Hello,
The problem : TV does not start at all.
TV model :THOMSON 40FA3113
PCB : MT31EPA-MAC2HG
The fault is located in the primary of the SMPS.
The shorted power MOSFET appears to be the cause of the problem. So I changed the transistor (QW1 which is a 10N65B), the bypass capacitor (C409 which was a ceramic 220pF before exploding), and the fuse.
But now I'm stuck because I spotted a defective small signal zener diode (Z402) that I can't replace because I have no way of knowing its value. There is no marking on the PCB, the package is SOD-80(miniMELF) with a blue stripe.
Here is the schematic I drew based on my PCB :
I haven't found the schematic of the PCB so I can't identify it in this way either, however I managed to find the schematic of another version of this card (MPLE31N75-2B-T, see attachment below, page 15) where this diode does not appear, this which makes me think that its role is not crucial and that the card could work without it. But before doing anything I would like your opinion on its role in the circuit. Perhaps we can guess the order of magnitude of its zener voltage?
Finally, i have tested all the diodes and transistors in this area and it's all good but i don't know if the flyback controller (RT7736B) is dead or not.
Thank you.