Atari 800XL Capacitor Replacement Guide
Replacing the electrolytic capacitors in your Atari 800XL is a vital preventative measure to ensure stable operation, crisp video output, and long-term reliability. Decades-old capacitors can cause power instability, random crashes, faint or distorted audio, and video artefacts. Proactive recapping restores the 800XL’s original performance and protects irreplaceable custom chips from voltage spikes and ripple.
Visual Inspection & Failure Signs
[edit | edit source]Before starting, examine all electrolytic capacitors for:
- Bulging or domed tops – Indicates internal pressure and imminent failure.
- Leaking electrolyte – Brown or green crust at the base or leads.
- Corrosion or PCB staining – Green or blackened areas around capacitor pads.
- Unusual odours – A fishy or acrid smell is a classic sign of leaking electrolyte.
If any capacitor shows these symptoms, replace all electrolytics on the board. Use an ESR meter if available to check for high equivalent series resistance.
Atari 800XL Capacitor List
[edit | edit source]The 800XL contains both through-hole and (in later revisions) a few SMD electrolytic capacitors. Values may vary slightly between PCB revisions (e.g., CO61563, CO61585), but the following list covers all common variants. Always verify against your board’s silkscreen.
| Ref. Designator | Capacitance | Voltage | Purpose / Rail | Notes |
|---|---|---|---|---|
| C56 | 470 µF | 16 V | Main +5 V input filter | Largest can; near power jack |
| C58 | 220 µF | 16 V | +12 V regulator input | Near 7812 regulator (if fitted) |
| C59 | 100 µF | 16 V | +12 V output filter | For SIO and audio circuits |
| C60 | 10 µF | 25 V | Audio coupling | Near audio output |
| C61 | 1 µF | 50 V | Video chroma coupling | Small axial or radial |
| C62 | 10 µF | 16 V | Reset circuit | Near CPU |
| C63 | 10 µF | 16 V | SIO input filter | By SIO connector |
| C65 | 1 µF | 50 V | Video luminance coupling | Small can, near modulator |
| C66 | 10 µF | 16 V | +5 V local decoupling | By DRAM array |
| C67 | 10 µF | 16 V | +5 V local decoupling | By ANTIC/GTIA |
| C68 | 10 µF | 16 V | +5 V local decoupling | By POKEY |
| C69 | 10 µF | 16 V | +5 V local decoupling | By MMU/FREDDIE (if fitted) |
| C70 | 10 µF | 16 V | +5 V local decoupling | By BASIC ROM |
| C71 | 10 µF | 16 V | +5 V local decoupling | By OS ROM |
| C72 | 10 µF | 16 V | +5 V local decoupling | By keyboard connector |
| C73 | 10 µF | 16 V | +5 V local decoupling | By expansion port |
Some late 800XLs (especially Hong Kong and Taiwan builds) use SMD electrolytics for C61 and C65. Replace with modern SMD tantalum or solid-polymer types if desired.
Capacitor Replacement Procedure
[edit | edit source]- Disassemble – Remove the five case screws (three rear, two front), gently lift the top cover, and unplug the keyboard and mylar flex cable.
- Remove RF shield – Desolder or carefully unclip the metal shield. Note that some shields are soldered at multiple points.
- Label all connectors – Photograph or label SIO, power, and video leads for correct reassembly.
- Desolder capacitors – Use solder wick or a spring pump. Atari used robust, high-melting-point solder; set iron to at least 350–375 °C.
- Install replacements – Match polarity (long lead = +), and use correct lead spacing (2.5 mm or 5 mm depending on position). Keep new capacitors under 13 mm tall to clear the shield.
- Clean up – Remove flux residue with IPA and inspect for solder bridges.
- Reassemble and test – Refit the shield and keyboard, then power up.
Recommended Tools & Parts
[edit | edit source]- Temperature-controlled soldering iron (60–80 W, fine chisel tip)
- Solder wick and/or spring pump
- Leaded 63/37 or quality lead-free solder (avoid cheap flux-core types)
- 105 °C, low-ESR radial capacitors (Nichicon PW/PS, Panasonic FR/FC, Rubycon ZLH)
- Isopropyl alcohol (99%) and nylon brush
- Kapton tape (to insulate tall cans touching the RF shield)
- ESR meter (optional, for pre-checks)
Post-Recap Voltage / Ripple Checks
[edit | edit source]After recapping, verify the following rails at key points (with the machine running and no cartridge inserted):
| Test Point | Expected Voltage | Max Ripple (p-p) |
|---|---|---|
| +5 V (across C56) | 4.90 – 5.10 V | < 50 mV |
| +12 V (across C59) | 11.5 – 12.5 V | < 100 mV |
| SIO +5 V (pin 10) | 4.90 – 5.10 V | < 50 mV |
| Audio output (idle) | 0 V DC | < 10 mV |
If you see more than 100 mV ripple on the +5 V rail, check for poor solder joints or a failing external PSU.
Additional Tips
[edit | edit source]- Check the external PSU first! Overvoltage or high ripple from the "in-line brick" will destroy new capacitors and custom chips.
- Retain the RF shield – It helps with both RF compliance and mechanical support for the keyboard.
- Replace tantalum capacitors only if faulty – Most Atari 800XLs use tantalums for non-electrolytic values; these rarely fail, but if shorted, must be replaced with the same type.
- Clean up any leaked electrolyte thoroughly; it is corrosive and conductive.
- Label all screws and connectors during disassembly – the 800XL has several similar-length screws.
- If you have a late SMD variant, consider replacing SMD electrolytics with solid-polymer for maximum lifespan.