Repairing PSU FSP271-4F01

[jeremysaffir]

Re: Repairing PSU FSP271-4F01

I ordered both the BR and the MOSFETs, from different sites. BR arrived first, so I swapped it out. Fuse still blew. Guess we're waiting on those MOSFETs.

[jeremysaffir]

Re: Repairing PSU FSP271-4F01

Good news and bad news. MOSFETs arrived. I popped them in and flipped the switch... I saw a bit of a spark coming from the grounding wire I THINK. Not 100% sure on that. The TV happened to be plugged into a GFCI and turning it on tripped the kill switch, so I had to press the reset button to get power back to my outlet again.

The good news... the fuse didn't blow! Not only that, but the red LEDs on the main board are lit up! Looks like we've fixed the primary power issue!

However, the bad news is the backlight doesn't come on. It flickers a bit, but that's all.

What do you think? Does it sound like an indepenent issue to you, or could it have been something I did?

[selldoor]

Re: Repairing PSU FSP271-4F01

Check all cables firmly seated.
Perhaps try with a dvd input so you know you have pic and sound
When its all set up and plugged in but before pressing "on" can you report the voltages showing on the connectors from this board. Meter on 200 volts DC use a ground screw fro the black phttps://www.badcaps.net/forum/images/smilies/fruit.gifrobe near to the connector.
Then switch on and repeat.

Report exactly what happens when you switch on - what the power led does, what the back light does - any sounds clicks buzzes -.

When the backlight has gone off what does the power led do - is there still sound if there was sound. Get a flashlight and see if you can makeout anything on the dark screen.

[jeremysaffir]

Re: Repairing PSU FSP271-4F01

Check all cables firmly seated.
Perhaps try with a dvd input so you know you have pic and sound
When its all set up and plugged in but before pressing "on" can you report the voltages showing on the connectors from this board. Meter on 200 volts DC use a ground screw fro the black phttps://www.badcaps.net/forum/images/smilies/fruit.gifrobe near to the connector.
Then switch on and repeat.

Report exactly what happens when you switch on - what the power led does, what the back light does - any sounds clicks buzzes -.

When the backlight has gone off what does the power led do - is there still sound if there was sound. Get a flashlight and see if you can makeout anything on the dark screen.

PROGRESS!

I found a loose connection on a board I hadn't been messing with much.
When I turn on the TV, I get picture for about 1 second, then the whole screen goes blank for about one second. Then, picture comes on and stays on. I don't know if this is normal function of this TV or if this indicates a slight fault in a component.

In any case, I now have picture! And sound, too


However, I hear a constant, very loud buzzing sound from the main board.
And now, it seems like it's a crapshoot if I get picture at all when I turn the TV on. About 50% of the time I do. About 45% of the time I get the TV flickering between blue screen (no signal) and black. If it catches on the blue screen for a few seconds it'll start to render the input source and I'll have picture. About 2.5% of the time I get that flickering with no blue screen at all, and about 2.5% of the time I get a 600x860 or so block of scrambled, colored lines in the upper left corner and the rest of the screen is blue.
Whenever the screen goes screwy, none of the buttons seem to work anymore. Power button included.

Does that all make sense? I'm sure I could read into all of these clues a little better in the morning, I am very tired at the moment. That said, I'll be here for a while yet, ready to try anything you guys want to suggest.

Also, I've looked at the main board and all the caps look good, visually.

I have not yet seen the power LED do anything at all.

I'll have more information for you shortly, including meter readings as you instructed.

[tom66]

Re: Repairing PSU FSP271-4F01

I would remove and reseat the LVDS/T-Con cable as that can come loose and cause the symptoms you mention.

Is sound okay? (In other words... if the picture was perfect would you complain about the sound...?)

Sometimes the glue on the inductors dries out on the main board causing them to "sing" after some time. The fix is to apply a small amount of super glue to each inductor. Post a picture of your board and we can point them out?

[jeremysaffir]

Re: Repairing PSU FSP271-4F01

I would definitely complain about the sound coming from the main board. It is very piercing.

[tom66]

Re: Repairing PSU FSP271-4F01

I would definitely complain about the sound coming from the main board. It is very piercing.

What about sound from the speakers (try and ignore the main board) - mute the sound to get a reference noise level then compare to normal volume. Then post a pic of your main board so glue can be applied to fix it.

[jeremysaffir]

Re: Repairing PSU FSP271-4F01

I'm not sure what you're asking regarding the speakers. The speakers sound great, by themselves, as far as I can tell right now.


They sure didn't make this TV easy to service.



Uploaded with *************

The connector you see coming out of that bottom board makes its connection in the upper left quadrant of the board in the upper right.

here is a link to a very high res version of the photo:
http://img849.*************/img849/9117/img1108o.jpg

[tom66]

Re: Repairing PSU FSP271-4F01

I've marked coils with a red dot.

Does this thing use three main boards? Crazy... I've seen two before, never three...

Take a piece of newsprint or magazine and roll it up to create a tube - use this to locate the source of the noise exactly.

Also what is that parallel-port like connector at the top of the main board?

[selldoor]

Re: Repairing PSU FSP271-4F01

Not going to help but just out of interest do you know what the switch on the digital tuner board 150-21050 is for - perhaps it resets all the channels?

The insertion of the Gay gif in probe in previous post was unintentional I think I must have hit it in error as it bounces around at the end of the typing panel and I must have moved the mouse pointer to it as I am working on a laptop. I'll have to watch that or Ill be putting BS gif in posts ( some people reckon most of mine are anyway)

[pungo]

Re: Repairing PSU FSP271-4F01

Not trying to hi-jack here. I've been following this thread and found that Q3 & Q4 are shorted causing the fuse to blow. These parts are on order.

I also found that QS6 is also shorted but I can not read the part number on it as it has glue on it from an insulator on the center leg. I see OP listed it part number SUP85N15, but mine definitely doesn't have a part number that long.

The part number I can see on QS6 is N435AB and under that is FDPxxxx (where xxxx I can't make out due to the glue that's on it). I tried scraping off the glue but that removing and numbers there as well.

The power supply part number is the same as the OP PSU FSP271-4F01. Any help would be highly appreciated. I'm trying to fix this for my brother and it seems these power supplies are really hard to find.
TIA

[selldoor]

Re: Repairing PSU FSP271-4F01

Hi if you didnt remove all the numbers try cleaning with isopropyl alcohol.
EDIT
Please also confirm the make and model of the TV. IF it is the same as the op
We can help a lot more if you please post good clear pictures of the whole chassis, and then pictures of each board, front and back and close up of connectors, (max resolution 2000x2000 and 2MB) using the manage attachments button, which is found by clicking "go advanced" under quick reply.

Please do not post inline and offsite as they slow down the loading of pages.

Examples of what is needed
https://www.badcaps.net/forum/attach...1&d=1290283049

https://www.badcaps.net/forum/attach...7&d=1280167246

It will be useful if you can say what the supposed fault was and a bit about yourself - skills tools etc

If a different set please start a separate thread.

[pungo]

Re: Repairing PSU FSP271-4F01

selldoor, thanks for the reply. Unfortunately I don't have the TV set with me, my brother removed the power supply and asked me to take a look at it to see if I could fix it. The fuse on the power supply blows immediately, even if not connected to the TV. I used to be a bench tech back in the 80s repairing complicated 300 plus chip count telecommunication circuit boards to component level. I can remove and solder these basic electronic components of this type of power supplies.

The TV is the same as the OP, Olevia LT42HVI 42" LCD TV.

After looking at QS6, I see QS3, QS4, QS5 which are all part number SUP40N10. I cleaned up the QS6 I pulled and looked at it with a loop and was able to make out the part number as a Fairchild FDP2552.

I wonder if the p/s manufacturer replaced the Fairchild FDP2552 with the SUP85N15 as it looks to be a higher current MOSFET? I guess I should order the Fairchild FDP2552 just to be safe.

Here is a picture of the power supply from the OP, I have outlined the MOSFETs and labeled them.

[selldoor]

Re: Repairing PSU FSP271-4F01

It has been said a number of times on here that posting a picture of another board is like going to the doctors when you are unwell and taking your brothers X-rays along to help with the diagnosis.

Does the fuse still blow with the mosfet out?

If so did you test Q2

[pungo]

Re: Repairing PSU FSP271-4F01

selldoor, That is a great analogy, I currently don't have my camera, so I couldn't take a picture. I only posted the OP pic so that you could see the location of the mosfets. I will post pictures of my actual p/s once I get my camera back.

I tested Q2 for shorts with a DVM to make sure it was not shorted I did not pull it or test the operation. With Q3, Q4 and QS6 removed the fuse does not blow. I did remove the bridge rectifier and it tested good, then put it back before powering it up.

Since I know know the part number of the mosfet, I just need to order the Fairchild FDP2552 at location QS6. Looks like it should be under $10 shipped.

I would just hate to replace the 3 mosfets and have them blow again, so I'm trying to trace the path from the mosfets to see if anything down stream is fried that caused them to blow.

[tom66]

Re: Repairing PSU FSP271-4F01

One trick some TV technicians use is to insert a 60W or 100W filament lamp in series with the TV.

If there is a short the lamp will stay lit, but if there is no short the lamp will brightly glow for a short time (while the main cap charges) and then go out or go dim.

It will also stop your new FETs from burning up most of the time. Usually the TV won't operate properly with the lamp in series though so the final test would have to be without one.

[budm]

Re: Repairing PSU FSP271-4F01

You should build one of this so you will keep blowing up your new parts as Tom suggested.
https://www.badcaps.net/forum/showpo...3&postcount=12

[jeremysaffir]

Re: Repairing PSU FSP271-4F01

Update for my TV:

My screwy picture was just a loose connection. I now have consistently good picture and sound (although, when the TV first turns on it does do something a little screwy but then it's fine)

However, there is still a high-pitched sound coming from, I believe, L2. It is the Yellow component near the fuse. I don't know what L2 is. Do any of you?
Also, if the TV is on long enough, L2 begins to give off a burning smell.

[budm]

Re: Repairing PSU FSP271-4F01

That is the PFC Voltage booster inductor.
What DC voltage do you get on that big filter cap when the TV is OFF and when the TV is ON?

[jeremysaffir]

Re: Repairing PSU FSP271-4F01

I'll have to get back to you on that. I was messing with it, and without going into details, I managed to blow the fuse again. Last one I had on hand, too, so I'll need to go out and buy more tomorrow, if I can find a place that's open.