Recap guide

Recap the Commodore SX-64

In the SX-64, weak or cracked caps in the 12V supply section and around the CRT circuits are linked to a dim picture and a sagging 12V rail.

Open the interactive checklist Tick off each capacitor as you replace it. It saves in your browser.

Worth a recap. Reports say it is a common and useful fix on this machine.

Which board do I have?

Boards changed during production. These notes come from the linked sources, and many are only partly documented, so check the board in front of you.

• SX-64 board assy 250408-01 (Low confidence). How to tell: Assy number from C64 Wiki. Capacitors: A repair article found the 12V rail drooping under load; no cap values. Capacitor list differs from other revisions: not known. Source

Where to start

Clues from write-ups and forum threads, not a diagnosis. Low confidence means one thread or one repair; high means several write-ups agree.

• Sagging 12V rail (Low confidence). One keyboard restoration exposed a 12V rail sagging under load and a cracked filter cap, which was replaced. Source

Tips, tales and maybes

Found in write-ups and forum threads. These are other people's reports, not tested by us. Check part references and values against your own board.

• Story: Blank screen was a stuck data line from the BASIC ROM (Low confidence). An SX-64 with a blank screen was blamed on RAM by a test cartridge, but the real fault was the BASIC ROM 901226-01 holding a data line. The author warns a dead-test flash code only shows a bus fault, not which chip causes it. Source
• Story: Rolling screen cured by a VIC-II swap (Low confidence). An SX-64 with a rolling internal CRT and black external video was fixed by replacing a bad VIC-II after a PLA swap failed. The author notes some early ceramic VIC-IIs have a raised centre that stops a heatsink seating on the SX-64. Source

Before you start

• Boards changed during production. Check your board number against the guides before you order parts.
• A tube and its high-voltage circuit can hold a lethal charge. Do not open the tube, and leave the analog board to a professional.

Manuals and technical documents

Service manuals, schematics and datasheets for this machine, kept in our own library. Check your own board and part numbers against them.

• SX 64 Portable Computer Schematics, December, 1985, 314001-05 (Schematic)

All 1 documents for Commodore SX-64 in the library

Guides we used

This page and the interactive bench are built from these. They have the photos and the full detail, so please read them and support their authors.

• SX-64 Keyboard Restoration Exposes a Weak PSU (Video) by The Retro Collective (YouTube), listed on The Oasis BBS. Shows the 12V rail sagging under load and a cracked filter cap replaced

SX-64 CPU board 250408-01

Eleven matching 10 uF 25 V parts.

SX-64 disk control board 250410-01

Console5 notes the schematic and the real boards disagree at C31.

SX-64 I/O board 250409-01

Two matching parts.

SX-64 power supply 250623

Contains a 200 V primary capacitor (C7). Unplug the machine and let it discharge before you open it, and if you are not trained on mains power, leave this one to a professional.

SX-64 monitor DEF and power regulator board 1123 / 1124 A-1

Console5 flags the 4.7 uF 160 V parts for the CJ26235-00A yoke as possibly poly, so do not replace them if so. C528 and C601 are empty. The monitor holds high voltage, so discharge it with care.

SX-64 monitor A/V board 1123 / 1124 A-2

Console5 lists two possible values at C201 and C206. The first is for the CJ26235-00A yoke and the schematic value, the other is what else it found.

SX-64 monitor chroma board 1123 A-3

Four capacitors.

Shopping list

77 capacitors in all, grouped by value. Buy a few spares.

• 18 x 10 µF, 25 V (check your board): Amazon · eBay
• 5 x 1 µF, 50 V (check your board): Amazon · eBay
• 5 x 100 µF, 16 V (check your board): Amazon · eBay
• 4 x 4.7 µF, 50 V (check your board): Amazon · eBay
• 4 x 10 µF, 50 V (check your board): Amazon · eBay
• 3 x 0.47 µF, 50 V (check your board): Amazon · eBay
• 3 x 4.7 µF, 25 V (check your board): Amazon · eBay
• 3 x 4.7 µF, 160 V (check your board): Amazon · eBay
• 3 x 10 µF, 16 V (check your board): Amazon · eBay
• 3 x 470 µF, 16 V (check your board): Amazon · eBay
• 3 x 1000 µF, 25 V (check your board): Amazon · eBay
• 3 x 2200 µF, 16 V (check your board): Amazon · eBay
• 2 x 3.3 µF, 50 V (check your board): Amazon · eBay
• 2 x 470 µF, 35 V (check your board): Amazon · eBay
• 2 x 1000 µF, 10 V (check your board): Amazon · eBay
• 1 x 0.22 µF, 10 V (check your board): Amazon · eBay
• 1 x 1 µF, 16 V (check your board): Amazon · eBay
• 1 x 3.3 µF, 16 V (check your board): Amazon · eBay
• 1 x 3.3 µF, 25 V (check your board): Amazon · eBay
• 1 x 33 µF, 16 V (check your board): Amazon · eBay
• 1 x 47 µF, 16 V (check your board): Amazon · eBay
• 1 x 47 µF, 25 V (check your board): Amazon · eBay
• 1 x 47 µF, 6.3 V (check your board): Amazon · eBay
• 1 x 100 µF, 50 V (check your board): Amazon · eBay
• 1 x 100 µF, 35 V (check your board): Amazon · eBay
• 1 x 220 µF, 16 V (check your board): Amazon · eBay
• 1 x 470 µF, 200 V (check your board): Amazon · eBay
• 1 x 3300 µF, 16 V (check your board): Amazon · eBay
• 1 x 4700 µF, 25 V (check your board): Amazon · eBay

Console5 capacitor kits for this machine

Console5 sells ready-made capacitor kits. Kits come in different versions, so match the board number in the kit name to yours and check the listing before you buy.

• Commodore SX64 Computer Cap Kit
• Commodore SX64 Monitor Cap Kit

Skip the sourcing

• Ready-made kit: Amazon · eBay
• Already recapped: Amazon · eBay

While you are in there

• Need the machine itself?: Amazon · eBay
• A box of spare capacitors: Amazon · eBay

Affiliate links. As an Amazon Associate I earn from qualifying purchases. These links only search by name. Disclosure

Step by step

1. Photograph both sides of the board before you touch anything. Zoom in on every capacitor. The photo is your map when you are three hours in.
2. Unplug it, take out the batteries and let it sit. Old power supplies and CRT parts can hold a charge. If your machine has a tube, leave the tube and its board to a professional.
3. Open it up and keep the screws sorted. A muffin tin or an egg carton works. Different screws go in different holes, and the holes never forgive you.
4. Look for leaks. Clean any sticky residue off with isopropyl alcohol and a soft brush. A leaked capacitor leaves brown crust and can eat copper traces. Look at the traces under it, not only the part itself.
5. Mark the polarity of every capacitor on the photo before it comes off. On an electrolytic, the stripe marks the negative leg. The board usually shows a half-shaded circle or a bar for the same spot.
6. Remove the old capacitors one at a time. Surface mount: add fresh solder to both ends and rock the part off, or use flux and a low-melt alloy. Through-hole: heat one leg at a time and clear the hole with wick or a pump.
7. Clean the pads and check for lifted pads or damaged traces. Clean flux off with isopropyl. A bad pad needs a jumper wire, not hope.
8. Fit and solder the new capacitor, matching polarity. Same capacity, same or higher voltage, and it has to physically fit. Work from the smallest parts up.
9. Clean the flux off and look at every joint. A good joint is shiny and shaped like a tiny volcano. A dull blob or a ball is a cold joint: reflow it.
10. With a multimeter, check for shorts across the power rails before you power it on. Use the continuity or resistance setting. A reading near zero means stop and look for a solder bridge.
11. Power it up and test everything: video, sound, controls, the lot. If something is wrong, check polarity first. It is the most common mistake and the easiest fix.

Tools

• Temperature-controlled soldering station. Steady heat so you do not cook pads. Most recaps are done between 320 and 350 C. Top: Hakko FX-951 · Mid: Hakko FX-888D · Budget: Pinecil
• Good solder. Rosin-core 63/37 flows and looks right. It is cheap and it matters. Kester 44 63/37
• Flux. Flux is what makes old joints let go and new joints flow. MG Chemicals flux pen · Chip Quik flux syringe
• Low-melt alloy (for surface mount). Melts old solder on both ends of a surface mount part at once, so it lifts off cleanly. Chip Quik SMD1
• Desoldering tool. Clears the old solder out of through-hole pads. Top: Hakko FR-301 · Mid: Engineer SS-02 pump · Budget: Solder wick
• Fine tweezers. For holding small surface mount parts exactly where you want them. ESD-safe tweezers
• Board holder. A third hand for the board, so both of yours are free. PanaVise circuit board holder
• Magnification. You cannot fix what you cannot see. Surface mount parts are tiny. Top: Stereo microscope · Mid: Head visor · Budget: Lighted magnifier
• Multimeter. Continuity, shorts and rail voltages. The one test that saves boards. Top: Fluke 117 · Mid: Fluke 101 · Budget: AstroAI
• ESR and capacitor tester. Checks old capacitors and your new ones before they go in. Top: Peak Atlas ESR70 · Budget: LCR-T7
• Isopropyl alcohol (99%) and a brush. For cleaning leaked goo and flux. Use the high-percentage kind. MG Chemicals 99.9% isopropyl
• Brass tip cleaner. A clean tip transfers heat. A dirty one does not. Hakko 599B
• Fume extractor. Pulls the smoke away from your face. Hakko FA-400 · Budget: Small bench fan
• Precision screwdrivers. Most old gear uses a mix of Phillips, Torx and security bits. iFixit Pro Tech Toolkit
• Kapton tape. Heat-proof tape to protect parts that sit close to the one you are changing. Kapton tape

Safety

• Good airflow, or a fume fan. Solder smoke is not for breathing.
• Safety glasses on. Solder spits and clipped legs fly.
• Iron in its stand when you are not holding it. Know where the cord is.
• Touch bare metal first, or use a wrist strap. Static kills old chips.
• No tube, no mains power supply. Leave those to a professional.
• Wash your hands after, especially if you used leaded solder.

Values are shown as published in the guides above, and boards changed during production. Check the board in front of you. A recap involves hot tools and, on some machines, dangerous voltages. You do it at your own risk.

More

• All recap guides
• The interactive Recap Bench
• Fix a dead vintage computer
• Commodore SX-64 on the timeline