Vestel SMPS 17PW26-3 run from self from Stand By in work regime

[GP ELECTRO]

I have one Vestel LCD on repair, problem is with SMPS 17PW26-3 Board.
LCD works fine till you put in Stand By. After e few minutes (1-2 minutes) the set run from self in work regime and picture and sound are OK.

I have replaced the power board(17PW26-3) with new one and the TV set works fine again.
I want to try to repair this defect board but have no idea where can be the defect.
I have changed the opto IC811, Q805,Q804,Q845 but without result
I have found that on board which is good the STB is 3.3V and on this defect board this STB is 3.4V. Is this 0.1V very important or no ? It is not important, I have change the STB voltage to 3.2V.  With STB 3.2V works and the power board switch on from self

Does anybody has any idea where can be the defect 
Many thanks in advance for any good idea and help
Regards
Peter

[jordan]

Moor problems on this power board make this two capacitors C877 and C878 (12nF/630V)-change !

[GP ELECTRO]

Thanks Mr.Jordan for your reply,
but in my SMPS there is only C878 and it's OK because my power board works fine till is in Standby position.
When the unit is in Standby after a minute the board run from self in working  regime (picture and sound appear).
I have finished the TV set with new power board, but I try only to repair the defect board
Have a nice day
Peter

[GP ELECTRO]

The problem was fixed after replacement of resistor R817, R818 and R819 ( all are 300K )