panasonic TH-42PX8BA dead

[cooper1973]

can anyone shed any light on what the problem could be everytime i plug tv in and switch it on it just blows the fuse in the plug it clicks to turn on but as soon as this happens the fuse then blows. does this indicate psu board? i know psu going faulty is a common problem

[t1412]

yes it does, if you take the back off you may find the components may have  burnt out if you get the chance can you take a picture thanks 


regards
shaun
 

[cooper1973]

thanks for your reply shaun i have attached photo of psu but i can not see any obvious signs of blown components which has puzzled me as thought there may of been a blown cap. do you know what component is usually at fault?

[t1412]

check 1 of the  disc caps in the top right corner c478 i think it looks like it's spilt or it could be a hair

shaun   

[cooper1973]

hi shaun i have just checked the disc cap top right hand and does look fine but see what you mean about the pic. i have just bought a new board but wish i could fix this one and keep as a spare any idea if the is a common part that goes on these boards?

[t1412]

have you got a meter, check f402/pr401/glass type fuses and f403 wickman fuse. if ok then check diodes d419/420/429/435/439/  in both direction if ok brigde chip zn401 then transistors q406/q412/q413 and the 5 transistors on the large heatsink

[cooper1973]

im not getting any reading at all from the bridge chip zn401 i have tried in both directions as i done with diodes. i take it i should get some sort of reading. the chip is open both ways

[t1412]

if you can take it out of the circuit to get a proper test on the meter

shaun

[cooper1973]

i had taken this out and still no reading on multimeter. i also took another one out that is also on the board and no reading on that either. on of the trasistors on the large heatsink is also showing no reading on one of the legs but others are fine

[tv tony]

Please take this a bit of advice, not to be taken as an insult, but you are working with rectified mains (310v) and after pfc this can be approaching 400v. This can be a killer! A diode should conduct one way and not another, testing a bridge is similar. When you say the diodes are not conducting in either direction worries me, have you got your meter on the right range and function? Keep us posted if only to say you are not fried.
Regards,
tony walker

[watteau]

Hello,
Just a quick thought, I notice the fuses on the board are rated at 8A, what size fuse are
you using in the plug (13A)?
Regards,
John.

[cooper1973]

no im using 5amp why would you want a 13amp in the plug?????

[cooper1973]

Please take this a bit of advice, not to be taken as an insult, but you are working with rectified mains (310v) and after pfc this can be approaching 400v. This can be a killer! A diode should conduct one way and not another, testing a bridge is similar. When you say the diodes are not conducting in either direction worries me, have you got your meter on the right range and function? Keep us posted if only to say you are not fried.
Regards,
tony walker

cant see anywhere that i said diods are not conducting in any direction im puzzled????