LG 50 flashing screen-no picture/sound

[Cornboats]

I have an LG 50 that has no picture or sound as such. The sceen is black but has flashing white light. Sounds rather like a fluorecscent tube when the starter does't work, Noise is coming from the left side of the Ysus board.

I 've checked voltages around the boards and pinouts correspond with written values etched on boards .

I've swapped the y-sus and z sus boards with ones that I thought were ok & sympton remains the same.



What to check next?