Megmeet MLT666 R2.8 cockroach short

[mikoz]

Hi,

I'm seeking some advice as where to start with this horrendous psu.
Grabbed this 32" "Space" LCD for free from a council cleanup and would like to give it a chance.

DEAD. no lights nothing! Opened it up to find an infestation of biblical proportions. After blowing it all out with the compressor I pulled this psu and found a roach charcoaled to the board at the position circled below.
Cleaned the area up with alcohol and found a few burnt smd resistors.
The fuse f1 was blown also so I swapped in a new one for visuals and bang, blew straight away

So far I have changed all the caps except for the big filter with new mixed panasonics for startups, Yageo and Jackson for secondaries.

There are a few resisters burnt (R43 & R14) on the solder side that I cannot read values of, and I have circled them in the picture below just incase someone has this same board.

Z2 reads open both ways (should I be taking this out of circuit?), and R74 (0.5 Ohm 1%) seems to have a chunk of pink missing.

If somebody has the time to help me with fault finding I would be incredibly grateful.

[Mrx3750]

Re: Megmeet MLT666 R2.8 cockroach short

OMG I think I recognize that power supply! They're used in TV's from 26 to 32 inch, Chinese branded TV's. I never had one fail on me so I don't have much experience working on them.

I will say that if you find a TV that has the model L2626 or L3226, regardless of brand name, it likely has this power supply.

[mikoz]

Re: Megmeet MLT666 R2.8 cockroach short

Yeah I haven't come across one before, the model of this set is LTV3268B. Its a very cheap looking chinesy logo too. It has a fairly decent condition chi mei screen and bezel size though I may lose the branding?

[Mrx3750]

Re: Megmeet MLT666 R2.8 cockroach short

Well, no promises, but I may have a TV here with that power supply. If it's the same one, do you want pics of anything?

[mikoz]

Re: Megmeet MLT666 R2.8 cockroach short

That would be fantastic if you wouldn't mind and have a little time? I really just need a close up of the area i circled in picture 4, or even just the values for those two resistors if a picture is too difficult.
Cheers
Mick

[Mrx3750]

Re: Megmeet MLT666 R2.8 cockroach short

Okay, the power supplies aren't exactly the same. Still maybe these pics can help?

I tried to get closer ones, but the camera flash just whited everything out.

[budm]

Re: Megmeet MLT666 R2.8 cockroach short

This is pretty cheap power supply:
http://www.shopjimmy.com/catalogsearch/result/?q=MLT666

http://www.shopjimmy.com/megmeet-mlt...upply-unit.htm

[mikoz]

Re: Megmeet MLT666 R2.8 cockroach short

Thank you kindly, it is quite a different layout huh? But from looking at yours it appears what I thought was R14 is in fact R44 and yours is a 470 so 47 Ohms . Mine looks almost as if that is what it had written on it but I get a reading of 558 in circuit so I may take it out. R43 I cant find on yours though and looks to have a 4 digit code?

[mikoz]

Re: Megmeet MLT666 R2.8 cockroach short

Thanks Budm, I did have a look for an Australian seller on ebay for one but he wanted $50 + 20 freight.
I'm more inclined to troubleshoot & repair this thing. As there really is no education in a board purchase.
But if the failed components end up getting too exhaustive, I'll admit defeat and just buy a board
I found another post with a schematic, but there aren't any resistor values on that either that I can find.

[mikoz]

Re: Megmeet MLT666 R2.8 cockroach short

Searching electrotanya I have found a schematic with values for this board. It appears they are both (R43 & R44) actually 2R20 coded so 2.2 Ohms is that right? And are they supposed to be 2w tolerant?
Ive attached the schematic for others to ponder. Its for the MLT666a though but looks identical.

[Glitcher]

Re: Megmeet MLT666 R2.8 cockroach short

Since the main fuse is blown some common things to check would be the bridge rectifier, mosets, and diodes on the primary side.

[tom66]

Re: Megmeet MLT666 R2.8 cockroach short

Likely 2.2R 0.125W 1206 size.

[mikoz]

Re: Megmeet MLT666 R2.8 cockroach short

Hi Glitcher,

So BG1 (slanted corner) would be the bridge rectifier?
In diode mode with the black probe on the screw I get;
1(+)=1, 2(~)=0.01, 3(~)=1, 4(-)=0.01
with red on screw I get:
1(+)=513, 2 (~)=0, 3(~)=558, 4(-)=0

Does that make any sense?

[attainteddragon]

Re: Megmeet MLT666 R2.8 cockroach short

hey mikoz, test the bridge in diode mode. but measure pin 1 to 2, 1 to 3 and so on till all combinations from all pins are done, then do again with leads reversed. post your readings from there.

[mikoz]

Re: Megmeet MLT666 R2.8 cockroach short

Z2 = 0 (shorted) both ways.
D3 Red on screw I get 565 (left) 513 (right) Black on screw I get no continuity from both legs. (I think this one has to come out to test)
Z4 = 564 & no cont.
Z9 = 595 & no cont.
Z1 = 0 both ways.
D8 = 478 & no cont
L5 = 0 both ways. (what is that?)
D4 = 488 & no cont.

I see a pattern forming...

[mikoz]

Re: Megmeet MLT666 R2.8 cockroach short

Bridge red on 1
1-2=1 1-3=1 1-4=1 2-3=559 2-4=0 3-4=1
bridge black on 1
1-2=514 1-3=568 1-4=514 2-3=1 2-4=0 3-4=559

I hope that's ok?

[attainteddragon]

Re: Megmeet MLT666 R2.8 cockroach short

i take it that your meter shows ol as a 1, if so, it is all good.

[mikoz]

Re: Megmeet MLT666 R2.8 cockroach short

Yeah it's pretty cheap.
What's the L designation though? It looks like a diode.

[attainteddragon]

Re: Megmeet MLT666 R2.8 cockroach short

l is normally an inductor. just ohm it to test.

[mikoz]

Re: Megmeet MLT666 R2.8 cockroach short

Is there a test for the mosfets I can do in circuit seeing as though i have shorted zeners, or do they need to be loose?