Question about Mitsubishi VS-50707 50" Rear Projection Television

2 Answers

Mitsubishi Rear Projection makes funny shapes on Green and Blue

I have a Mitsubishi VS-50707 with a very strange pattern on-screen.

Here is a picture:

I have opened up the back and tried tapping the resistors andcapacitors in the convergence chips (I think) with a wooden shim, Itried flexing the board a little to see if there was a cold solder, butno change.

I went into the advanced menu and was able to move the blue and red around.

Is there any service menu I can activate to adjust them? Or do I need to troubleshoot one of the convergence chips (capacitors, resistors, fuses)?

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  • b4ui8fastfoo May 20, 2009

    What type of package are they in? Where would I be likely to find them on the PCB?

    Green PCB:

    Brown PCB:

  • b4ui8fastfoo May 20, 2009

    The Service manual indicates that the amp IC's are under this shield. Should I try to pop the lid off, or is desoldering from the underside the better choice? There is a shield underneath suspended from the pins of the box on top.

    I looked at the underside and found that the Convergence IC's had been replaced, and had some sketchy solder joints. I am going to try and clean them up.

  • b4ui8fastfoo May 20, 2009

    I popped the cover off of the shield, I cooled the amps with an upside-down canned air, they had frost on them and were cold to the touch.

    No change to the blue or green image.

    I did a quick re-heat of the solder on all of the convergence IC pins, removing some of the excess, that didn't have any effect either.

  • b4ui8fastfoo May 21, 2009

    This is the circuit from the service manual, assuming I had an oscilloscope, what would I be looking for? (if there is a guide on scoping I could sure use it, I have used DSO scopes in the automotive field, so I would likely clip the ground to the shield, and then check to see if pin 7 and 8 on IC802 were making a similar signal, if not then I would see if they were receiving a similar signal on pins 2 and 13).

    Is it standard to have one amp circuit fail in a package like the IC802/3? Because it would appear that is what happened to these two chips, as they are shared with RH and RV and those seem to be working fine.

    I have checked the resistance from the CONV to the D/A, D/A to the AMP, and from the AMP to the Convergence IC for RH, BH and GH. The circuits appear to be fine.

  • b4ui8fastfoo May 22, 2009

    I took these connectors and swapped them, Red for Green and Red for Blue, there was no change in the picture!

    I scoped pins 7, 8 on IC802 and pin 8 on IC803, Pin 8 (RH) on IC802 had a nice high waveform, whereas the other two pins had poor looking waveforms, not very high.

    When I scoped the output of the circled wires above Red H+ had a waveform similar to the AMP pin, and Blue and Green + looked poor like their AMP pin's waveform.

    Red H- had a tight waveform, as did Green H-, but Blue H- looked poor.

    I am going to check the resistance of the yoke coils now, because there was no difference when swapping blue or green for red.

  • b4ui8fastfoo May 22, 2009

    To confirm, I swapped BH +/- for RV +/-, when I set the convergence in the menu the red moved up and down while the blue moved left to right.

    When I chose to adjust the blue the red would move left to right.

    Does this mean that there is a problem with the yoke? There is a PCB on the yoke with heavy wires coming from the High voltage section, Red, Blue Yellow and Brown, these travel to each yoke.

    Yellow and brown appear to be in a series connection (vertical??) and Red/Blue have two wires apiece on the two yokes nearest the High-voltage PCB, with one blue and one red on the last yoke.

    This is the schematic for that section:

    It is starting to look like the convergance IC is working the deflection coils without help from the main deflection circuit, the IC451 (chip LA7845N), if it only has enough power to run the first yoke (the red one), then would it cause this kind of problem?

    Could the fault be in the first yoke PCB that sends the deflection current in a parrallel circuit?

  • b4ui8fastfoo May 22, 2009


    I poked the first yoke PCB with a stick, and guess what? A spark, some ozone and all the colors!!

    (I had just sprayed the two transistors on the power PCB with an upside-down can of air)

    Unfortunately I reset the factory convergence settings in the service menu, and I don't have the original remote, so I will need to program my remote with an Audio button before I can get it properly aligned.

    I guess it is time to swap back all the convergence wires and solder the RF shield back on the bottom.



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Your Green and Blue horizontal video amplifiers have collapsed: try using a freon cold spray on these chips as this occurs when the heatsink grease dries up on the HVA chips and, causes an overheat condition; if you have an oscilloscope monitor the vert drive as well.

Posted on May 20, 2009

  • 4 more comments 
  • Jim Goldsmith
    Jim Goldsmith May 20, 2009

    yes unsolder the cover the shield is grounded be sure to resolder the shield test with freon component cooler from radioshack

  • Jim Goldsmith
    Jim Goldsmith May 20, 2009

    Unless you have an oscilloscope you will need to schedule a service call; sorry I couldn't help you

  • Jim Goldsmith
    Jim Goldsmith May 21, 2009

    That is correct; check for loss of amplitude across the signal; as you understand oscilloscopes think of the circuit board as an ignition module 12 volts goes in at 40 amps 30 kv comes out to fire the sparkplugs You would: start at one end: 12v next 48v next 96v? but; only 52v ! ? there's a problem... I will review your schematic and, let you know what I find

  • Jim Goldsmith
    Jim Goldsmith May 21, 2009

    Here is how to check with a meter:

    you can compare the "Good" voltages on your circuit board that I have reviewed to the "bad" green and, blue voltages: think of the circuitboard as a room "measure the front door then go to the back door and, measure it; check the input then the output of the board write down the values then pull off the horizontal picturetube yoke wires and, carefully measure these you should see that the red voltages are high the blue and, green low then: to be visually sure remove the horizontal hoke wires from the red yoke and, the blue or, green and switch them now red should be "bad" and the other screen "good" The screen is "painted by moving a beam from top to bottom with the yoke electromagnets So because you do not have a vertical line in the middle of the screen (horizontal collapse) your vertical hokes are working a little bit

  • Jim Goldsmith
    Jim Goldsmith May 22, 2009

    Very good! this may sound redundant but: are you sure you swapped the horizontal yoke coil wires? and, not the vertical ones?.. I'm starting to suspect shorted horizontal yoke coils please post the coil measurements

  • Jim Goldsmith
    Jim Goldsmith May 22, 2009

    I think you got it! as you see the sawtooth wave form of the yoke magnets in the yoke "paints" the video lines from the left top of the screen to the bottom right then shuts off to go back up to the top left again; it does this 2 times every 60th of a second (two passes in one second) 60hertz let me know if you need further help


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My tv just keeps rolling please help!!!!!!!!!probono

Posted on Jun 21, 2009


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