Identifying Bad Capacitors
Electrolytic capacitors are one of the few components used in game consoles & home computers that slowly change over time. This is considered normal, and depending on usage, quality of original parts, etc., replacement will probably be necessary at some point.
Certain hardware is prone to having outright defective capacitors. Defective capacitors tend to go out of tolerance quickly, leak, or sometimes explode. These systems should have their capacitors preemptively replaced to prevent damage to surrounding components and traces.
Bad Capacitors, Non-Electrolytic
Polystyrene and tantalum caps seem to be the other two types that can have problems in older gaming/computer hardware, although not with the frequency of electrolytic.
If you need to kill some time, read the Wikipedia "Types of Capacitors" article. That article can give you a good idea of what a suitable replacement or upgrade may be for a defective cap.
Identifying Bad Capacitors
Sometimes, bad caps can be identified by certain physical characteristics, including:
- Bulged appearance
- Domed tops
- Asymmetrical or stretched plastic jacket
- Fluid leaking
- Split vents
Symptoms of defective capacitors may include:
- Excessive noise in audio or video, including 60hz audio hum or rolling bars in video
- Scratchy, distorted, or missing audio
- Low contrast, blurry, or distorted LCD displays
- Intermittent or outright failure
Bad surface mount capacitors are not always easy to identify. Besides being smaller, they are constructed in a slightly different manner than leaded capacitors and typically mounted flush to the PCB. They tend to leak downward, and due to their flush mounting, the fluid will not be visible until a significant quantity has leaked out.
Read the guide on converting surface mounts caps to traditional leaded caps
Gallery of Bad Caps
The underside of a leaking surface mount cap (Turbo Express)
Solder on the negative lead of this surface mount cap appears shiny and normal, however the positive lead shows damage (Turbo Express)
Corrosive brown goo left behind by a leaking surface mount cap (Turbo Express)
Turbo Express cap failure is not limited to surface mount parts. In this photo, a leaded miniature capacitor CC800 has failed (controller PCB) (Turbo Express)
Turbo Express CC800 cap shown leaking through the controller PCB. What is startling about this picture is that there is no hole in the PCB under this cap. The electrolyte appears to have actually wicked between the VIAs and circuit fiberboard and weeped out underneath the copper layer.
"The Rocketship". An amusingly dramatic capacitor failure (Turbo_Grafx_CD-ROM_Dock, Analog PWB)
Visible leakage on top of the 100uf cap (Game Gear)
Damage to solder pads, weakened legs. Fresh solder blob in lower-left shows the start of repair. (Game Gear)
Exceptionally bad cap on SMAIN PCB (Sega PAC-S10)
Visible damage to solder resist layer - beware of solder bridging during repair (Sega PAC-S10)
Sega PAC-S10 sound PCB, post cleaning, showing trace damage from leakage.
Undoubtedly bad (AppleColor RGB Monitor A2M6014, C530)
Corroded left leg on this Sega CD SMD cap
Failed Astrocade tantalum cap (Photo courtesy Scott at Stardust Arcade)
Puffy Apple 2GS main filter cap from ASTEC Power Supply. May simply look this way by design.
Bad Commmodore 64 motherboard caps (Photo courtesy Dexx)