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

[rolfmwa]

Hello all,
Hooray - I've managed to buy a functioning HP21 which looks a little grubby.
Can I use alcohol to clean it ( I really don't want to damage it any further)?

Also, what is the best way to replace those 4 (grubby?) pads the calculator rests on?

Any advice greatly appreciated!

Rolf

PS: Once cleaned I will post some pictures

[PANAMATIK]

Congratulations for your HP-21!

This calculator is safe to be cleaned with alcohol or isopropylalcohol, because it has no labels printed on the keyboard plane. Also the buttons are double injection molded and hence resistant to cleaning. The yellow labels of HP-22/25/27/29 however may not be cleaned with alcohol, they can be washed away.

Don't use acetone for cleaning the housing, it would dissolve the surface.

The rubber feet can be replaced by white eraser rubber.

Bernhard

[Kees Bouw]

Hi,

I would be extremely careful with using alcohol on the keyboard even if there are no labels printed on it. The alcohol can damage the clear matte finish and cause a shiny surface. I have learned this the hard way when I used alcohol to clean the keyboard of a HP-67, just on the black areas, and I removed the matte finish. I have tried several types of paint to restore it but without success.

Kees.

[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