Recap guide

Recap the Sinclair QL

Owners generally report the QL's own board capacitors lasting well, so the usual trouble is elsewhere: the keyboard membrane, microdrives, the plug-in power supply and the hard-working 7805 regulator. The exception reported is US-market boards, where one supply capacitor near the right microdrive connector has failed.

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

Check first. A recap is not always the answer here, so look at the guides before you order parts.

Where to start

We did not find a clear list of what fails first on this machine, so we are not guessing. Read the guides below, check the board for leaks, and replace what you can see.

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.

• Tip: US boards: C42 and neighbours (Medium confidence). One experienced repairer reports two failed supply capacitors on US QLs, both C42 above the right microdrive connector. As a precaution he replaces the seven capacitors in that area plus C4 (between the ROM port and the 8302). Others in the thread say UK boards have given far less trouble. Source
• Tip: Membrane first, caps rarely (Medium confidence). A veteran says he has never had a failed capacitor in a QL (the design leans on tantalum and ceramic decoupling) but that an original keyboard membrane is very likely dead. His pre-use checklist: 7805 firmly on its heatsink, PSU electrolytic tops flat and dry, no bent expansion pins, chips seated. Source
• Tip: Regulator at its limit (Low confidence). A museum-style write-up of a restored QL notes the 7805 runs at its load limit and needs a big heatsink or a DC/DC converter. The same page records a brittle original membrane, a worn left microdrive bearing and a replaced mains plug. Source
• Watch out: Test a PSU under load (Low confidence). In a thread about a homemade supply, posters note the 7805 needs roughly 7V at its input to make 5V, and that a supply reading fine unloaded can sag under load. Advice was to load-test with a bulb rather than risk the QL. Source
• Story: Lost 15V AC was a transformer winding (Low confidence). One QL supply lost its 15V AC output while the 9V DC side still worked. The owner traced it to a degraded transformer secondary rather than a failed part. A reminder that the original wall-wart style supplies age too. Source
• Story: Buzzing PSU, half-synced display (Low confidence). A QL owner with a buzzing supply on one machine and a display that would not sync on the bottom half on another was told the 9V DC side was probably collapsing under load. They gave up on the originals and bought a modern replacement supply. 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.

• Which capacitors to replace? (Forum) by The QL Forum. Community thread on which capacitors matter, with the US-board C42 report.
• Useful inspections before using a QL (Forum) by The QL Forum. Visual checklist for a QL that has been in storage.
• Sinclair QL (museum page) (Blog) by shred museum. Restoration notes covering membrane, microdrive, PSU regulator and connector.

Main board (14 parts)

From oldcrap.org's list, noted from the original parts. Seven are axial parts (a lead out of each end). One owner report says C42 is the one that has failed on US-market boards.

Shopping list

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

• 6 x 22 µF, 16 V (check your board): Amazon · eBay
• 3 x 4.7 µF, 16 V (check your board): Amazon · eBay
• 2 x 470 µF, 25 V (check your board): Amazon · eBay
• 1 x 0.33 µF, 50 V (check your board): Amazon · eBay
• 1 x 47 µF, 10 V (check your board): Amazon · eBay
• 1 x 100 µF, 25 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
• Sinclair QL on the timeline