LG LCD power supply

[vinceroger69]

Re: LG LCD power supply

budm before i solder the ic in on the good psu where the four legs are soldered together and where the three legs are soldered together theres a short still as in dead short on the pcb pads. i forgot i still had that one link lifted to do your test.

[vinceroger69]

Re: LG LCD power supply

u200
303735
609p
coa88

[vinceroger69]

Re: LG LCD power supply

removed both the ics on the good board now and the short between the 5v st and ground is stll there? so not sure where the short reading is coming from im sorry in above posts i still had that one link un soldered.

[budm]

Re: LG LCD power supply

I am confused now, so the original board you are working on, the short is gone when you remove one of the IC (MOSFET), right?

[vinceroger69]

Re: LG LCD power supply

sorry budm only the good board im talking about now i thought when i first removed the mosfet the short had gone but i forgot i still had one of the wire links lifted which you asked me to remove earlier when i resoldered a good mosfet in and re soldered the wire link the short came back so i removed both mosfets and the short is still there with the wire link re soldered hope this makes sence now.

[budm]

Re: LG LCD power supply

So the good board is the board we were working on in the beginning that shows shorts on the 5VST pin, then we remove the jumper on the right side then the shorts on the 5VST is gone.
Then Q204 and 205 were tested off the board and the Q204 shows short circuit between the S and D pin, but 205 is not shown as short, diode D207 is also shown OK, that is correct? So If you lift that link again, the short on 5VST is still there?

[vinceroger69]

Re: LG LCD power supply

if i lift wire link short goes on 5v st and gnd pins but at the minute i still have the two ics removed i will order two new ones to rule them out and maybe u200 as you say that area is heat damaged anyway and the parts are cheap.

so basically with the wire link installed the two mosets removed the short is still there on the 5v st and gnd pins so must be something else too shorted.

[budm]

Re: LG LCD power supply

So Would leave one end of the jumper lifted, as you can see the feeding path for the 5VST into that 3.3V circuit, you can see C202, C207 and then L201, the output side of theL210 is connected to C208, the drain pin of Q204 which that is all I can see in the picture, I cannot tell where else the output side of L201 goes to.
So what you can do is to remove L201 and see if the +5VST input I marked still show 0 Ohm or nor if not then the shorts is after L201.
We have to isolate the circuit. If the shorts is still ther then I would remove L204 and see.

[budm]

Re: LG LCD power supply

u200
303735
609p
coa88

Nothing comes up on those numbers.

[vinceroger69]

Re: LG LCD power supply

budm thanks for your help so far i will try again tomorrow and get the part number also some clearer photos its gone dark here now so struggling to do anything so i will have another look in the morning im in no rush this is a set someone got from a rubbish bin so if i cant fix it no loss i just like too gain experience etc.

[vinceroger69]

Re: LG LCD power supply

Budm ive had to put this psu on hold for today as other jobs more important but so far ive removed q204 q205 u200 off the board and will place a order for some but the short is still on the board somewhere (will wire link still in place) i will upload some decent pictures asap for you i will try your suggestions in post 68 next though.

[budm]

Re: LG LCD power supply

I would remove those inductors in post 68 to help isolate where the shorts circuit is.

[vinceroger69]

Re: LG LCD power supply

yes thats my first job tomorrow after ive took some decent pictures did you manage to find a psu schematic for this?

[budm]

Re: LG LCD power supply

yes thats my first job tomorrow after ive took some decent pictures did you manage to find a psu schematic for this?

No luck.

[vinceroger69]

Re: LG LCD power supply

u200 part number
3037cs
609p IR
ca098

[budm]

Re: LG LCD power supply

Nothing comes on up with those numbers.
Did you find the seller of that U200?

[vinceroger69]

Re: LG LCD power supply

no not yet was just looking myself the I R bit has a circle mark in it maybe the makers mark?

[vinceroger69]

Re: LG LCD power supply

budm its a 3037cs i missed the 7 out edited above post now on laptop not tablet.
http://www.alldatasheet.com/datashee...3037CSPBF.html

[vinceroger69]

Re: LG LCD power supply

This thread maybe worth a re read budm you helped in this thread same psu some good pictures etc
https://www.badcaps.net/forum/showthread.php?t=18218

[budm]

Re: LG LCD power supply

IRU3037, so basically the two inductors on your board are being used the same as shown in the diagram.
We just have to find where the shorts circuit is. We know that the shorts went away whe you lifted one leg of the jumper.