Question about Toshiba 57HX81 57" Rear Projection Television

1 Answer

My Toshiba 57HX81 works ok for a few minutes before going out with the flashing red power LED. The diagnostic menu shows "Power :002" for the operation number of the protection circuit. All related tech manuals I've seen indicate that should be 000. Does anyone know what this is pointing to? I'd love to reduce my diagnostic efforts here! Thanks.

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  • 5 more comments 
  • mfoegelle Sep 29, 2010

    Thanks, I'd already seen that's a common problem and checked the fuses. None test as blown. The fact that the TV does power on and work properly and then shuts down after a period of time would seem to point to something a little less straightforward. It may well be the convergence chips about to go, or just as likely a cold solder joint in the area. Since the TV has a diagnostic code it's giving me, I was really hoping to find out the meaning of the code as opposed to just assuming it's due to the most common problem that's already publicly posted. Under the circumstances I'm not quite ready to just start desoldering convergence chips to do the diagnosis! At a minimum, guidance on the "easiest"/least intrusive way of pulling the power and convergence boards (I'd rather not pull the whole light box as shown in the service manual) would be appreciated.



    Thanks,



    M

  • mfoegelle Sep 29, 2010

    Thanks for the tip on the chassis. Much easier than I'd feared. I've double checked all fuses and no problems there. I'm assuming the resistors you're referring to are the convergence coil return limiters R7711, 16, 21, 26, 31, and 36 (1.8 ohms) all of which read about 2 ohms on my DMM. So, still no evidence of ancillary damage around these parts, but barring any other suggestions I guess it's time to heat up the soldering iron and **** some solder!



    Thanks,



    M

  • mfoegelle Sep 30, 2010

    Well, no joy. After desoldering and removing both ICs, the unit now goes straight to the flashing LED on plug-in/power up.

  • mfoegelle Sep 30, 2010

    Did so immediately after trying the unit. No such luck!

  • mfoegelle Sep 30, 2010

    No, but lifting up a large flexible PCB assembly that has intermittent contact would easily result in a permanently broken contact. I've already run continuity checks on the pads for the chips to ensure there were no bridges, etc.

    Trying to trace connectivity everywhere isn't terribly practical. To start testing under power I need to be able to leave the PCB in the upright position to allow probing the bottom of the board. There's one connector (P111 I believe but would have to double-check) for a cable heading towards the front through a ferrite core that I'd have to leave off. Not sure what problems leaving things open circuited like that might cause...

    Any recommended test points other than at the fuses? Note that I also have an oscilloscope, etc. at hand for more elaborate diagnostics.

    Thanks,

    M

  • mfoegelle Oct 01, 2010

    Unfortunately that's easier said than done as it will require disassembling the front panel. I may not get to that before I have to head out of town for a couple of weeks!

    M

  • mfoegelle Oct 01, 2010

    Ok, pulled everything and checked the voltages on all fuses and on the caps just past the rectifiers for the /- 32V supply for the convergence ICs. Everything checks out to within about a volt. A couple of points read a bit high, but that's most likely due to failure to stabilize in the few seconds it's on. The /- 32V supply is more like 38/-34, but that's because there's no load with the convergence chips removed. The caps are holding their charge long after the set powers off, so that's not the problem either. I checked that supply all the way to the convergence chips and it reads the same there, so again not the problem...

    In summary:
    F470: 120V
    F850: 17V
    F851: -17V
    F852->C852: 38V (no load)
    F853->C854: -34V (no load)
    F860: 120V
    F889: 33.8V
    F890: 11.4V
    F891: 8V

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  • Toshiba Master
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In this model it should be short protection--I suspect the convergence chips--each is protected with a pico fuse--two identical voltage sources--one is a positive and the other a negative voltage--if either blown--locate the chips and unsolder both--with fuse replaced and chips not soldered in--see if set comes on--if it does convergence will be out the window but you will know one of the chips is shorted--there are also number of protect resistors around them--usually 1.2 or 1.5 ohm--they will look perfect but if open.....

Let me know what you find.

SD TECH

Posted on Sep 28, 2010

  • 3 more comments 
  • SD Tech
    SD Tech Sep 29, 2010

    Trouble shooting always involves trying to rule out what may or may not be the problem. You will not wave a magic wand and know what the problem is---if you tested the correct fuses and they are good it still could be the chips---You do not have to remove boards etc, it is quite common to undo some cables and leads and lift the entire chassis up so the bottom in facing the back of the set--10 minute task.

    Ten minutes more to remove solder from the chips and KNOW.

    The possible bad connections is real--some of these had jumpers in the area of the chips that break loose---No one can tell what the problem is without trying to confirm or eliminate certain things.

    If not the chips, it involves monitoring major voltage sources out of the power supply--which goes off or down first? Not easy, which is a good reason to eliminate the convergence chips first--if they have never been replaced they are the place to start.

    With both chips unsoldered the set will still come on and look bad---but does it stay on for say twenty minutes this way?

    I have been fixing sets for over 30 years---you must rule out the clear possible reasons first--it is just as valuable to know what is not the problem as it is to know if it is the problem.

    Undo the chips--if the problem is in the area or the supply voltages you will know if it is or is not the problem.

    If you do not do this you are using a dartboard---I do not suggest just replacing them but seeing if they are the problem.

    SD TECH

  • SD Tech
    SD Tech Sep 29, 2010

    For some reason my answer did not appear and I did not get a email.

    You cannot wave a magic wand here. Troubleshooting involves ruling things out.

    The board does not have to be removed--with some of the plugs that are bundled up loose there is plenty of room to get the entire chassis up so the bottom of the boards face the back of the set. Undo the solder on both chips, ten minute job.

    Even if the fuses are good, one of the chips may be causing this--no need to replace to find out--there are also some metal jumpers in that area of board that break loose from board.

    Rule chips out first and then you will know if they are or are not the problem.

    SD TECH

  • SD Tech
    SD Tech Sep 30, 2010

    Double check the fuses associated with the chips to see if gone bad.

    Let me know what you find.

    SD TECH

  • SD Tech
    SD Tech Sep 30, 2010

    Double check what you did when you undsoldered chips--no shorts---removing solder should not cause this problem--solder chips back if you have to and see if problem as before.

    Another option is to test voltages on the two fuses--one should be positive and the other negative voltage.


    SD TECH

  • SD Tech
    SD Tech Sep 30, 2010

    free the cable, you cannot leave a plug undone.

    I am going off the internet now and will return after noon tomorrow Pacific time.

    SD TECH

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