Thank you for your response. I've given the chassis a good clean - with airduster, brush and "vac" - so I'm happy it isn't dirty. You're right, a defective part is not affecting the picture. However, the smell of burning "pcb" is off-putting - and there are clear scorch marks on the board around the resistor R23

TV picture looks fine but ... the smell of cooking led me to look inside. Noted R23 on main board is clearly burned and board around it is stained brown. D8 and D9 are in the same stained area. I can replace R23 but would like advice, please, on the most likely cause of the defect and therefore other relevant components which you recommend should be