Ok, get ready to give your FARFISA COMPACT some serious spring cleaning (it's a joke, you're not supposed to clean any springs).
First, open up the baby. Unscrew anything that holds the big keyboard in place. You might also have to loosen some screws that fix some cables. If you're finished, you should be able to pull the keyboard out of the wooden corset.
In the picture: Two of your best cleaning buddies: Isopropyl alcohol (ONLY use the 99% brand NOT less, because it will eventually worsen things!) and pipe cleaners (use expensive ones because the cheapos will lose a lot of tiny hairs for which your Farfisa internals have no use for).
Lose any screw and cable (e.g. the white cord connected to the reverb unit) so you can pull the keyboard out and move it up vertically (lean it onto a wall, that's best, but be careful not to break anything, like the oscillator cards). Make it look like this:
Good work so far! Now you can access a lot of the key contacts. They are the tiny wires that are connected with the keys and mysteriously disappear into tiny holes. Use pipe cleaners to give them a healthy rub and get the dirty stuff off of them. Also, a toothbrush might come in handy.
As you can see, the interior of my Compact is pretty dusty. Spiderwebs, dirt, sawdust, fingernails, confetti... I even found some Pot in a Compact Duo once! Scrub away as far as you can get. The pipe cleaners make it possible to get into those tiny holes as well. Drench them in alcohol first.