Westinghouse L2046NV Mosfet 40T03GP Wanted!

[EGuevarae]

I have two LCDs, one Acer and one westinghouse. They are 19" and 20" respectively, and share the same power supply. I got to keep one if I fix the other one, so I want (need!) to fix them both. One is already working after a recap job, but the other is dead : no backlight.
I was checking around the board, and came across these two mosfets, one for each transformer. One has continuity over its three pins (both ways) and the other one does not behave in the same way. I was looking for a replacement and I have found none. Any idea?
Here's the datasheet I found. Please help me to get a 20" LCD (I know I already have one, but you can't beat the price : free! I couldn't help it.. )
I have some pictures if needed.
Thanks in advance guys.

[Toasty]

Re: Westinghouse L2046NV Mosfet 40T03GP Wanted!

These look to be a fairly close and perhaps better match:

IPD135N03L G
http://www.mouser.com/Search/Refine....ord=IPD135N03L

IPS135N03L G
http://www.mouser.com/Search/Refine....ord=IPS135N03L

Datasheet: http://www.infineon.com/cms/en/produ...ml?q=ipd135n03

Toast

[EGuevarae]

Re: Westinghouse L2046NV Mosfet 40T03GP Wanted!

Do you recommend to change them both or just the shorted one?
Also, I changed 2 bulged CapXons 25v 220uf only (no more caps, ordered from DigiKey already). Is there any reason for the MOSFET to short? It was the top one (see Pic):

[PCBONEZ]

Re: Westinghouse L2046NV Mosfet 40T03GP Wanted!

I would recommend replacing both as they usually work together and changing one without the other may throw something out of balance.
Mind you that's without tracing the circuit out, just a good practice in general with MOSFETs and other kinds of mirrored or opposing transistors in a circuit.
.

[EGuevarae]

Re: Westinghouse L2046NV Mosfet 40T03GP Wanted!

I would recommend replacing both as they usually work together and changing one without the other may throw something out of balance.
Mind you that's without tracing the circuit out, just a good practice in general with MOSFETs and other kinds of mirrored or opposing transistors in a circuit.
.

So in general it would be a good idea to replace them both, as when a headlight goes out in your car and you change them both also....
OK, I am there anyway, and at less than a dollar the piece, it would be a preventive action. less than $10 for caps and MOSFETS for a 20" LCD is a reasonable cost

[PCBONEZ]

Re: Westinghouse L2046NV Mosfet 40T03GP Wanted!

This doesn't apply to Power MOSFET because the temp coefficient is different.

There is a condition called Thermal Runaway that can cause problems with matched transistors.
Thermal Runaway - Temp goes up, junction resistance goes down, current goes up, so temp goes up more, and around back to the beginning, over and over.
-
It is a major concern when transistors (most all kinds) are used in matched pairs.
[Especially in parallel.]
-
If you un-match the parts with a replacement minor differences may cause more of the load to be taken by one of the transistors instead of it being shared equally.
The loaded one will heat more/faster which causes it to take even more of the load then it may 'runaway' and try to take the entire load. If it does it will overheat and burn out.
When it goes the other gets the entire load dumped on it suddenly and it will usually burn out too.
.

[Toasty]

Re: Westinghouse L2046NV Mosfet 40T03GP Wanted!

...change them both or just the shorted one?...<snip>...any reason for the MOSFET to short...

I wouldn't order anything until I had those 2 out of circuit. I kinda a doubt they're bad. Then you can test and be sure that you have a difference between them. Fortunately they're not the ones with the tab soldered down. Which makes me think they are a bit of overkill in this circuit, as they're rated 30W and 28A continuous and not even heatsinked.

As I said in another of your back light posts, the outputs of these devices are typically across the primaries of the ballast/transformer. You are always going to read shorted until they are clear of the circuit.

Then again, for 58 cents a piece, who cares!

Toast

[Toasty]

Re: Westinghouse L2046NV Mosfet 40T03GP Wanted!

I'm confused.

You suggest that he change both devices, he says he's going to, then you say it doesn't apply here?

Or, are you disagreeing with his analogy of changing them similar to headlamps? "I'm there already, I might as well", instead of the theoretical reason, "They may be electrically mismatched which can be a problem as such...".

Temperature coefficient of...?

While I can agree on matched pairs or sets of devices, especially from years ago in power RF output stages and high end audio equipment, I don't see that much these days. Is this because of better QC and manufacturing practices?

For one, how will these be a known matched pair? Usually they are (or rather were) sold as such from the manufacturer and typically were 2 in a bag. Or, if an entire run was the same, there was a color dot or two to show that. What's not to say one of these (replacements) is Monday's run and the other is Thursday's?

Toast

[Toasty]

Re: Westinghouse L2046NV Mosfet 40T03GP Wanted!

Also available from Digi-Key:

IPD135N03L: http://search.digikey.com/scripts/Dk...35N03LGINCT-ND

IPS135N03L: http://search.digikey.com/scripts/Dk...S135N03LGIN-ND

[PCBONEZ]

Re: Westinghouse L2046NV Mosfet 40T03GP Wanted!

>> You suggest that he change both devices<<
Yes I did.

>> then you say it doesn't apply here? <<
No I didn't.
I said Thermal Runaway doesn't apply to Power MOSFETs.
Their temperature coefficient is + vs - as with most other transistor type ICs.
On Power MOSFETs when Temp goes up, junction resistance goes up, current goes down.

Thermal Runaway is just one example of why keeping matched parts matched is a good idea.
It was general discussion and , as I said, not specific to this circuit.

.

[EGuevarae]

Re: Westinghouse L2046NV Mosfet 40T03GP Wanted!

I wouldn't order anything until I had those 2 out of circuit. I kinda a doubt they're bad. Then you can test and be sure that you have a difference between them. Fortunately they're not the ones with the tab soldered down. Which makes me think they are a bit of overkill in this circuit, as they're rated 30W and 28A continuous and not even heatsinked.

As I said in another of your back light posts, the outputs of these devices are typically across the primaries of the ballast/transformer. You are always going to read shorted until they are clear of the circuit.

Then again, for 58 cents a piece, who cares!

Toast

As far as I remember, I tested both PSUs, and each of the ICs on board, then pulled out the "bad" one and tested it outside. I will retest it just to be sure, but I remember that I saw a diode inside the IC diagram, and the diodes have to be checked either out of circuit or with a pin lifted (so they are basically out of circuit). Again, I'll recheck it (them, as I removed the pair thinking from the very beginning in replacing them both if found and if $$ would allow it).

And it is nice that you follow up on people ("As I said in another of your back light posts ...") rather than just throwing an answer/tip (even if it is a correct one, is nice to know that someone follows up).

And regarding the analogy of the headlights, I tend to use that kind of things to make things even clearer : I know that some of my questions might be electronics-kinder-grade but I am a computer technician that mainly developed software and never had to mess with electronics, and this sort of analogies help me a lot. Have you seen the movie Philadelphia , where Denzel W. plays an attorney that has a motto like "explain it to me like I was six years old ....". Well, that's my approach here

But so far I've repaired many (more than 25 now that I check my notes) LCDs and helped others to do it, so, as it is said, so far, so good.

[EGuevarae]

Re: Westinghouse L2046NV Mosfet 40T03GP Wanted!

Also available from Digi-Key:

IPD135N03L: http://search.digikey.com/scripts/Dk...35N03LGINCT-ND

IPS135N03L: http://search.digikey.com/scripts/Dk...S135N03LGIN-ND

Out of stock until first week of April. Better order them from mouser.

[Toasty]

Re: Westinghouse L2046NV Mosfet 40T03GP Wanted!

>>I said Thermal Runaway doesn't apply to Power MOSFETs.

Ahhh! I thought you were replying to the previous post(s). The lack of a - or : at the end of the opening line is what threw me off. So the entire statement was regarding thermal runaway. Gotcha!

Toast

[EGuevarae]

Re: Westinghouse L2046NV Mosfet 40T03GP Wanted!

Monitor fixed. Replaced both MOSFETS, a SMD fuse beneath the inverter area, and now I am browsing using it on a dual display configuration.

[jepongski]

Re: Westinghouse L2046NV Mosfet 40T03GP Wanted!

hi can you tell me which SMD fuse you;ve replaced coz i got the same power supply. and the same problem.

[bullwinkle]

Re: Westinghouse L2046NV Mosfet 40T03GP Wanted!

I also have the same problem on my Acer 19" LCD. Got to try soon what I learned here

[PlainBill]

Re: Westinghouse L2046NV Mosfet 40T03GP Wanted!

hi can you tell me which SMD fuse you;ve replaced coz i got the same power supply. and the same problem.

The fuse is F200. As noted it's a SMD fuse. I replaced it with a 4 Amp fuse.

PlainBill

[bullwinkle]

Re: Westinghouse L2046NV Mosfet 40T03GP Wanted!

Monitor fixed. Replaced both MOSFETS, a SMD fuse beneath the inverter area, and now I am browsing using it on a dual display configuration.

The same procedure and my ACER 19" LCD monitor is now alive and kicking! Many thanks!

[bullwinkle]

Re: Westinghouse L2046NV Mosfet 40T03GP Wanted!

The fuse is F200. As noted it's a SMD fuse. I replaced it with a 4 Amp fuse.

PlainBill

Yes I also replace this fuse. My ACER 19" LCD monitor is now alive and kicking. Many thanks.

[bullwinkle]

Re: Westinghouse L2046NV Mosfet 40T03GP Wanted!

Oh, forgot to mention i do recap all the big value caps from 220uf up.