Inside the Kosmos CP1

Originally, I planned to save all the CP1 stuff for a later post, but there’s this one picture I really want to share. After removing the cardboard back cover, this is what I saw:

Inside the CP1: a screwdriver
After removing the cardboard back cover, this is what I saw. The screwdriver must have been in there for some 15 years at least.

Bringing an old computer back to life

Returning to the retrocomputing hobby after 12 years, most of my collection has been in storage way longer than I anticipated in 2006.1 That means I’ll have to treat every machine I take out of storage essentially as an unknown. That’s why I looked around on the internet for some best-practice checklist on how to proceed with “new” old computer, but couldn’t find anything.2

So here’s my attempt. I’ll extend and modify it as I take more and more machines out of storage. I welcome your feedback.

The basic idea behind all this is that an “unknown” machine may be damaged, and that powering it up in one piece without fixing the existing damage first may make matters worse. For example:

  • The machine’s power supply may have degraded to the point where, while still seemingly working, the output voltages are way out of spec and will do damage to the components over time; worse, it may even explode.
  • Corrosion from water damage or leaked batteries may cause further damage when the device is turned on.


  • Take lots of photos. You’ll never know when knowing the original state of something might come in handy.
  • When you need to disassemble anything, make notes about position and orientation of disassembled parts; carefully note which screw goes where.
  • Don’t hurry, work step by step and be careful not to damage anything. Spare parts are hard to get.
  • Always be grounded when touching disassembled electronic parts (of course, you schould not touch anything which is connected to the power source…). Use an antistatic mat when laying down those parts. Again, spare parts are hard to get.
  • Mains voltage is dangerous. Do not open a system that is connected to the mains unless you know exactly what you are doing. Note that power supply capacitors can remain charged long after you have disconnected the system from the mains.
  • CRT monitors work with acceleration voltages of tens of kilovolts. Never open them, unless you know how to safely work with them.

Get Background Information

  • Gather what you know from the previous owner.
  • Do an internet search for the particular model in front of you. Look for
    • service manuals,
    • schematics,
    • repair/refurbishment reports, and
    • test / diagnostic software.

Inspect the Machine Carefully before You Turn it On

  • Do a basic cleaning and a visual inspection of the outside.
  • Check the operating voltage. If there are multiple voltages, see if there is a voltage selection switch, and if so, if it is in the correct position.
  • Open the case (unless, of course, this would do permanent damage to the machine; remember, this is about limiting damage).
  • Get out the worst of the dirt.
  • Remove or disconnect all expansions, add-ons, internal drives, etc.
  • Visually inspect all boards. Pay particular attention to
    • batteries (which may have leaked)
    • electrolytic capacitors (which may have leaked or bulged / crumpled)
    • solder joints on parts subject to mechanical stress, like connectors (which may have broken, creating a “cold” solder joint)
    • previous repairs or repair attempts
    • ICs that seem out of place, e.g. having a datecode that doesn’t match the rest of the system
  • Remove leaked batteries and leaked / crumpled capacitors. Clean up. Note permanent damage. Replace capacitors.
  • Resolder cold solder joints.
  • Be suspicious of any previous repair. Check that the right component is in the right place in the right orientation.
  • Note mechanical damage.
  • Measure board resistance between all rails to detect shorts.
  • Press all socketed IC down gently, but firmly.

Check the Power Supply

  • Disconnect the power supply from the rest of the machine, if possible.
  • Check all power supply voltages under load and no-load conditions. If you have an oscilloscope, look for excessive ripple, too.
  • Note that some switch mode power supplies do not like being without load. They may not turn on without a minimum load, or worse, may sustain damage.
  • Only when the power supply checks out, connect it back to the main board.

Test the Machine

  • Power up the machine.
  • Look out for diagnostic messages from the ROM / BIOS / Kernal / etc.
  • Run diagnostic software (if available), or any other kind of software that puts the machine through its paces (if not).
  • Plug in expansions and add-ons one by one (when the machine is turned off, of course). Test separately.
  • Fix issues as they arise.3

Prepare the Machine for the Future

  • Remove or replace components that are likely to fail, like batteries (even if they haven’t leaked / failed *yet*). Some people replace all electrolytic capacitors, some even replace voltage regulators. I’m still on the fence about that – it’s about balancing risks.4
  • Ensure all components that need to be heatsinked are properly heatsinked. Add thermally conductive paste (sparingly!) where necessary.
  • Clean thoroughly. This may include
    • cleaning flux residue from solder joints with isopropanol
    • disassembling, cleaning, and reassembling the keyboard
  • Retrobright, if you want to.

UPDATED September 6, 2018