As per the author of this video's advice I took the parts from a non-working PC motherboard. When I finished adding the crystal the ON/C/C procedure worked as expected. I thought everything was ok, but I noticed programs would not run anymore. Also, the pixels in last row of the first line of the display almost always were shifted. I hadn't measured the value of the SMD capacitors because the digital multimeter in the picture would not measure in the pf range. I measured them later using another multimeter and they turned out to be 34 pf each. I replaced them with 10 pf ceramic caps but the problem remained (I shouldn't have used those large caps but I did it as a test). Anyway, I've managed to set the time according to the Windows clock. After two hours both clocks remained perfectly in sync. It has occurred to me the batteries are far from fresh (I've been using them for seven months now). After resetting the calculator I ran a program for five seconds. The batteries voltage dropped from 2.9 to 2.6 volts. Perhaps it's time to finally replace the batteries (and update the firmaware). I suspect the batteries drain more current when a crystal is installed. I'll replace them next Monday.
Gerson.
P.S.: The sledgehammer was not necessary :-)
Edited: 18 Feb 2012, 6:00 p.m.