TV pictures that freeze or appear ‘blocky’ are usually caused by a weak signal. This may be due to the customers address being outside of coverage, poor cable connections or certain weather conditions, especially high pressure.
Try the following steps-
Check the predicted Freeview coverage and channels available for the customer’s address using the coverage checker on the DigitalUK website: http://www.digitaluk.co.uk/coveragechecker
If the checker predicts good coverage, try retuning the TV or digital box to reload channels
Check the conditions of cabling and connections. Damaged or loose aerial plugs can cause problems. Try disconnecting aerial amplifiers or spitters which can sometimes lead to equipment getting overloaded or too little signal