Samsung PN42C450 B1DXZA Doesn't Power On

[Eaglecrest]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

Presumably the TV problems started with blown transistors on the X Main. Then while checking further I saw smoke on the left side of the TV from the back that appeared to be coming from the Y Sustain board and the PSU is damaged. All three could be separate issues, but I would think one would have to suspect a connection. A failed X Main should not cause the Y Sustain to fail, but would a failure on the Y Sustain cause the PSU to also fail? If so what might cause this and where?

Perhaps most importantly, how do I determine if the Y Sustain is still good and what the issue with the PSU is?

[Andrew F. Ali]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

A failure in the X-Main or Y-Main will not cause a PSU/Vsus failure. Neither would a failure in the Y-Main cause a failure in the X-Main and vice versa.

[Eaglecrest]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

I am a neophyte just trying to gain knowledge. I recognize I am trying to drain an ocean through a straw, but one has to start somewhere. So this is a project where I am trying to understand why as much as just fix a problem.

My current understanding is that each board/subsystem is an independent supporter of other subsystems. Thus if a board stops working then that in and of itself will not cause another board to fry; however, it would seem that if something on one board burns out it might cause a condition - short, loss of current/voltage regulation, etc. that could fry something on another board. Is that an inaccurate understanding?

[Andrew F. Ali]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

In my years of PLASMA TV repairs, I have not come across any situation/event like that. If a component goes bad the set would shutdown and not try to stay working which could cause, yes another board to burn up. If that was the case then when one component an aboard goes bad it would cause a chain reaction of breakdowns which would be catastrophic and render the TV to costly to repair.

[vinceroger69]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

when you say - I saw smoke on the left side of the TV from the back that appeared to be coming from the Y Sustain board have you checked the y sustain board for burnt/shorted parts or are you just replacing this board as smoke coming from a board is never a good sign and needs investigating.

[Eaglecrest]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

Vince,

I would prefer to repair any boards if possible, but I do realize that becomes more difficult as I need remote assistance. I did look at the Y board looking for signs of burnt component and or connections and didn't see anything that looked like it was damaged. I didn't hear anything like a pop or sizzle, just noticed some smoke like after you blow out a cake candle. Not heavy nor continuous, but clearly noticeable. It dissipated rather quickly for what it is work. Since clearly on the left side of the Y Sus board and there is a large heat sink blocking movement from the interior of the TV it could not have come from the PSU or I would have noticed it trailing back that way. It came straight up the side of the board.

I have transistors coming to try and repair the Z Sus board. I don't know for a fact that Y Sus is bad, but smoke usually isn't a good thing. Since the PSU now seems to be bad and I can't test Y Sus's effects on PUS is there anything I can look at to determine if the Y is bad?

On the PSU we know that power comes on Vs for a few seconds when it starts and when powered up. This voltage then shuts down. One thing I did notice was that it quickly drops to zero, when Vs was stable it would take a few minutes to fully discharge. We also know that the logic board fires up and the main board fires up.

What is my next step on the PSU?

[Eaglecrest]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

When replacing the two transistors on the X Main board how do I deal with mounting to the heat sinks?

• Is the thermal paste the same that is used for mounting cpu's to a motherboard?
• Do I need to scrape the old paste off?
• Or do I just place the transistor onto the paste that is left over on the sink?

Any other advise for the replacement effort?

[Eaglecrest]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

Ok, got the transistors and would appreciate advice on how to replace them, specifically dealing with the paste between the transistor and the heat sink.

[geeforce]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

I used up some cpu thermal paste... I need to get more universal stuff for these repairs though. I would think its ideal to apply more thermal paste.

[Eaglecrest]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

Got the X Main off to try and replace the FETs. There is a grey bar across the pins on the bottom. Looks like I need to pry this off, but not sure what it is and also assume I need to put it back when I am done. How delicate is this stuff and is there a suggested way to remove it (picture attached). Also the two FETs that need to be replaced don't have any solder on the top side of the board except for the forward legs which look to be soldered on both sides. Why is that?

Lastly, what is the point of the daughter board? It seems to just be an extension to move the connector further down and has a single cap. Also it seems to snap in, but not sure how to separate it.

[tvtimmy]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

The gray bar is sort of a heatsink. Just peel it off and then stick it back on. The pin with the solder on top goes through a rivet hole. That one will be the last one you should remove( heat up and yank out the fet). Then clear out the hole. The daughter board is just an extension.

[Eaglecrest]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

I got the transistors and tried to remove the blown ones, but can't seem to get them out. I am using an inexpensive 30 W iron and the solder doesn't seem to melt. I have tried adding fresh solder, but even when it does melt a bit it seems to hard immediately once the iron is removed. Does this mean I am working with lead free solder? Attached are some pictures of the pads.

Also my vacuum solder sucker won't lock anymore. I have taken it apart and can't seem to find the problem. Outside the sleeve it will lock in position, but when reassembled it won't catch the plunger. Any thought here?

[tvtimmy]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

Buy or borrow better tools.

[Eaglecrest]

Re: Samsung PN42C450 B1DXZA Doesn't Power On

Buy or borrow better tools.

Got to start somewhere.

Anybody have ideas on the solder sucker?