Greetings.Do you mean a loud crackling type sound when you switch on or off?

It could be the sound output chips as you say,but it's unusual for both to go.

A common cause of this noise is poor grounding of the crt metal rim.Clean the gold coloured s shaped hooks that anchor the earthing band,and where they connect to on the crt.

N.B. Don't go inside a tv unless you are confident.There are dangerous voltages present even when the set is disconnected!!

Thanks for the suggestion, I will see to it.

Its hard to describe the noise, but it is not only when switching on/off, it is allways there, also if the unit is on internal speakers.

Don't worry I have repaired this tv several times.

I have cleaned the gold coloured hooks, they where quite dusty.

Seems the works at start-up, but after a while the 'craking' noise is back.

As I replaced the 'Video and sound switching boards' it must be someting on the main board.

Any sguggestins or hints are welcome.

As cleaning the crt grounding clips seems to have made a difference,could it be that the connection is poor further along?Check the crt base connector,they are notoriously troublesome.Clean the crt pins (carefully)and check the grounding is continuous through to the main chassis.

I've had this problem where it was caused by a noisy chip on the av board,but you say you replaced this board.(The one with the scart sockets)

If the noise is not there when you listen via the headphone socket,it has to be due to the speaker relay RL1.Tapping the relay will prove this.

Otherwise,it's worth checking the caps etc in the muting circuit,eg C64,D29&30,C71,70,61&62.

Regards,

nick