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LW1DSE > TECH 03.12.17 16:10l 226 Lines 12211 Bytes #999 (0) @ WW
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Subj: Capacitor Plague
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บ * Capacitor Plague * บ
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The capacitor plague (also known as bulging capacitors, bad
capacitors, bad caps, swollen caps or bloated capacitors) involved the common
premature failure of certain brands of electrolytic capacitors used in various
electronics equipment, and particularly in motherboards, video cards, compact
fluorescent lamp ballasts, and power supplies of personal computers. The first
flawed capacitors were seen in 1999, but most of the affected capacitors were
made in the early to mid 2000s, and while news of their failures (usually
after a few years of use) has forced most manufacturers to fix the defects,
some bad capacitors are still being sold or integrated into designs in early
2007.
An incorrect electrolyte formula within a faulty capacitor causes
the production of hydrogen gas, leading to bulging or deformation of the
capacitor's case, and eventual venting of the electrolyte. In rare cases,
faulty capacitors have even been reported to pop or explode forcefully.
Contents:
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1) Incidence
2) Symptoms
3) Cause of the failing capacitors
4) Failure analysis
1) Incidence:
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Faulty capacitors have been discovered in motherboards as old as
Socket 7 and have affected boards manufactured up to the present day. The
motherboard companies assembled and sold boards with faulty caps sourced from
many manufacturers. This is also not a phenomenon that is specific to PC based
equipment; the first release of the iMac G5 and some eMac computers were also
affected.
While capacitor plague largely affects desktop computer hardware,
this problem is by no means limited to that area. These capacitors can also
be found in some cameras, network switches, audio equipment, DVD players, and
a range of other devices. Even some automobile electronic control units have
been found to have these same brands of often-failing capacitors. However,
computer components are by far the most common location of these capacitors.
The fact that these failure-prone capacitors are still being used
has angered many people, especially in cases where a motherboard populated
mainly with high quality capacitors has one or two of the bad capacitors on
it, leading to accusations of planned obsolescence on the part of motherboard
manufacturers. Indeed, a strong case can be made that these capacitors (which
often fail in 6 months or less) are still being manufactured, and are still
being chosen over superior components by manufacturers to use in their
products.
As of May 2005, some evidence shows that the failing Nichicon
capacitors on the iMac, Intel, and Dell boards are due to a different problem
(capacitors overfilled with electrolyte) than the one discussed on this page
(faulty electrolyte formula). However, both the effects on the system and the
physical appearance of the capacitors are the same as the other failing
capacitors, as is how to identify them, and the required repair. (This
affects the HM and HN Series capacitors only.)
2) Symptoms:
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The most common method of identifying capacitors which have failed
because of bad electrolyte is visual inspection. Such a capacitor will show
one or more of these symptoms:
* Bulging of the vent on the top of the capacitor. (The 'vent' is the
impression stamped in the top of the can. The impression forms the seams of
the vent. It is designed so that if the capacitor becomes pressurized it
will split at the vent's seams relieving the pressure rather than making it
explode.)
* In the case of Dell Optiplex GX270s often a "Thermal Event" is displayed in
white on a black screen when rebooting.
* Sitting crooked on the circuit board as the bottom rubber plug is pushed
out Electrolyte (a crusty brown substance) leaked onto the motherboard from
the base of the capacitor.
* Venting from the top of the capacitor, visible as rust-like brown deposits,
or a visible hole in the vent.
As the capacitor ages, its capacitance decreases and its equivalent
series resistance (ESR) increases. When this happens, the capacitors no longer
adequately serve their purpose of filtering the high frequency ripple over the
direct current voltages on the motherboard, and system instability results.
Some common symptoms are:
* Not turning on all the time; having to hit reset or try turning the computer
on again;
* Instabilities: hangs, BSODs (Blue Screen of Death), kernel panics, etc.
especially when symptoms get progressively more frequent over time;
* CPU core voltage or other system voltages fluctuating or going out of range,
possibly with an increase in CPU temperature as the core voltage rises;
* Memory errors, especially ones that get more frequent with time;
* Spontaneous reboots.
In case of on-board video cards, unstable image in some video modes,
failing to complete the POST (Power On Self Test), or rebooting before it is
completed, never starting the POST, fans spin but the system appears dead...
Unlike the physical signs which are conclusive evidence the
capacitors are failing, many of the operational signs may be caused by other
factors, such as a failing power supply, dust clogging a fan, bad RAM, or
other hardware problems. Instability, once the operating system has loaded,
may indicate a software problem (such as some types of malware, poorly-written
device drivers or software), and not a hardware problem at all. If any of
these symptoms are experienced, removing the system's case and inspecting the
capacitors, especially those around the CPU, may immediately identify
capacitors as the cause. If there are no physical signs, an oscilloscope may
be used to examine the voltage on the capacitors, with excessive ripple
voltage being a sign the capacitors aren't doing their job.
3) Cause of the failing capacitors:
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In some cases, the root cause of the failing capacitors is
industrial espionage gone wrong. Several Taiwanese electrolyte manufacturers
began using a stolen formula that was incomplete, and lacked ingredients
needed to produce a stable capacitor. (An anti-corrosion ingredient wasn't
documented, reported in comp.risks).
When a faulty capacitor is charged, the water-based electrolyte
becomes unstable, and breaks down producing hydrogen gas. Since these types
of capacitors are sealed in an aluminum casing, the pressure builds up within
the capacitor until either the flat metal tops of the capacitor begins to
bend, or the rubber sealing plug is pushed down. Eventually the pressure
exceeds the strength of the metal casing and venting occurs, either by
blowing out the rubber bottom of the capacitor, or bursting the scored metal
vent on the top of the capacitor. When an electrolytic capacitor bursts,
effects can range from a pop and a hissing noise to a small explosion.
Venting is typically messy, and the acidic electrolyte must be cleaned off
the motherboard to prevent further damage. (In some industrial SMPS and
motherboards, it has been saw to corrode tracks and pads of the printed
circuit board, and some components as IC's, transistors, and resistors)
IEEE Spectrum covered the issue, and later estimated that the
problem cost US$100 million to fix.
As reported in IEEE Spectrum Online, apparently a scientist stole
an electrolyte formula from his employer in Japan and left the company.
Shortly afterwards, this scientist took up with a Taiwanese electronics
manufacturer and used the formula there, then went on to sell the formula to
other firms. The problem was, the formula was wrong.
Missing were a few crucial elements in the chemical concoction
that made up the electrolyte inside the capacitor. Without these additives,
according to Dennis Zogbi of Passive Component Industry magazine, inside the
capacitor will generate hydrogen gas and burst after a short operational
lifetime. Burst capacitors will leak electrolyte onto the motherboard,
creating all sorts of electrical and chemical havoc.
Thus far, only Abit has come forward and stated that its capacitors
have been faulty, although it is widely believed that many other motherboard
manufacturers have purchased capacitors from the same component manufacturers
as Abit. IBM admitted to using some of the Abit motherboards in its PCs.
IEEE Spectrum has some great detail on this story. Corporate
scandals, boycotts, and government cover-ups can all be found within.
4) Failure analysis:
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While failing capacitors typically result in the aforementioned
system instabilities, occasionally, failed capacitors will lead to a failure
of the voltage regulators on the motherboard. There are two common theories
on why this happens:
The first (and simpler) theory is that the failing capacitors
develop a very high leakage current, overloading the voltage regulators and
causing them to overheat (in some cases, the unit becomes short circuit).
The second theory is that as the capacitance decreases and the ESR
increases, the buck controller for the voltage regulator increases the
pulse width (in a PWM circuit) attempting to compensate for the load, drawing
more current from the input and increasing the temperature in the unit. Since
most of the MOSFET's heat output is produced during the on time and switching
transitions, the increased current causes them to more overheating. This
effect is cummulative, and acts like a snow ball.
Some capacitors removed from a switching power supply were found to
have dramatically less capacitance than their rated values. A capacitor rated
2200 ๆF may experience a drop in capacity to as little as 75 ๆF. A 50% drop
over its life maybe to be expected, but not to 5% of its original value. The
stability of the buck switching regulator is compromised by such a dramatic
drop and the regulator's voltage oscillates (perhaps wildly) to voltages
above the absolute maximum ratings of the ICs to which the supply is
connected. There were some cases in which some of them are short circiuted,
causing a destroy of the power semiconductors and main supplies. Many times,
the MOSFET's temperaure is so high as it's soldering material (a mix of tin
and plumb) melts (obout 240 ๘C), and the piece fall, causing an interrupt of
the circuit, making it absolutely inoperative.
The most common failure mode of the voltage regulator is for the
MOSFET to fail in a way that produces a direct connection between the source
and drain, causing the system's power supply (5 volts on the motherboard) to
be applied directly to the CPU, northbridge, RAM, or other components
(normally working at 2.2 to 3.3 VDC, causing a 100% overload). This, in turn,
causes those parts to catastrophically fail. A motherboard with symptoms of
failing capacitors should be taken out of service until it is repaired in
order to prevent further damage.
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บ Compilled from various sources in the Intenet. Translatted to ASCII by บ
บ LW1DSE Osvaldo F. Zappacosta. Banfield, Buenos Aires, Argentina. บ
บ Made with MSDOS 7.10's Text Editor (edit.com) in a AMD's 80486. บ
บ November 15, 2007 บ
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