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Recap guide

Recap the Sinclair ZX Spectrum

A widely recommended preventive recap, with cheap kits and capacitor lists by board issue for the 48K.

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.

  • 48K Issue 1 (Medium confidence). How to tell: Light fawn keys per older spec sites; no capacitor designators on the silkscreen. Capacitors: Has a good number of radial caps plus axials; some radials are unmarked. Heat sensitive ones near the heatsink suit 105C parts. Capacitor list differs from other revisions: not known. Source
  • 48K Issue 2 (Medium confidence). How to tell: Blue keys; all memory on the main board. Capacitors: Lists C25, C27, C28, C34, C44, C45, C46, C47, C50, C65, C74; C46 is fitted opposite its silkscreen, C65 is 22uF or 100uF, C74 is radial. Service manual says a few early units used disc caps for 47uF and 100uF. Capacitor list differs from other revisions: yes. Source
  • 48K Issue 3 and 3B (Medium confidence). How to tell: Dark keys with heatsink visible in the edge slot; heatsink moved to the back. Capacitors: Issue 3 set is Issue 2 plus C78 and C79 as service mod parts, C47 optionally deleted; 3B is the same. Capacitor list differs from other revisions: yes. Source
  • 48K Issue 4A (Medium confidence). How to tell: First widely seen in the Spectrum+ case; regulator at the back near the edge connector. Capacitors: 11 caps: Issue 3 set without C78 and C79, C47 restored. Capacitor list differs from other revisions: yes. Source
  • 48K Issue 4B (Medium confidence). How to tell: Same regulator position as Issue 3; virtually identical to 3B on the ntnu summary. Capacitors: 12 caps: C47 removed, C79 and C80 added. Capacitor list differs from other revisions: yes. Source
  • 48K Issue 4S (Medium confidence). How to tell: Samsung made, green solder mask both sides, S01 serial prefix. Capacitors: 12 caps, like 4A plus C78. Capacitor list differs from other revisions: yes. Source
  • 48K Issue 6A (Medium confidence). How to tell: Final 48K issue with provision for a reset switch on the PCB. Capacitors: 12 caps matching the 4B set. Capacitor list differs from other revisions: yes. Source
  • 128K, grey +2 and +2A/+3 (Low confidence). How to tell: 128K versions 2, 6K, 6U; grey +2 Z70500 (Taiwan) or Z70700 (UK, axial caps); +2A/+3 Z70830, Z70833, Z70835 with one gate array. Capacitors: No cap list found; the +2A/+3 drops the DC-DC converter and uses a 6 pin DIN supply. 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.

  • Lists by issue (High confidence). A list for the 48K range covers Issues 1 to 6A, and a retailer sells per-issue kits that include ceramics. Source
  • Why electrolytics dry out (Medium confidence). One guide explains why electrolytics dry out and gives a kit list for the 48K. Source
  • +12V ripple (Low confidence). One forum post points at C44, C45 and C74 on an Issue 2 board for ripple on the +12V rail. 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.

  • Tip: Replace the diodes with the cap in the PSU (Medium confidence). In an issue two repair thread, a poster found 50Hz ripple pointing to a faulty rectifier diode in the 12V path and advised replacing all four diodes as a set, plus any tired electrolytic, or just using a modern 9V supply. He calls the 7805 fairly reliable. Source
  • Watch out: Too much input voltage hurts the DC-DC converter (Medium confidence). On a Spectrum that kept resetting, a poster warned early machines expect about 9V and an overvoltage supply can kill the DC-DC converter; the owner's supply read 13.4V. He saw 600mV spikes on the Z80 supply and planned to recheck the electrolytics he had not yet replaced. Source
  • Tip: Priority caps and the -5V trap (Medium confidence). A forum regular says all Sinclair machines are old enough that the critical electrolytics should be replaced, especially those near the 7805 heatsink. The thread notes losing +12V upsets the DRAM and a lost -5V can destroy memory chips on the DC-DC converter boards. Source

Before you start

  • Boards changed during production. Check your board number against the guides before you order parts.

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.

The capacitor list

We have not checked a capacitor list for this machine yet, so none is shown. Follow the guide above for your board, then add the capacitors in the interactive checklist and it builds a shopping list for you.

Skip the sourcing

While you are in there

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Steps, tools and safety

The steps, the tools in top, middle and budget picks, and the safety list are the same for every machine, so they live on one page: How to recap, step by step.

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.

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