Samsung 42 Plasma Wont turn on PSPF411701A

[anotherdude]

Re: Samsung 42 Plasma Wont turn on PSPF411701A

Those two FET's have had a crisis, to me they appear to be on the Hot side of the VA supply, I wouldn't be probing around there with a meter, in particular any voltage on those is in relation to the hot ground only. They wont fail for no reason either.

thats my point from the start there must be a underlying fault for them to blow like they did, even if the tv has power going to it those fets should be recieving power and the 5.3v test point on the board recieve next to no power on everything i've tesed on the board it all reads below 1 volt including the fets

not sure on where to go from here, other than get a new board which is looking at £60-70 which just isn't worth it already got £55 into it

[tom66]

Re: Samsung 42 Plasma Wont turn on PSPF411701A

FETs can blow on their own accord -- due to high running temperature or poor design. However, when they fail, they usually damage other components.

[Clydeuk]

Re: Samsung 42 Plasma Wont turn on PSPF411701A

Any chance of a close-up of those two connectors on the bottom right of your first picture? The black one in particular? And any voltages you have taken from there?

[Clydeuk]

Re: Samsung 42 Plasma Wont turn on PSPF411701A

Sorry meant last picture not first

[Clydeuk]

Re: Samsung 42 Plasma Wont turn on PSPF411701A

5 volts must be going to the main board, or you'd have no standby light, if the light goes out when you press the button on the remote then it suggests that part of the main board is doing something as well, so it's whether the "on" signal is betting back to the supply to bring up the running supplies. Unfortunately there's often a lot of protection circuitry that will shut it all off if a problem is detected, but generally the VS and/or VA will come up very briefly before the shut off, usually enough to measure. For what it's worth I'm wondering if this was originally the dry joint problem that was mentioned above (very common), and either a poor repair caused this damage, or the other known common fault (which you've fitted the kit for) has shown itself.

It's not a supply that I have direct experience of most designs follow the same idea, give or take protection features etc.

[Leeland out]

Re: Samsung 42 Plasma Wont turn on PSPF411701A

I have to agree with all the previous posts, this is a great forum one of the best I have seen
My problem is slightly different, I have an issue alone the same theme, my Samsung plasma has the blue standby led but does not attempt to turn on. Ie no clicking. When it turns on (not very often) it works well with no issues. It just getting it to kick out of standby. I have checked the on switch it is working correctly, not stuck on etc. psu board seems fine I also checked pin 10 and 7 of the connector, pin 10 5.3v pin 7 not changing when I click the on button. Stays at 2.5v . Psu board does have a slight high pitch noise sounds like transfer windings could be red heron. Any ideas where to check now? I am guessing main pcb or psu as the power button pcb only has a few components does anyone know if this is a common fault? Any advise welcome.

[XtraTN]

Re: Samsung 42 Plasma Wont turn on PSPF411701A

Hey looks like I'm working on the same exact PSU as yours. Mine is just making a clicking sound when plugged in. I was wondering what are the values of the resistors RX833, RX802, RX803, and RX832?

[jbullard23]

Re: Samsung 42 Plasma Wont turn on PSPF411701A

I've got an issue with a Samsung plasma, also, but I'm leaning towards power supply issues. I'm new to the whole forum community. I've never posted on a forum before so I'm not sure where to post my question and describe my problem for help. I sure don't want to post on someone's thread and upset anyone. That being said, could someone point me in the right direction?? My TV model is PN59D550C1FXZA. Thanks!!

[jbullard23]

Re: Samsung 42 Plasma Wont turn on PSPF411701A

I forgot to mention that the TV has no picture or sound. Just didn't want to get too detailed until I know I'm in the right place to do so.

[nogger]

Re: Samsung 42 Plasma Wont turn on PSPF411701A

HI, i repair these PSU's on a regular basis as part of my business .Lots of people have helped me in the past on here so i'm hapy to advise you on this.

What you have there is a typical PSU problem on these plasma's. The soldering of the 2 FET transistors is often very poor during manufacture & over time they develop dry joints on the FET pins & they blow. Just replacing the FET's is not enough as there are almost certainly several surface mount components blown & quite likely the chip & smd components on the small daughter board that stands up next to the FETS.

You need to check with the board by itself on the bench if you get 62 DC volts on the Va test pin. to switch the PSU on you need to short the pin marked PS_ON to gnd. If there's no 62v you wont get any 5 or 12 volts. Lack of 62 volts means the chip isn't pulsing the FET's, AND/OR the FETS are blown AND/OR the fuse is blown so there's no DC to the FETS.

I'm not at my w/bench at the moment but will dig out some circuit ref's for the parts to check. One other thing is that in blow ups like this it is not uncommon for parts of the copper tracks to lift off the board so often you have replaced the faulty parts & overlook missing track. Take a good look at teh board & see if tere's any missing track.

Clydeuk , the PSU generates 5v Standby voltage seperate from the circuitry thats failed in this case so you will get a standby light on the TV. but unless the chips pulsing the FET's & the 62v is present you wont have the regular 5volt & 12 volts supplies.

Graham

[nogger]

Re: Samsung 42 Plasma Wont turn on PSPF411701A

Ok just read back over this thread & the information on the Preher blog that was linked to earlier pretty much sums up this problem (http://preher-tv.blogspot.co.uk/2010...-repaired.html )

I would unsolder the daughter board that sits just behind the heatsink the FET's are mounted on & go over that board with a meter. Check all the transistors/diodes etc on that board . If in doubt remove the other daughter board (mark them first) & do comparison readings as they are identical. For the sake of a few pennies i would change the chip anyway (you can get it at RS Components stock # 516-5691 ) or if stuck contact me.

With the boards still out i would go over the smd resistors/diodes on the PSU board referenced in the Preher blog post & check for shorts. Don't forget that the 2 resistors RX833 & RX802 are in parallel so you should get a reading of approx 10-11 ohms, same goes for for RX803 & RX803. Once you are happy the daughter board is ok & the smd parts on the mainboard are ok then replace the FET's & daughter boards. When you replace the FET's scrape back some of the green solder resist around the pins to expose a larger copper area to solder to & make sure your connections are sound (meter them).

Check the white fuse F803 is good & apply power. At this point all you should have is 5v standby & there will be NO clicks. Look at connector CN807 & you will see pins marked STBY, check for 5 volts on that. Now take a small screwdriver & temporarily short the pin marked PS_ON to the pin next to it marked RTN, when you do that the relays should click & you will be supplying the FET's with DC (lots of it). If at this point the FET's have not blown again (which means you missed something) , then measure for 62 volts on the Va test pin on the board.

If you have that 62 volts then your 12 volts & 5.3 volts should also be there, try that & see how it goes.

I have attached snippets from the service manual showing the circuitry round the FET's & the daughter boards so you can get an idea whats happening.

WARNING: You need a good iron (not too hot & good solder skils to work on the daughter boards & smd parts otherwise you end up with lots of lifted tracks & solder blobs. Also these boards carry very high voltages, you must be careful when working on them. A finger in the wrong place will ruin your day, believe me i have had a few ruined days. If you don't feel confident & safe when working with mains voltages then either get a new board or send it somewhere for repair. I accept no responsibility for absolutely ANYTHING as a result of you following any of the above :-)

Graham

[Brass eagle]

Re: Samsung 42 Plasma Wont turn on PSPF411701A

I've had problems with the same board,but mine was clicking all the time and not coming on,i spent a lot of time trying to replace caps ect, my caps looked ok ,I didn't try replacing the qx801 or qx802 parts as this looked tricky to me as my skills are limited,I eventually bought a recycled board from ebay and it works ok now,I have kept my old board and I will eventually buy the qx801 parts and try it out,it's all about experience to me ,so I can learn something new,this site is very helpful

[gizmouk]

Re: Samsung 42 Plasma Wont turn on PSPF411701A

A friend of mine asked me to a tv with this board. The tv would turn on the after 30 seconds or so it would turn off, then turn on again. I opened it up to see two capacitors bulging. I replaced those and tried again. This time it stayed on again for about 30 seconds then turned off and started to click. After finding this page and reading from http://preher-tv.blogspot.co.uk/2010...-repaired.html I decided to resolder MOSFETs QX801 and QX802. I turned the tv back on and it worked! Tested it running for half an hour and it stayed on. Thank you for the help on fixing the tv!

[flocko]

Re: Samsung 42 Plasma Wont turn on PSPF411701A

Take the board out of the set to test, with mains supply you will 5vstby on the bottom right connector first pin on left(as you have blue stby light ) pin 4 PS on you need to put to ground (make low) the relay will click in and all the voltages apart for Vs should now come up (check test points) if these are showing make Vs On pin2 (make high )using the 5vsby (pin 1) and a 500ohm resistor, this should bring up the Vs test and report back to us what you find Flocko