Bari Ari

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