BBC1 Fault 1986

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@Tomsonic41 3 жыл бұрын

Back then they used to switch the chroma signal off at the transmitter when running a B/W film, to avoid possible interference patterns on the picture. You can see them turn it back on when the fault caption comes up!

@mubd1234 3 жыл бұрын

Curious. I know they'd probably switched off the chroma signal for the film, but I don't understand why there are weird colour artifacts across the screen as the machine starts eating the tape if there's no chroma signal being transmitted.

@Tomsonic41 3 жыл бұрын

@@mubd1234 the home vcr recording the broadcast most likely got confused by the sync signal messing up. Home machines always record a colour signal even when the input is monochrome.

@mbvideoselection Жыл бұрын

No they didn't. There were strict standards that a PAL signal had to conform to and they wouldn't have the signal go off-spec so casually. They knew it could upset many different receivers, either TV sets themselves or VCRs. Cross-hatch interference patterns that arise from fine detail in a black-and-white picture when shown on a colour set were a symptom of the colour set, not of the transmitted signal, so even if they had filtered off the colour burst, it wouldn't have helped at the receiver end and, as I say, would most likely lead to erratic artefacts on-screen. If colour burst WAS lost and re-instated during this transmission, it is most likely that it was an error, and that was what caused the fault. Telecine machines in those days sent out RGB signals (Red, Green, Blue) not coded PAL signals, and were coded into PAL in Network Control. It is most likely that the picture being seen on the preview and TX monitors in the transmission suite actually looked perfectly fine, but a problem with the signal was causing a gain overrun at the transmitter site and it was this that was being seen on an off-air monitor in transmission (there always used to be at least one monitor showing an actual off-air signal so it could be verified that what was being put out of the desk was actually making it to air). They would have still had to try and diagnose any potential problems downstream from the telecine suit to Network Control making sure luma, chroma, sync and levels were all present and correct before going back to the film, even if the artefacts were being caused externally due to an out-of-spec signal being routed through the desk.