Electonics Gurus Unite! What kind of transistor?

[phaxmohdem]

I have a Sony PFM-42B1 Plasma Flat panel Monitor that is not working. It will start to turn on but as soon as power is sent through the system, one transistor makes a "decharging" noise.. (Starts high pitched and quickly lowers in tone... noise lasts a fraction of a second) Teh fans turn on but once the noise is made then spin back down and teh unit keeps doing this several times before it gives up and you have to press the power switch again to try and power it up..

I took it to the TV repair expert at the television station I work for. HE parted it out over a whole weekend, hand tested all the Caps and transistors and came up with one that he thoguht was defective. Interestingly enough that is the one that makes the decharging noise.

Linky to Picture (All innards)

Linky to Picture (This is the believed bad Transistor)

The transistor in question has the larkings "L349" on it below that is marked "1B". I looked through an electonics supply manual and could not cross reference this exact part number to anything.

Is there a way to figure out what kind of transistor I need to replace this with? Other suggestions? I know there are some smart people here when it comes to this sort of thing, and I really need your help. I'd love to use my display. Thanks

 

[MetalStorm]

Why don't you send it back to get repaired? Unless you've already voided the warrenty by opening the thing up, in which case... lol!

 

[PsYcHoCoW]

Is L349 written straight on the transistor? Googling around with that doesn't tell me anything, so I'm doubting that this is the part number..

To find a replacement...
In the simplest case, which is when the transistor is used in switching mode (non linear - 1 or 0), it can be replaced with another one of the same type. When used in linear mode, you may need a precise gain and a precise saturation voltage, and thus a precise transistor model.

If the transistor is bipolar, you can determine its type this way: http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trantest.html

Once you know the type of transistor, you need to know what voltage and current it needs to support. If you're lucky, a simple TIP120/TIP127 will do the job.


It's kind of hard to find a replacement without knowing what it needs to replace... Ideally a front shot of the transistor would help. Sometimes there's interesting info to be seen... http://www.stquentin.net/resist/im/to220.JPG

 

[Megamixman]

First of all that large heatsink gives us the premise that it could even be a voltage regulator. There are 3 pin voltage regulators and that PCB area also seems to be a power supply PCB, or at least power regulation. I doubt a simple TIP120/TIP127 will work. Look at the size of that heatsink; it has to be a high power transistor.

http://www.wehaveparts.com/
Seems to have parts for your Plasma and it also has a service manual which should help you identify that, but it is $170.

 

[phaxmohdem]

Thanks for the tips. I may be a voltage regulator. It has three prongs on it. As for the warranty thing, I purchased it used with no warraty coverage...

A frontal shot of the transistor/regulator probably wouldn't help much, there is seriously nothing else written on it other than what I described in the first post.

If I were to yank a similar looking part out of a computer power supply and replace it with that.. could that completely screw things up?

 

[Megamixman]

NEVER TRY SOMETHING THAT LOOKS SIMILAR! They could be greatly different and have the same packaging. Something as small as the difference between a normal switching transistor and a MOSFET could kill most of everything in your Plasma, and I mean KILL! Besides that isn't the highly technical thing to do. I really don't know what to say, besides buying the service manual. That should have the type of transistor that is so that you could replace it with a similarly spec'ed transistor or voltage regulator if it is one. See if you can find the service manual online.

 

[PsYcHoCoW]

A lot of different parts use TO220 cases... their pinouts and uses vary. Since there's not much info on the transistor itself, it will be hard to determine the use/type of that IC without the schematics. Schematics can't be "found", you have to be an authorized service center in order to get them...

 

[phaxmohdem]

OK.... well I definately won't replace it myself then with something similar. I may call sony and see if they offer that part, or perhaps even that whole board, and see what prices are that way. IF they are too high, I may just put it up on ebay and get it over with. Thanks!

 

[bharok]

on the transistor there is a heat sink screwed on
if u ar able to somehow remove his heatsink you might be able to find the model number.
look up the model number on google
or
digikey.com

 

[Yossarian451]

The heatsink and the "L" make me really belive that is a power regulator.

 

[RaynorWolfcastle]

That looks like a regulator or a power FET to me, but it's difficult to tell. It's surrounded by large caps and has a huge heatsink, so it's almost certainly some sort of power IC.

Can you make out a logo on the chip? You might be able to find it using the manufacturer (National would have a circled N on it, Analog Devices would have an arrow on it, etc.)