HP 21 not powering on - repair/troubleshooting advice

[aurelio]

(01-27-2021 11:44 PM)dmh Wrote:  

(01-27-2021 09:41 AM)aurelio Wrote:  Don't worry: the bath is a well-established procedure, especially for this type of machines...
You can read about on many other discussions on this Forum.
First take apart the display which does not need any treatment, then drop the printed circuit board in a tray containing a glass of water and 3 tablespoons of vinegar cooking (I use the apple one). leave it for at least one day, then rinse everything under the tap and let it dry for another day, better if on a sheet of absorbent paper.

Let us know
Hope this helps
Aurelio

What about the circuit board with the keyboard and front of the calculator? Can that be bathed too?

Thanks

I would avoid dipping this part if you have not removed the keyboard first. If it shows signs of corrosion then clean it too, but with a sponge. To remove the keyboard you have to cut the plastic rivets and therefore you need extra work to restore them.... remove the keyboard only if there are false contacts and you have to clean (with a thin sheet of paper) ... if you browse the forum in another discussion it is explained how to do in detail. If I've undersood the issue (do not power up at all) and you see traces of green on the printed board simply try to do the first step (this way you also clean the battery contacts). if the calculator power on now, can go ahead, checking the rest
Have fun