HP-21 - Crazy numbers

[BusyCalc]

Hello,

thanks for the tips!

Is it then possible to immerse completely the main PCB in vinegar? Is it not hazardous for the chips or the coil?

How do you rinse it afterwards? With distilated water?

Apart from this, I've noticed that the back of the LED PCB was dirty with something similar to black dust, like carbon particles. I could clean it a little bit with isopropyl alcohol, but it remained quite dark. I saw also that the pins that are inserted in it have black parts, specially the parts that get in contact with the holes of the PCB.

I tried to clean the pins but in this case I saw no improvement, they are still partly black. I don't know if they are burnt or simply I'm not using an appropriate cleaner.

Good is, that the calculator works perfectly, but I'd like to clean everything properly and increase the posibilities that it works for many years. I have a bad feeling when I know that there are still some rests of corrosion and dirt inside.

Kind regards.

Oscar