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Repair guide

Diagnose a blank screen on an 8-bit home computer

A blank screen is often the power supply, the cable or a loose chip rather than the whole board. Work from outside to inside and keep notes.

Open the interactive checklist Tick off each step as you go. It saves in your browser.

Diagnosis · Medium · about 60 minutes. Worth doing. Reports say this fix helps on many machines.

You are in the right place if: The computer powers on but shows no picture, a black screen or garbage.

Before you start

  • Never open a mains power supply. Test only the low-voltage output.
  • Unplug before touching the board.

Board revisions and models

Machines differ in video output and PSU type.

Parts you may need

  • Known-good power supply. Rule out PSU Amazon · eBay
  • Composite or RF cable. Rule out cable Amazon · eBay

Tools

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Step by step

  1. Check the display and cable Try a different TV or monitor and cable.
  2. Check the output connection Try both the RF and composite outputs if the machine has both.
  3. Check the power supply Test the supply with a multimeter on the low-voltage side only.
  4. Look for power lights Check the power LED and any signs of life.
  5. Open and inspect Look for burnt or bulged parts, and for leaked batteries.
  6. Reseat chips Reseat socketed chips.
  7. Try a diagnostic cartridge or test Use a known-good diagnostic cartridge or program if the machine supports it.
  8. Check for a stuck key or port Unplug everything from the ports and try again.
  9. Look for guides for your model Use a model-specific guide.

Tips, tales and maybes

Found in write-ups and forum threads. These are other people's reports, not tested by us.

  • Story (Medium confidence). A Commodore SX-64 keyboard restoration exposed a sagging 12V rail, so check the supply early. Source

Guides we used

We wrote the steps in our own words from these. They have the photos and the full detail, so please read them and support their authors.

Boards and models vary, so check what is in front of you. A repair can involve hot tools, chemicals and, on some machines, dangerous voltages. You do it at your own risk.

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