42" Samsung Rear Projection TV

Discussion in 'General Electronics Chat' started by tom66, Jul 27, 2011.

  1. tom66

    Thread Starter Senior Member

    May 9, 2009
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    Got this beast for free :).

    Model #SP42W4HB

    The problem with it is that it apparently only works occasionally. I haven't yet got it to power up. When switched on, it makes a buzzing sound for a second, then the standby LED blinks on and off. It does this repeatedly.

    I then looked at the blue CRT PCB. There was a bit of burning on the PCB and I noticed when turned on, a puff of smoke would come from here, or the nearby driver IC. Dead driver IC?

    I tried disconnecting the blue PCB. Now the TV powers on briefly and makes the Samsung beep. I get a red-green image, as expected. But it shortly powers off again with a blinking LED. Also the picture was way out of convergence, but a missing blue PCB connection could probably cause that.

    Having a look at the board, there don't appear to be any bulging capacitors. What other issues with an RPTV would cause this problem?
     
  2. tom66

    Thread Starter Senior Member

    May 9, 2009
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    Ah. Discovered I could enter menu while I thought it was off. I guess with the blue tube disconnected, there is no "blue screen." I turned the blue screen off and it seems to stay on. So I guess the blue TDA6111Q is dead.
     
  3. tom66

    Thread Starter Senior Member

    May 9, 2009
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    Added a TDA6111Q to my order with an electronics supplier - we'll see if this is the only problem.

    What I'm worried about is installing a £3 chip when it might just blow up again. Are there any tests I can do to make sure this won't happen? Are these devices prone to failure? I'm guessing they are as they have a 210V(!!) power rail, and designing high voltage ICs is very difficult, especially in the small size it is. It's stayed on for a long time now without the blue so I don't think the problem is intermittent. Maybe it was originally but it's a pretty permanent failure now.

    Another issue is the video output has a quite bit of noise on it - perhaps a bad cap somewhere is causing interference.
     
  4. Jotto

    Member

    Apr 1, 2011
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    You can test the tube with one of the other neck boards to make sure you tube is good. Do you have a oscope? If so, change the neck board and look at the stair step going to the tube. Change the aquadac clip also. They all basically look the same.

    Measure the voltage being supplied to the neck board. I don't know which tube you have, but if you can supply that I can tell you the approximate voltage you should have. Most neck board problems I have seen are on the neck board and not the main PCB. Sometimes it could be the main board causing the problem.

    There is a cap in the flyback that you should look at. Its usually a low value with a higher then normal voltage. It varies from unit to unit.
     
    Last edited: Jul 27, 2011
  5. tom66

    Thread Starter Senior Member

    May 9, 2009
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    Now I have it staying on and working pretty good (excluding the blue), do you think there is a problem beyond the blue neck board?

    Here is the service manual, it's in 7 parts: http://www.eserviceinfo.com/index.php?what=search2&searchstring=SP42W4HB

    I'll upload the actual pdf later.

    The voltage going to the CRT is 210V. (eek... scared by anything over 50V)

    I will try and probe it and get back with the results.
     
  6. tom66

    Thread Starter Senior Member

    May 9, 2009
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    Hmm tried to measure the 210V bus, couldn't measure it, maybe I wasn't probing it right, although it is shared with all the tubes so I would expect that since red and green work perfectly that the 210V is good.
     
  7. strantor

    AAC Fanatic!

    Oct 3, 2010
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    is the tube/tube assembly oil cooled? my first RCA was. The oil leaked out and the tube overheated and burt everything up/
     
  8. tom66

    Thread Starter Senior Member

    May 9, 2009
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    Think it is, but no oil leaked out. There was a tiny bit of liquid residue on the blue tube though... just a tiny spot. Leaking oil? It looks completely clear. I think the liquid caused the TDA6111Q to fail...
     
  9. strantor

    AAC Fanatic!

    Oct 3, 2010
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    yes clear oil. more likely glycol. I would recommend fixing that before you replace any IC or it will likely happen again. my leaky TV caused most things inside to fry.
    http://forum.allaboutcircuits.com/showthread.php?t=53136

    Info I read on other forums suggested that if it's leaking, it needs to be replaced (as in the whole assembly, with lens). The price for mine was around 250$ each for the assemblies. I think What I read was probably the "shotgun answer" and you could probably get away with not replacing the whole assembly, but I had burnt boards too so I scrapped it,
     
  10. tom66

    Thread Starter Senior Member

    May 9, 2009
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    It's a tiny spot. On the blue tube. I can't just put some sealant around the IC so if it does leak, there is no problem?
     
  11. tom66

    Thread Starter Senior Member

    May 9, 2009
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    Removed the TDA6111Q, and replaced the blue neck board. No more smoke, so it must have been that IC.

    I'm just a little bit worried I'll need to replace the STK convergence ICs as the set is out of convergence, maybe it will be fixable without replacing them but it doesn't look like it. Free stuff always comes with a catch ;).
     
  12. strantor

    AAC Fanatic!

    Oct 3, 2010
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    do you have fuses on your board? My convergence issue was due to a fuse. hard to find because it didn't look like a fuse.
     
  13. tom66

    Thread Starter Senior Member

    May 9, 2009
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    Good point... I will have a look.

    EDIT: Yes, they are called FD101S and FD102S as seen in this diagram.
     
    Last edited: Jul 28, 2011
  14. tom66

    Thread Starter Senior Member

    May 9, 2009
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    Replaced the TDA6111Q. It works, sorta...

    However, the blue channel is still faulty (but at least we get some blue unlike last time.)

    http://www.youtube.com/watch?v=ULjm0AMwdEs

    In fact, I was able to fix the convergence issue. It turned out that running the Perfect Focus routine with blue partially working was enough to focus it pretty good; maybe when blue is properly working it will look even better.
     
    Last edited: Aug 10, 2011
  15. tom66

    Thread Starter Senior Member

    May 9, 2009
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    Okay, this is getting odd. The blue channel TDA6111Q is completely cool to the touch, and yet, the others are warm. But I am getting some video on the blue channel. I left my multimeter somewhere, I suspect I have a cold joint, and I will test it later, when I find the meter.

    Since this thing cost me nothing to get plus a few quid to repair, I was considering donating it to a worthy charity, as it stands it will only sell for £20 if I'm lucky. I checked around town and none could take a 26" CRT that we were getting rid of. Responses ranged from "due to health and safety issues we can't accept over 19 inch TVs", to "we don't accept electricals", to "TV licensing issues forbid us selling TVs." So they probably won't take the 42". Shame, really... it looks to be a nice TV when working.
     
    Last edited: Aug 11, 2011
  16. strantor

    AAC Fanatic!

    Oct 3, 2010
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    Giving up? I'm considering giving up on my TV audio problem (despite the chest thumping in another thread that I would never give up on it). The SMD ICs in concern are so tiny that even if I figured out which one is bad, I would never be able to replace it. The video is just fine & I have a 5.1 surround system so I may put it in the living room and sell the one I'm currently using.

    Sorry I can't help you further with yours
     
  17. tom66

    Thread Starter Senior Member

    May 9, 2009
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    Here's something interesting.

    When I increase the screen control too far, the display starts warbling. I suspect this is because the blue channel is drawing too much current from the power supply and the input capacitor, a 680uF 450V (massive!) is not able to run the set any more between the dips in the AC. During this failure mode, the sound mutes (often after half a second of doing this), but the picture keeps on going (you could try and watch it.) If you adjust it back again, it goes back to normal and within about 5 seconds the sound restores itself. If you leave it warbling for too long, usually 2-3 seconds, it will shut down completely.

    I would therefore check you have a good 5V going into your IC as I suspect my TV has the same IC. (It uses a TDA7269 too.) I see a Micronas chip on the board and I saw references to your chip in my service manual. If the 5V is unstable, the chip doesn't produce noisy output, it just refuses to run.

    I want to get it working before I give it away. I have no need for it as I already got a 42" LCD TV from the dump.
     
  18. tom66

    Thread Starter Senior Member

    May 9, 2009
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    Ack! I'm an idiot. I shorted Screen to GND. Must have smoked something, because it's turning on, but everything is oversaturated, and it turns itself off in a few seconds. I guess it's fit for the trash now! :(
     
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