Replacing capacitors
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| Guide details | |
|---|---|
| Topic | Skill |
| Applies to | Both |
| Difficulty | Medium |
| How often | — |
| Tools needed | Soldering iron Desoldering braid or solder sucker Flux Flush cutters Multimeter Replacement capacitors or cap kit |
Electrolytic capacitors dry out with age. Replacing them ("recapping") is one of the most common fixes for old monitors and power supplies. Kits with every capacitor for a specific monitor chassis are widely available.
First: read CRT monitor safety and Mains power safety. Large capacitors can hold a dangerous charge.
Signs of bad capacitors
- Bulging or domed tops, or leaking crusty residue
- Monitors with wavy, shrinking, dim, or unstable pictures
- Power supplies with low or noisy voltages
Many bad capacitors look perfectly normal, which is why people replace them as a set.
Matching a replacement
- Capacitance (µF): same value.
- Voltage: same or higher. Never lower.
- Temperature: 105 °C rated caps last longer than 85 °C.
- Type: match special types exactly. Some are non-polarized (marked NP or BP) and must be replaced with the same kind.
- Size: make sure it fits the space and the hole spacing.
Polarity matters
Most electrolytic capacitors are polarized. The side with a stripe (often with minus signs) is negative. The board usually marks the + hole or shades the negative side. Installing one backward can make it pop or burst.
Steps
- Unplug the machine and wait. For monitors, discharge the tube first. See CRT monitor safety.
- Take clear photos of the board, showing every capacitor's position and stripe direction.
- Replace one capacitor at a time so you can't mix up positions.
- Remove the old one. See Desoldering.
- Insert the new one with the correct polarity, solder it (Soldering basics), and trim the leads.
- Check each one against your photos before moving to the next.
- When done, inspect the whole board for solder bridges and cold joints before powering up.