Capacitor plague

Leaking Chhsi capacitors on a MSI 694D Pro motherboard.

The capacitor plague (also known as bad 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 as of 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. Although modern manufacturing techniques normally ensure they vent safely rather than explode, manufacturers have been known to omit the key safety features that allow this. (This has been a particular problem with the recent proliferation of "no name" brands from China. All of the components required for making electrolytic capacitors are available from specialist suppliers, but there is no guarantee that any particular manufacturer will actually make them properly).

A serious quality control problem is that good and poor quality electrolytic capacitors will often have identical electrical performance when newly fitted. Only extensive accelerated life testing involving abnormally high ripple currents and high operating temperatures can identify inferior components. This contrasts strongly with most electronic components which are much less subject to spontaneous failure after assembly.

Incidence

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 other manufacturers (see below). The Apple PowerPC line of the iMac G5 computers and some eMac computers' motherboards and power supplies were also affected.

A power supply unit with failed capacitors.

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.

Some early brands of surface mount aluminium electrolytic capacitors suffered from an apparently similar, but actually different problem involving electrolyte leakage. Surface mount soldering is usually achieved by first screen printing dabs of solder paste onto the printed circuit board, gluing the components into position, and then running the board assembly through a reflow oven to melt the solder. In an attempt to ensure more reliable soldering, some manufacturers increase the temperature of the reflow, which unknown to them, damages the rubber seals of the capacitors, causing them to dry out or start to leak after one or two years of operation. Compact equipment such as video camcorders are particularly affected by this problem, in most cases becoming uneconomical to repair.

Even some automobile electronic control units have been found to have the known brands of often-failing capacitors. However, computer components are by far the most commonly affected.

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 primarily being discussed on this article (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.)

Symptoms

Bulging capacitors

Failed Choyo capacitors which have leaked onto the motherboard.

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.

Note: the electrolyte is usually wet, not dry. Be careful not to confuse electrolyte leakage with the petroleum-based glue (e.g. Evo-Stik) that is sometimes used to secure the capacitors to the board. This glue is a sandy yellow colour but turns darker (towards black) with heat. A dark brown crust up the side of a capacitor is invariably glue, not electrolyte. A common effect is corrosion of component leads covered by the glue, leading to leakage current or open-circuit. The presence of black glue is a sure sign that the capacitor has overheated due either to internal failure or inadequate ventilation.

Failed Tayeh capacitors which have vented through their aluminium tops.

As the capacitor ages, its capacitance decreases while its equivalent series resistance (ESR) increases. When this happens, the capacitors no longer adequately serve their purpose of filtering 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, 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, or rebooting before it is completed
• Never starting the POST; fans spin but the system appears dead

This failed capacitor has exploded and blown its casing off.

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 are not doing their job.

In video equipment such as cameras, VCR's, DVD decks, switchers, televisions, and monitors, failed capacitors typically produce a number of abnormalities in picture quality. Most often, the picture may have "hum bars" which are alternating light and dark horizontal lines across the picture. With standard-definition NTSC pictures, it usually manifests itself as two hum bars in the picture, which correspond to 60 cycles, or twice the 30 fps frame rate of the picture. "Herringbone" distortion can also be seen too when higher frequencies are not filtered well. These are wavy vertical or jagged lines that appear on a picture that can sometimes move and shake. Some video equipment has been so affected by failing capacitors that the control circuits do not even function. For example, a VCR could appear to have a mechanical problem because it will not accept a tape, but because the power feeding the microprocessor is so dirty, the Microprocessor does not even function enough to recognize that a tape has been inserted.

In audio equipment, failed capacitor symptoms can be heard in the output of the speakers as either a 120 cycle hum, or some sort of whirring or buzzing in the output. This malfunction in sound equipment can sometimes be particularly vexing for a technician because the failure can sound like a bad cable or a bad ground. This leads the technician on a wild goose chase attempting to figure out where the bad connection is, but only after extensive troubleshooting, is the problem found to be within a piece of equipment itself.

The same troubleshooting challenges can await an automotive technician attempting to repair a poorly performing automobile too. A malfunctioning ECM with bad capacitors may illuminate the "SERVICE ENGINE" lamp and store a whole host of error codes in memory indicating malfunctioning components in the engine. The technician servicing the vehicle then goes after these mechanical problems in the engine, only to never solve what the ECM is reporting as malfunctioning. This issue has been known to cost the vehicle's owner considerable amounts of money if the technician is not aware of the electronic malfunctions in the ECM. ECM failures can also damage mechanical components as well, as the control of these mechanical components is not handled properly. The plague of bad transmissions in many Chrysler vehicles has even been traced back to failed capacitors in the transmission ECM.

Cause of the failing capacitors

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 was not 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 aluminium 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.

IEEE Spectrum covered the issue , and later estimated that the problem cost US$100 million to fix.

Failure analysis

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.

The second theory is that as the capacitance decreases and the ESR increases, the buck controller for the voltage regulator alters its operating conditions to try to compensate for what it interprets as an increased load.

Electronic power supplies normally produce a range of output voltages (+5V, +3V, +/-12V etc), but voltage feedback is usually only taken from one of these, the assumption being that if that rail is correctly regulated, other voltages coming from the same transformer will also be regulated. However if the output filter on the rail that regulation is taken from goes high resistance or open-circuit, the buck regulator interprets that as a higher load current and applies more power to the switching transformer to try to compensate. The result is often that the other supply rails with still-good output capacitors get over-driven, and they produce abnormally high output voltages, which can damage other components in the device. This often happens with cheap DVD players and similar equipment.

File:Dscn3622.png

Capacitors removed from a computer power supply were found to have dramatically less capacitance than their rated values.

A capacitor rated 2200 µF may experience a drop in capacity to as little as 75 µF. A 50% drop over its life may 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 may oscillate (sometimes wildly) to voltages above the absolute maximum ratings of the ICs to which the supply is connected.

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 or 12 volts depending on the motherboard) to be applied directly to the CPU, northbridge, RAM etc, causing an often catastrophic failure.

See also

• Equivalent series resistance
• Equivalent series inductance

External links

• [1] - Carey Holzman claims to be the first journalist to bring this issue to the public's attention and has worked with lawyers to bring settlements from major manufacturers.
• BadCaps — A repair site offering tutorials on proper soldering, repair services and replacement capacitors
• Capacitor Lab - Repair and bad capacitor information site
• Motherboard Capacitor Problem Blows Up — An article about capacitor failures
• Identification of Missing or Insufficient Electrolyte Constituents in Failed Aluminum Electrolytic Capacitors; Hilman and Helmold, CARTS 2004