LE40A336J1DXXU No Power

[Easky15]

Hi all, I got this samsung 40 inch lcd and its got no power coming from the power board, I tested the 5V_STB pin and it read 0v with power cord connected, I had a look about the board and found one of the fuses had blown, I tried replacing the fuse with one the same value but it blew straight away, Would anyone know if i could repair this on a component level, I have all the equipment and am ok with a soldering iron just don't know how to go about diagnosing the exact fault, I've included a few pics that might be usefull, Can see any other visable damage on the board apart from the fuse,

[multimeter]

Re: LE40A336J1DXXU No Power

1st thing you want to do is an in circuit test of the bridge rectifier marked BD801S ON THE PCB BOARD.

you will see on the bridge markings of -~~+


you want to test - to ~ you should have reading ONE way only,when reversing meter probes, with dmm set to 200ohm ,and power OFF AND UNPLUGGED FROM THE WALL OUTLET.


~ to ~ you should have no reading either way

~ to + should show reading one way

do these readings and report back what you find

[multimeter]

Re: LE40A336J1DXXU No Power

and the part number of ICM802....

[Easky15]

Re: LE40A336J1DXXU No Power

Ok so with the bridge rectifier still soldered in the board and powered off i tested with multi meter set to 200 ohms and didn't get any readings, then switched to 2k ohms and got a reading of .569 one way from ~ to - and a reading one way of .572 from ~ to +
Might be worth mentioning though that my multi meter is a cheap crappy one from china but its done the job for me just fine for thepast 6 months or more, ;-)

[multimeter]

Re: LE40A336J1DXXU No Power

Ok so with the bridge rectifier still soldered in the board and powered off i tested with multi meter set to 200 ohms and didn't get any readings, then switched to 2k ohms and got a reading of .569 one way from ~ to - and a reading one way of .572 from ~ to +
Might be worth mentioning though that my multi meter is a cheap crappy one from china but its done the job for me just fine for thepast 6 months or more, ;-)

bridge fine,your meter will be fine,a certain person would totally disagree

what that part number of the ic ?

[Easky15]

Re: LE40A336J1DXXU No Power

bridge fine,your meter will be fine,a certain person would totally disagree

what that part number of the ic ?

What part number of the ic mate?? Sorry not sure what ya mean.. ;-)

[multimeter]

Re: LE40A336J1DXXU No Power

What part number of the ic mate?? Sorry not sure what ya mean.. ;-)

ICM802 the 8 leg chip,thinks its the power ic

[tom66]

Re: LE40A336J1DXXU No Power

Schematic for reference:
http://www.tgohome.com/ServiceManual...&Search=Submit

[multimeter]

Re: LE40A336J1DXXU No Power

nice one tom.


check pins 7 and 8, 200 ohm setting this is VCC and GROUND what reading do you get? datasheet here

[Easky15]

Re: LE40A336J1DXXU No Power

Again I got 0 readings when multimeter was set to 200 ohms so changed it to 2000 again and now i got .699 one way only, Hope this helps. ;-)

[multimeter]

Re: LE40A336J1DXXU No Power

Again I got 0 readings when multimeter was set to 200 ohms so changed it to 2000 again and now i got .699 one way only, Hope this helps. ;-)

hmm ,strange your not getting a reading on 200ohm range twice,have you checked the battery in your meter,and for a blown fuse in the meter?.

what reading do you get when shorting the probes together?on 200ohm range?

[tom66]

Re: LE40A336J1DXXU No Power

note: on many meters 2000 ohm and diode test are the same.

[Easky15]

Re: LE40A336J1DXXU No Power

hmm ,strange your not getting a reading on 200ohm range twice,have you checked the battery in your meter,and for a blown fuse in the meter?.

what reading do you get when shorting the probes together?on 200ohm range?

Ok so i have 2 of the exact same multi meters, when both are set to 200 ohms and i short probes i get i reading of 01.2 and on the other a reading of 00.6, Maybe you could suggest a good multi meter i should invest in, ;-)

[Easky15]

Re: LE40A336J1DXXU No Power

note: on many meters 2000 ohm and diode test are the same.

Yeah thats the way these ones are, diode symbol on the 2000 ohm setting

[multimeter]

Re: LE40A336J1DXXU No Power

Ok so i have 2 of the exact same multi meters, when both are set to 200 ohms and i short probes i get i reading of 01.2 and on the other a reading of 00.6, Maybe you could suggest a good multi meter i should invest in, ;-)

the meter showing the lowest resistance (00.6)ohm is ok.

the fuse is obviously blowing due to a short,id suggest taking an ohm reading across the fuse clips and record that reading,you have a couple of heatsinks around that fuse and what looks like the stb transformer.

try removing the transistors/diodes one at a time on those heatsinks and recheck resistance across fuse holder ,if you find it goes really high resistance after removing one ,its quite likley thats the culprit.

then test the transisitors/diodes on those sinks for shorts,better results when they are removed also as you wont be picking up random resistance from anywhere else.the atlas dca tester is absolutley brilliant for doing this,it cuts the guesswork out.

[budm]

Re: LE40A336J1DXXU No Power

What resistance do you get measuring at the two legs of the main filter (450vdc CAPS laying side way)?
BTW, there are 2 fuses, one is the main AC fuse, the second is the fuse for the B+ PFC out put, so which one is blown?

[Easky15]

Re: LE40A336J1DXXU No Power

Sorry only gettin back to ya now mate, I cant get a reading due to this crappy meter, I've bought an atlas dca55 and a fluke 87 so waiting on those to arrive to do further test, But i have also found a second board the same model in my scrap board pile with what appears to be a different fault, Is there any parts i could swap from either board to repair one of them, I don't know where to start.. :-o

[tom66]

Re: LE40A336J1DXXU No Power

If you mean the top board, if that's the only fault, clean off the carbonisation and replace the blue cap.

[Easky15]

Re: LE40A336J1DXXU No Power

If you mean the top board, if that's the only fault, clean off the carbonisation and replace the blue cap.

Tried this and its now just stuck in standby,

Bought the dca atlas55, The fluke 87 is 100 quid used and the price new is a bit much, What would be a good multi meter to buy for around 100 new? So many to choose from so wanna make sure i get one that'll do everything i need,

[fbooktablet]

Re: LE40A336J1DXXU No Power

Hi,

If you really want to repair your TV and willing to shell out 100 quids i would suggest you to once visit jestine yongs site.. just google this name.
Visit his site/blog to look into some really nice repair articles with step by step photos..
If possible purchase his books which are not so expensive..
No need to buy any fancy mulimeters or such expensive equipments.
I m sure you wont regret it..

I m in no way doing any promotions here..
I m a regular visitor of his site & learnt a lot about smps repair..