Notice: This page will be updated in the future to be more properly flushed-out.

Capacitors are an electrical component found on all sorts of hardware. Its job is to regulate power flow throughout the device, and they are very important parts of circuits that include them. If they aren't working, the device won't be either.


You may already be aware of the great "capacitor plague" of the early 2000s, when electrolytic capacitors failed rampantly in computer hardware due to poor formulation. This is nowhere near the only time period known to have crappy capacitors though, there are many others that are far more damaging.


Electro-what?

There are many different types of capacitors, each ranging in ability and lifetime. One of the most common types is called the "electrolytic" capacitor. The name references its design, as these capacitors actually have a liquid electrolyte fluid inside of them. This fluid is highly conductive, and it's what allows the capacitor to function. Due to this design, it also means that all electrolytic capacitors have a limited life, and they will all fail eventually. Capacitors have a lifetime rating, usually a few thousand hours, but this isn't a strict limit. They could work for longer, or even less in rare cases. The point is, they will die someday. Other types of capacitors, such as tantalums, ceramics, and polymers can also fail, but due to being "solid" (having no fluid inside), along with a bunch of other factors, they fail much more rarely.


Through-hole (Radial and Axial) vs. Surface Mount (SMD)

If you've looked into caps before, you'll have seen these terms before. They reference the method of which to attach the capacitor to the circuit board it's used on. Through-hole capacitors, as the name suggests, go through a hole that goes through the entire board. Surface mount (or SMD) capacitors are mounted to solder pads on one side of the board. This design saves a lot of space, so you'll see this design much more on small boards, or boards that require a low height clearence.


Catastrophic failure!

Capacitors can fail in several ways. Here's a list with an explaination on each one:

  1. Drying Out - This failure mode doesn't cause much damage. In this case, an electrolytic capacitor "dries out" and stops functioning. The hardware that depends on it may stop working, but it won't damage anything, allowing for an easy replacement.
  2. Venting - Electrolytic capacitors are designed with small vents on the top of the can. This allows the capacitor to safely vent out any gas buildup to avoid an explosion if they are (for example), sent way more power then they were designed to handle. A venting capacitor lets of a hissing noise and may smell bad.
  3. Bulging/Leaking from the vent - This failure mode was the most common type during the early 2000s capacitor plague. If a capacitor is seen bulging from the top, or if it's leaked a crusty orange substance from the top vents than it has failed. Due to leaking from the top, it is unlikely to damage the board it is attached to.
  4. Leaking electrolyte from the bottom - This is the most damaging failure mode. Common on surface mount capacitors, this method causes the electrolyte fluid to leak its way onto the board it's attached to. This fluid is conductive, so it will start off by causing all sorts of electrical mayhem around the board. If the wrong 2 connections are shorted together, the wrong voltage could be sent down the wrong area of the board, blowing out components. That isn't the worst of it though. This fluid is also corrosive! If left on a board over time, it will corrode away solder connections, pads, traces and vias, causing extensive damage. This is especially common in vintage Apple and Amiga computers, although plenty of other hardware, such as the Sega Game Gear are affected, as every early SMD electrolytic capacitor is affected by this. (More on this failure mode later)
  5. Shorting out - Many capacitors simply develop a dead short when they die. This will usually break whatever circuit they're connected to, but it isn't too difficult to figure out which cap is the bad one.
  6. Going open circuit - capacitors can simply go open circuit and quit working.
  7. Explosion! - Yes, capacitors can blow up. Electrolytics will go off real good if they're fed too much power, especially those without vents, but they don't fail in this way naturally. Tantalum caps on the other hand can and will. Tantalums are generally very reliable, but certain systems are known to have some bad caps that blow up. Early IBM PCs and clones are notorious for this. They usually short out instead of blowing, but they can. Don't worry! They aren't a fire risk, as they are very small, and everything inside a computer is going to be metal or plastic anyway. An even more notorious explosive example of exploding caps is the dreaded RIFA filter capacitor. These paper capacitors found in many power supplies from the 1970s-1990s will develop cracks over time, and eventually will blow up and release a lot of nasty smelling smoke. They usually don't damage anything though.


Symptoms of Bad Capacitors in vintage Macs

  1. First, you will notice the sound output begin to become quieter. Eventaully, it will stop working entirely.
  2. Next, the Mac may start to become unstable. you may start to experience crashes, "Sad Mac" crash screens, and other freezing issues.
  3. After this, starting up the Mac will become next to impossible. Most times you tyrn it on, you will get a "Sad Mac" crash screen.
  4. Eventually, you will get no display output and the computer will appear completely dead.


  5. Another big sign that you have leaking capacitors is a strong "dead fish" smell coming from the computer. This is the smell of the electrolyte that has leaked out of the capacitors. If you smell this smell, get the board out IMMEDIATELY and clean up the leaked electrolyte and remove the failed capacitors before they have a chance to corrode your board away.

This problem doesn't just prevent the board from starting up, it kills the board. As these capacitors fail, they begin to leak electrolyte. This electrolyte is highly conductive, which is what causes the instability as they start to fail. However, the fluid is also corrosive, so as it sits on the board, it will eat away at traces, chip legs, and other connections until the board is toast.

In order to fix this problem, you need to remove the old capacitors from the board, clean up the electrolyte with Isopropyl Alcohol, an ultrasonic cleaner, etc., repair any broken connections, and solder in new capacitors.

This is an extremely important repair to do, and anyone with one of these old Macs should address this problem as soon as possible. If left on the board too long, it may become virtually unrepairable. If you don't have the experience to recap one of these Macs, at least remove the old caps until you can get it to someone that can install new ones.



Page last updated (MM/DD/YYYY): 05/20/2024
Update Reason: links updated

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