HP21 - What's the best way to clean it?

[isanchez]

Hi,
from my expereince:

- For the keyboard (taken apart from the rest of the calculator, obviously): water & soap +hairdryer. Do not rub with anything aggressive. Use a soft cloth.
- For the circuits (not the display): circuit cleaner (spray)+toothbrush.
- For the plastic back cover: wáter & soap+ hairdryer. You can rub with something "aggressive", like a scourer... If you want to whiten the part, there are several methods on the Internet. I have tried to immerse it, for hours, in oxygenated water and oxy, under the sunlight ...and worked fine.

Regards

Ignacio