panasonic 40CX400 flickering backlight after psu repair

[disorder]

hello,

this one makes me mad
got a pana 40CX400 that came with led blinking issue, no start , no backlight
after inspection , Q502 short, replace it but no more
so replace MPS3394
then when plug in all 1R00 resistor between Q502 and ground blowned, Q502 too

find that diode between MPS3394 and Q502 was defective

so replace all 1R00 resistor, Q502 and replace diode with 2R2 resistor as it is on many other 17IPS20 board

now, no blown thing !! yes !!

but backlight flickers , it start for one second then off, then on one second ....

what can cause that ? do you already seen that ?

thx

[disorder]

Re: panasonic 40CX400 flickering backlight after psu repair

hello,

some news, got one (??!!) led blown
so replace it, now the backlight is ok

but....

i can't rise the backlight, it always stays at the same intensity. can't rise or down it on menu : can go from 0 to 100 percent , but no change on the tv, and the backlight is very low.

i have checked pw_dimming and it is at 2.6V , on MP3394 schematics it says it goes from 0.6 to 1.6v, but can't understand why at 2.6 it is very low...

the resistance between pwdimming and mp3394 seems good : 1kohm

maybe a motherboard issue ?? do you know what can i check for now ?

thank you

[Biruslapio]

Re: panasonic 40CX400 flickering backlight after psu repair

Was there any input at the selected source when you adjusted the backlight? I know this is a thing for some LGs, never tested on a Panasonic, eco mode may interfere with it too.

[disorder]

Re: panasonic 40CX400 flickering backlight after psu repair

hello

yes test with input on hdmi, not any change at all.

i want to test with direct input on 3rd pin of mp3394 but i have to find a correct voltage on board first, as this i will maybe be able to see if it is a regulator issue or a pw_dimmin problem.

[dick_barton]

Re: panasonic 40CX400 flickering backlight after psu repair

What voltages do you have on Pins 15 (VCC) and Pin 16 (VCC) of the MP3394

I would not have considered replacing a diode with a resistor since they have completely different properties