Now use two pieces of wire to connect X1 to X2 and plug the mains power back in. You should now find a voltage between 15V and 18V on X2 (and X1).
I measure around 6,9V
#
If you connect pin 2 of the IC1 socket to VDD (e.g. pin 14), the voltage on X2 should drop to between 5V and 7V.
I measure 5,5V.
Measure the voltage on pin 18 of the IC1 socket with pin 3 left open and again when it is connected to ground. In the former case the voltage should be below 1.25V (it is actually expected to be 0V). In the latter case the voltage must be above 1.25V (and will probably be close to 5V).
(feedback: don't try to tell a story because it isn't, so make a step by step plan like below).
* On the IC1 socket, measure the voltage on pin 18,
and ground (pin 5)??. The voltage should be below 1.25V (it is actually expected to be 0V)
I measure 4,07V
##
* Connect pin 3 of IC1 to pin 5 (ground) and measure again the voltage between pin 18 and pin 5 of IC1. The voltage must be above 1.25V (and will probably be close to 5V).
I measure 4,46V
So measure
# and
## are incorrect, but the trouble shouting doesn't tell what to do.