Identifying Electrolytic Capacitor Failure

If you’re encountering problems with your electronic drives, it stands to reason that the first place you should look is at your capacitors. Non-functioning or leaky electrolytic capacitors are the culprit in the majority of failed electronic drives that we regularly repair at the MSI authorized service center. Failed capacitors are also regularly found on the control boards next to critical electronic circuitry.

Your ability to identify this problem as early as possible may help lessen the severity of damage that a bad capacitor can inflict on your electronic circuitry and components.

To assist you in diagnosing a problem with your drive, here are a couple visual and performance clues that may indicate capacitor failures.

Visual Symptoms of Electrolytic Capacitor Failure

A visual inspection is an effective way to help determine if an electrolytic capacitor is defective. Look for these easy-to-spot symptoms:

1. Bulging or cracking of the vent on top of the capacitor. This problem occurs if the capacitor becomes pressurized, causing the vent seams to split, thereby releasing the pressurized gasses rather than exploding.

2. The capacitor sits crooked on P.C. board. This is usually due to the casing being pressurized and the bottom rubber insert pushing out of the casing.

3. Electrolyte leaking onto the P.C. board from the base of the capacitor or vented from the top. This will appear as an oily film or brownish substance coating nearby P.C. board real-estate and circuits. Leaking material is very corrosive and damaging to components and traces.
4. Capacitor casings are missing. This occurs when built up pressure exceeds the vent’s ability to effectively relieve it. Material from the exploded capacitor will most likely damage surrounding components and/or the P.C. board.

Electrical Symptoms

As capacitors begin to fail the rated capacitance decreases and the ESR (equivalent series resistance) usually increases. When this occurs, the capacitor loses it capability of filtering the direct current voltages for the associated circuit, resulting in an increase in the ripple voltage that the capacitor is supposed to filter out. The result can be power supply failures and system instability. Capacitors that loose their filtering capability can also cause further damage to associated circuitry.

Symptoms Usually Denote Irreversible Damage

It is very important to remember that even if you’ve identified any of the fore-mentioned symptoms, it’s highly possible that irreversible damage has already occurred to the P.C. board.

Motor Systems Inc. has found the average life expectancy of electrolytic capacitors to be seven years. If your equipment is of that vintage, it is highly recommended that you have it expertly maintained as soon as possible. It is also important to note the life expectancy depends on many factors such as, ambient temperatures, voltage levels, and duty cycles. Based on the conditions in which your equipment operates, your capacitor life could be less than the norm.