Roger Lambert is at Dr. Blake's house repairing the television when Blake receives a phone call to rush to Tyneman's Electronics Store because Simon Lo has been attacked. In the very next cut, as Blake arrives at Tyneman's, Lambert is clearly visible in the background in the doorway to the store.
To test the prize TV for a fault that causes electric shock an electrician would use an Insulation Tester not a Voltmeter. Voltmeter might check for shorts or open circuits but not live touch surfaces.
No need to make phonecall to close down dressing room. It would have already been closed as a crime scene.
Television was not rolled out in Ballarat till 1961. Doctor Blake Mysteries is set in 1959.