Recap guide

Recap the Kaypro II

Same story as the Osborne: the rice-paper RFI caps in the power supply are the ones that blow.

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.

• Kaypro II main board 81-110-A (Medium confidence). How to tell: Early board, serial 4037 in one repair log. Capacitors: Only four electrolytics: C19, C20 and C69 at 47uF 10V and C4 4.7uF 35V. Capacitor list differs from other revisions: not known. Source
• Kaypro II main board 81-110-B1 (Low confidence). How to tell: Later board, #36311 in the same log. Capacitors: Cap list not given. Capacitor list differs from other revisions: not known. Source
• Kaypro II supplies (Low confidence). How to tell: The early machine had a California DC supply, another page shows an Astec AA12450. Capacitors: No cap lists. 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.

• Blown RFI caps (Medium confidence). One repair after smoke from a Kaypro II found the RFI suppressor caps had failed (4.7 nF per the spec, plus one 0.22 uF) and shows what replaced them. Source
• Power supply electrolytics (Medium confidence). Another repair replaced four electrolytics, lists their values, and notes which ceramics were left alone. 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: RFI cap pop and smoke (Medium confidence). A Kaypro II popped and smoked when an RFI suppressor blackened. The author replaced three 4.7nF caps with spare 10nF ones after forum friends said they would do, and noted a larger 0.22uF cap would likely go next. Source
• Story: Kaypro II low +12V and four caps replaced (Medium confidence). A Kaypro II repair log replaced C19, C20 and C69 (47uF 10V) and C4 (4.7uF 35V), and found the supply gave +10.5V when at least +11.5V was needed. The output voltages were adjustable on the California DC supply. Other faults were chips and corrupt ROMs. Source
• Tip: Two supply makers: Astec and California DC (Medium confidence). A write-up says Kaypros used either an Astec supply (white PCB) or a California DC one (blue PCB) and that many Kaypros, like Apple IIs, have supply caps that pop and smoke as paper insulation fails. Identify which supply you have before ordering parts. Source
• Story: Kaypro 4 intermittent power and dimming (Low confidence). A Kaypro 4 thread with drives not getting 5V and the display dimming drew advice to start with the electrolytics, inspect high-current solder joints with magnification, and replace supply parts one at a time. One owner recommended recapping all boards. Source

Before you start

• Boards changed during production. Check your board number against the guides before you order parts.
• A mains power supply can hold a dangerous charge. If you are not trained to work on one, have a professional do it.

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.

• Smoke from a Kaypro II. The fault and the fix (Write-up) by Terry Stewart (Classic Computers NZ). Has a capacitor list. Identifies the failing RFI caps and what replaced them
• Kaypro II repair (Write-up) by Thomas Brase (retrocmp.de). Has a capacitor list. Replaced four electrolytics with values and listed the ceramics left alone
• Kaypro II (List) by oldcrap.org. Cap list exists only as an image on the page
• Tech Flashback: Reviving the Kaypro 4 (Write-up) by Gough Lui. Mentions the PSU cap issue only in passing

Power supply (17 parts)

oldcrap.org's list, noted from the original parts. C1, C2 and C13 are the film suppression caps (the RIFA type); the page also lists the four 100 uF 250 V cans as C5 to C8. The existing write-ups say the RFI caps are the ones that blow, so do those first.

Monitor board (16 parts)

From the oldcrap.org list for the Kaypro II's built-in monitor board.

Motherboard (2 parts)

From the oldcrap.org list. Only two electrolytics are listed on the motherboard.

Shopping list

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

• 5 x 2200 µF, 16 V (check your board): Amazon · eBay
• 4 x 100 µF, 250 V (check your board): Amazon · eBay
• 3 x 47 µF, 16 V (check your board): Amazon · eBay
• 3 x 1000 µF, 16 V (check your board): Amazon · eBay
• 2 x 0.01 µF, 250 V (check your board): Amazon · eBay
• 2 x 47 µF, 35 V (check your board): Amazon · eBay
• 2 x 100 µF, 25 V (check your board): Amazon · eBay
• 2 x 100 µF, 16 V (check your board): Amazon · eBay
• 2 x 220 µF, 10 V (check your board): Amazon · eBay
• 1 x 0.1 µF, 250 V (check your board): Amazon · eBay
• 1 x 1 µF, 50 V (check your board): Amazon · eBay
• 1 x 2.2 µF, 50 V (check your board): Amazon · eBay
• 1 x 4.7 µF, 50 V (check your board): Amazon · eBay
• 1 x 10 µF, 25 V (check your board): Amazon · eBay
• 1 x 10 µF, 16 V (check your board): Amazon · eBay
• 1 x 22 µF, 160 V (check your board): Amazon · eBay
• 1 x 33 µF, 16 V (check your board): Amazon · eBay
• 1 x 47 µF, 25 V (check your board): Amazon · eBay
• 1 x 47 µF, 160 V (check your board): Amazon · eBay

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
• Kaypro II on the timeline