You access the signal test screen on a sky box via the services, signal test option.
This is a test screen and shows the signal strength and signal quality of a particular satellite signal.
In most cases the satellite frequency that this test screen measures is frequency 11778 v 27.5 2/3.
This is a weak satellite frequency in Spain. It is a weak Astra 2 north beam frequency. This frequency is weakest at 5pm. In many areas of Spain in the afternoon this frequency can be unavailable, even on the big 2.4m Portuguese Famaval satellite dishes.
So it is entirely possible for this signal test screen on a Sky box to show "not locked" or no signal at all, yet you are still able to receive other frequencies (and channels).
The loss of these satellite frequencies can be reduced with an accurately aligned satellite dish.
For more information please visit:
The Sat and PC Guy - Digital Satellite and Terrestrial Installations and Maintenance for the Costa Blanca
or the forum
The Sat and PC Guy FORUM - Digital Satellite and Terrestrial Installations and Maintenance for the Costa Blanca