After a couple of contacts I dug my trust keyer based on PIF16F84, opened it to insert the second AA cell required and I discovered that one battery had leaked on the circuit board covering the IC with salt.
Ouch! What I loved of this keyer was that it lasted forever on a couple of AA batteries. Unfortunately I am not able to program a 16F84 anymore, so I will have to switch to something else. Fortunately there is a fairly complete (and complex!) keyer based on Arduino/AVR boards by K3NG, so I am probably going for it.