Original Apple II power supplies are remarkably durable, but many contain an aging component that has become notorious among vintage-computer collectors: the RIFA interference-suppression capacitor.
After several decades, the translucent case surrounding a RIFA capacitor can crack and allow moisture to enter. When the capacitor eventually fails, it may produce a loud pop, blow the power-supply fuse, and release a cloud of foul-smelling smoke.
Replacing the RIFA before it fails is a worthwhile preventive repair for an otherwise functioning Apple II power supply. This guide will walk you through identifying the original capacitor, ordering the correct modern replacement, removing the power supply, and installing the new component.
Scope of This Article
This article focuses only on identifying and replacing the original RIFA interference-suppression capacitor in an Apple II power supply.
A complete power-supply recap—replacing the electrolytic capacitors or performing a broader restoration—is outside the scope of today’s article. We will not be evaluating or replacing other components in the power supply. Our goal is simply to remove the failure-prone RIFA capacitor and install the correctly rated modern X2 replacement.
Important Safety Warning
Apple II power supplies connect directly to household AC power and contain potentially lethal voltage.
Internal capacitors may retain a dangerous electrical charge even after the computer has been turned off and unplugged. Never assume that an unplugged power supply is automatically safe to touch.
Only perform this repair if you are experienced with soldering and understand how to work safely around line-powered electronics. You must be able to identify the high-voltage section, measure stored voltage with a properly rated multimeter, and safely discharge the power supply before touching the circuit board.
If you are not comfortable doing this, have the RIFA replaced by an experienced electronics technician.
What Is a RIFA Capacitor?
RIFA manufactured a family of interference-suppression capacitors used in computers, test equipment, and other electronic devices.
In an Apple II power supply, the RIFA is installed across the incoming AC line and neutral. Its purpose is to reduce electrical interference entering or leaving the computer through the power cord. While an Apple II can technically still boot without this capacitor present, leaving it completely missing removes all line filtering—meaning the supply will pass high-frequency switching noise back into your home's AC line. Returning the power supply to its original specifications with a safe component is always the best practice.
The original capacitor is often easy to recognize. It usually has:
- A translucent yellow or amber rectangular case
- Two radial leads
- The name RIFA printed on the body
- A PME-series marking
- A capacitance value
- An AC voltage rating
- An X or X2 safety classification
Common markings might include:
- RIFA
- PME271
- 0.1 µF (or 100n)
- 250 VAC
- X2
The most visible sign of aging is a network of small cracks in the capacitor’s plastic case. A cracked RIFA may continue working for some time, but its condition will not improve. Eventually, moisture entering through the cracks will cause internal failure.
Why RIFA Capacitors Produce Smoke
Many original RIFA capacitors used a metallized-paper construction sealed inside a molded case. As the case ages and cracks, moisture reaches the internal paper dielectric. When the power supply is energized, the deteriorated capacitor begins conducting excessive current or internally arcing.
The resulting failure can produce:
- A sharp pop
- White or gray smoke
- A strong burnt-paper or electrical odor
- Residue around the failed capacitor
The smoke can be alarming, but the Apple II will generally survive the event. Preventive replacement avoids this unpleasant surprise and reduces the risk of acrid residue being deposited inside the power supply.
Not Every Apple II Power Supply Uses the Same RIFA
Apple used power supplies from more than one manufacturer, and those manufacturers produced multiple models and circuit-board revisions. Power supplies commonly found in Apple II systems include units made by Astec and Dynacomp.
Because designs shifted, you must inspect your specific board. For example, in the widely encountered Astec AA11040B power supply, the primary failure-prone RIFA across the AC line is designated as C1 and is rated at 0.1 µF.
Choosing the Correct Replacement
The RIFA used across the incoming AC line and neutral must be replaced with a modern Class X2 safety capacitor.
Do not use an ordinary film capacitor merely because it has the same capacitance or a high DC voltage rating. Standard film capacitors are not engineered to handle continuous line-voltage transients safely.
A proper replacement should have:
- The same capacitance as the original (e.g., 0.1 µF)
- A Class X2 safety rating
- An equal or higher AC voltage rating (such as 275 VAC or 305 VAC)
- Compatible lead spacing (measure the exact lead spacing of your original component, which is typically 15mm for a 0.1 µF unit)
- A body size that fits inside the enclosure
- Recognized safety-agency approvals
Understanding the Capacitance Markings
Older capacitors may show their values in microfarads µF or nanofarads nF
Common conversions include:
- 10 nF = 0.01 µF
- 47 nF = 0.047 µF
- 100 nF = 0.1 µF
- 220 nF = 0.22 µF
- 470 nF = 0.47 µF
Replace the RIFA with the exact capacitance printed on the original component.
Recommended Capacitor Manufacturers
For a safety component connected directly across household AC, use a traceable capacitor from a recognized manufacturer. Established manufacturers include:
- KEMET
- Vishay
- TDK / EPCOS
- WIMA
- Panasonic
Avoid unbranded capacitor assortments with incomplete or questionable specifications.
Where to Buy the Replacement Capacitor
Reliable electronics distributors include:
- DigiKey
- Mouser Electronics
- Newark
- Allied Electronics
Tools and Supplies Needed
You will need:
- Phillips screwdrivers
- Temperature-controlled soldering iron
- Electronics-grade solder
- Rosin flux
- Desoldering braid
- Solder sucker or desoldering pump
- Digital multimeter rated for the voltage being measured
- Needle-nose pliers
- Flush cutters
- Safety glasses
- Fume extractor or well-ventilated work area
- Isopropyl alcohol (90% or higher)
- Small cleaning brush
- Correct Class X2 replacement capacitor
- Camera or phone for documentation
Step 1: Unplug the Apple II
Turn off the Apple II and unplug its power cord from the wall outlet. Disconnect the monitor, disk drives, and other peripherals. Place the computer on a stable, nonconductive work surface with adequate lighting.
Remove the Apple II cover. Before disconnecting anything, it is always a good idea to photograph the power supply, its motherboard connector, and the surrounding wiring for reference during reassembly.
Step 2: Remove the Power Supply
Locate the power-supply cable connected to the Apple II motherboard. Disconnect the cable by gripping the plastic connector (and squeezing the prongs on either side) rather than pulling on the wires. Remove the screws holding the power supply to the Apple II chassis, then carefully lift the complete power-supply assembly out of the computer.
Step 3: Open the Power-Supply Enclosure
Leave the power supply unplugged on your bench. Remove the screws securing the metal power-supply cover.
(Note: While the vast majority of standard Astec and Dynacomp power supplies use standard Phillips screws, a few rare early revisions or third-party units may feature factory rivets. If you encounter rivets, they must be carefully drilled out using a small drill bit, though this is uncommon for standard retail configurations).
Step 4: Verify That the Power Supply Is Discharged
Before touching the circuit board, identify the large primary-side electrolytic capacitor and measure the voltage across its leads with a properly rated digital multimeter. The primary capacitor may hold a dangerous DC voltage even though the supply has been unplugged. Do not rely solely on the passage of time.
If stored voltage remains, use a proper capacitor-discharge tool. Measure the voltage again after discharging to confirm that it has fallen to a safe level. Do not continue unless you can positively verify that the supply is safe to handle.
Step 5: Locate the RIFA
The RIFA is found on the primary side near the incoming AC wiring, power switch, fuse, or line-filter section. Look for the translucent yellow or amber rectangular capacitor. It may have visible cracks running through the case.
Read and photograph the markings on the body. Record the capacitance, AC voltage rating, and lead spacing. Do not remove it until you have positively identified its value and ordered the correct replacement.
Step 6: Compare the Old and New Capacitors
Before soldering, compare the original RIFA with the replacement. Confirm that the capacitance is identical, the replacement is explicitly rated Class X2, and the AC voltage rating is equal to or greater than the original. X2 film capacitors are non-polarized, meaning they do not have positive and negative leads and can be installed in either direction.
Step 7: Access the Solder Joints
You will need to remove the circuit board from the metal enclosure to reach the underside. Before removing the board, document the location of every screw and the exact position of all ground connections. Avoid placing stress on the original wires. Keep all hardware organized for reassembly.
Step 8: Desolder the Original RIFA
Locate the two solder joints belonging to the RIFA on the bottom side of the circuit board. Apply a small amount of fresh solder and flux to each joint; adding fresh solder helps the older, oxidized solder melt and flow more easily.
Use desoldering braid or a solder sucker to remove the solder from the first lead, then repeat the process on the second lead. Alternate between the two leads until both move freely. Do not pull hard on the capacitor while solder remains in the holes, as excessive force can lift a copper pad or damage the circuit board. Once free, lift the RIFA out from the component side of the board.
Step 9: Clean the RIFA Location
Clean the area around the original capacitor with isopropyl alcohol and a small brush. Remove old flux, dust, loose fragments from the capacitor case, or residue left behind if the old RIFA had already failed. Make sure the circuit-board holes are clear enough to accept the leads of the replacement capacitor.
Step 10: Install the New X2 Capacitor
Insert the new capacitor through the original circuit-board holes. The capacitor should fit comfortably without forcing or sharply bending its leads. Position it so that the body does not touch the metal enclosure or any nearby high-heat components.
Solder the first lead, followed by the second. Use enough heat to create a clean, shiny solder joint, but do not heat the capacitor longer than necessary. Trim the excess leads on the bottom of the board using flush cutters.
Step 11: Inspect the Repair
Examine both solder joints under bright light or magnification. Check for complete solder coverage, solder bridges, or loose solder fragments inside the enclosure. Confirm once more that the installed part sits flat and has the correct technical ratings.
Step 12: Reassemble the Power Supply
Return the circuit board to its original position within the enclosure. Route the internal wiring exactly as it was before the repair, taking care that no wire is pinched beneath the cover. Reinstall and tighten the metal power-supply cover completely before proceeding. Never apply power to the unit with the cover removed.
Step 13: Reinstall the Power Supply
Place the fully enclosed power supply back into the Apple II chassis and secure it with its original mounting screws. Reconnect the 6-pin power harness to the motherboard, making certain that it is fully seated and properly oriented based on the photographs you took in Step 1. Check the inside of the computer for any loose screws or tools before continuing.
Step 14: Perform the Initial Power-On Test
Perform the first power test in a clear, well-ventilated workspace. Ensure the computer's outer plastic lid is off so you can see the motherboard, but verify that the power supply's metal enclosure is completely closed and screwed down tight.
Plug the power cord into the wall and flip the power switch on. Rather than probing any live electrical lines, simply look and listen for normal system behavior:
- The keyboard power light should immediately illuminate.
- The system should emit a single, familiar startup beep.
- Connected video should display the "Apple ][" screen.
Turn the power off immediately if you see smoke, notice any electrical arcing, hear an unusual buzzing or rapid clicking, or smell a burning odor.
When the repair has been completed correctly, the Apple II will boot normally with the new X2 capacitor quietly performing its interference-suppression function safely in the background.
Common Mistakes to Avoid
- Ordering the capacitor based only on the computer model: Apple II power supplies vary by manufacturer and revision. Inspect the original RIFA inside your specific unit before ordering parts.
- Installing an ordinary film capacitor: The replacement must be specifically certified as a Class X2 safety capacitor to handle alternating current line spikes safely.
- Using a capacitor with the wrong lead spacing: Forcing mismatched leads into the board puts unnecessary mechanical stress on the component pads. Measure the original lead spacing first.
- Pulling the RIFA before the solder is fully removed: This can lift the circuit-board traces or rip out the plated-through holes.
- Testing the power supply with its cover removed: The power-supply enclosure provides essential protection from dangerous mains voltage. Reinstall it completely before normal power-on testing.
When to Stop
Stop and consult an experienced technician if:
- You cannot identify the primary-side capacitor or verify that the supply is discharged.
- The circuit-board pads or traces are heavily discolored, burned, or damaged.
- The power-supply fuse blows immediately during testing.
- Smoke or arcing occurs after replacement.
There is no shame in stopping. Vintage computers are replaceable. You are not.
Final Thoughts
Replacing the RIFA capacitor is a focused, preventive repair that helps avoid one of the most memorable—and unpleasant—failures associated with original vintage electronics. By taking your time, selecting a high-quality modern X2 safety capacitor, and respecting the presence of high voltage, you can easily protect your Apple II for decades to come.
At VintageAppleComputers.com, we believe careful preventive maintenance is an important part of preserving original Apple hardware for collectors, hobbyists and future generations.