Question about RCA P52926 52" Rear Projection Television

2 Answers

Contrast blooming/breathing. R-G-B bias and drive pot values

I own a GE 31GT656 ( CTC169AS2 chassis) manufactured 1/1993.

Problem One: It exhibits geometric "bending" as the contrast level changes in the program material (even with the contrast turned down). I purchased a new flyback transformer in an attempt to correct this. I also wish to replace the "HORIZONTAL DEFLECTION CAPACITOR " while replacing the flyback. I can't locate or identify this part. Do you know the value / voltage rating / part # of this capacitor ?

Problem Two. I wish to replace the TWO "micro" green and red/blue "DRIVE" pots. Also the THREE red, green and blue "BIAS" pots. These are worn out (with "dead spots") and too course in their actions to provide sufficient accuracy in setting the grey scale. Do you know the value of these pots? I hope to substitute a "resistor string" for finer control and accuracy if I know the original values of these micro pots.

Thanks,.....Gerry

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  • vitalvision Mar 06, 2009

    The picture shown was taken with a cell phone after the flyback was replaced . What's displayed is a Colorfacts test pattern called " adjust contrast " fed from my computer into the S-video input of the TV. Notice the deflection of the picture. Certain portions are "wavy" (especially at the top).The less white level present,the less geometric bending. When viewing regular program material containing little or no white level, there is no bending at all.(The two horizontal "white bars" are artifacts of the cell phone used to take the picture. They are not visible when viewing the actual set in real time).

    It's also a "warm up" problem. Turned off overnight, there is no color for about 5 minutes when turn on again.During "warm up", there is no geometric "bending". After 5 minutes, color intermittently disappears/reappear as I change channels. When warm up is completed (15-30 minutes), color is fully restored. But so is the "breathing" as white level changes from scene to scene.



    With the new flyback, using the Nokia "high voltage" alternating full black/ full white test pattern as a signal source, the "breathing" or "bending" issue is vastly improved over the old flyback. But it is not completely eliminated, even after full warm up. It's been suggested that I replace Horizontal Output Transistor Q 4401 /RCA part # 200167 (attached to the heat sink). I'm not sure replacing this part will solve the problem, but it makes intuitive sense to do so.



    Using the "Sound and Vision Home Theater Tune Up" DVD and displaying the "coarse focus" pattern from the "advanced test pattern" menu, the multiple "cross hairs" placed symetrically at various points on the screen are VERY distorted. Thanks for all your suggestions. It seems that there are a lot of capacitors to replace. The downloaded service manual is helpful but a pain to "read" on a computer. Here's the cell phone picture of "my problem".


  • vitalvision Mar 06, 2009

    The picture shown was taken with a cell phone after the flyback was replaced . What's displayed is a Colorfacts test pattern called " adjust contrast " fed from my computer into the S-video input of the TV. Notice the deflection of the picture. Certain portions are "wavy" (especially at the top).The less white level present,the less geometric bending. When viewing regular program material containing little or no white level, there is no bending at all.(The two horizontal "white bars" are artifacts of the cell phone used to take the picture. They are not visible when viewing the actual set in real time).

    It's also a "warm up" problem. Turned off overnight, there is no color for about 5 minutes when turn on again.During "warm up", there is no geometric "bending". After 5 minutes, color intermittently disappears/reappear as I change channels. When warm up is completed (15-30 minutes), color is fully restored. But so is the "breathing" as white level changes from scene to scene.



    With the new flyback, using the Nokia "high voltage" alternating full black/ full white test pattern as a signal source, the "breathing" or "bending" issue is vastly improved over the old flyback. But it is not completely eliminated, even after full warm up. It's been suggested that I replace Horizontal Output Transistor Q 4401 /RCA part # 200167 (attached to the heat sink). I'm not sure replacing this part will solve the problem, but it makes intuitive sense to do so.



    Using the "Sound and Vision Home Theater Tune Up" DVD and displaying the "coarse focus" pattern from the "advanced test pattern" menu, the multiple "cross hairs" placed symetrically at various points on the screen are VERY distorted. Thanks for all your suggestions. It seems that there are a lot of capacitors to replace. The downloaded service manual is helpful but a pain to "read" on a computer. Here's the cell phone picture of "my problem".


  • vitalvision Mar 11, 2009

    Regarding download schematic for GE 31GT656 , chassis # CTC169AS2. It has discrepencies (errors ?) I can't figure out.



    According to service manual version 13 (page 12-68 &12-69) three BIAS & one G DRIVE are identical (part # 190533). The R/B DRIVE is part # 190531. And all three "bias" pots ALSO decribed as " DRIVE" ).

    Schematic (pg 9-10) contradicts this: says 3 bias pots = 4500 ohms, drive pots = 100 ohms.Schematic cordinates for these pots as follows.

    R 2926 (R/B DRIVE) : 89C - Part # 190531
    R 2928 ( G DRIVE) : 89E - Part # 190533
    R 2913 ( R bias) : 92C - Part # 190533
    R 2921 (G bias) : 92E - Part # 190533
    R 2917 (B bias) : 92F - part # 190533



    Who knows the correct part # and / or values for these 5 adjustment pots ?



    And I haven't even solved the contrast "breathing" yet. The snapshot picture shows "slanting" to the left. This "bending" is consistent with all normal programs (not just test patterns).

  • Henry McKelvey
    Henry McKelvey May 11, 2010

    Hello vitalvision,



    Are you in need of a schematic? I ask this question because you obvisouly know what you are doing, but you can not find the component values on the board, this is a sign that what you are asking for are the values of parts, and not how to go about doing the actual repair job.

    Here two sites I use to get schematics:



    http://www.manualsparadise.com



    http://www.servicemanuals.net



    the cost of the schematic is aroung 16.99 for a downloadable version.



    I hope this helps



    Shuttle83



    http://www.electron-age-technologies-llc...

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The three bias pots are 4500 ohms part # 190533 each are the same. The two drive pots are 100 ohms part # 190531 each are the same . On your other problems your headline states contrast blooming / breathing , this could be a sign of a weak picture tube or the screen control could be set too low . Now as far as the bending as the contrast changes , i would need more info . for example if the screen changes from a dark screen to a bright screen and the sides pull in suspect C4401 , C4402 or C4403 . Sometimes these tend to bulge at the sides . Now if C4402 is your problem also replace CR4402 . These would be the capictors in your horizontal section that give this chassis the most problems . Also a capictor in the power supply also is commonly bad in these sets . C4102 which is a 2.2mfd @ 100v . Now if your picture is not stable as far as the picture is full but everything slants alittle suspect the PIP module . Sometimes there are capacitors that are weak and won't let the picture stay stable . Hope i haven't confused you much but without seeing the picture its kind of hard to tell for sure . If you need any more info or part #'s let me know . TeamTech P.S. good luck in your repairs

Posted on Mar 06, 2009

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If the picture is only bending in on the sides the problem is in the pincushion circuit. If it is the entire picture there is a voltage regulation problem either in the power supply circuit or the power supply off the flyback transformer which is usually a diode and capacitor combination. If you want to go with the odds, replace CR4118 with part number 164590. You may want to put the original flyback in as there are many problems with aftermarkets and even if it is an RCA part it is still aftermatket. As far as the bias pots a little cleaning spray usually does the trick. I wouldn't worry about trying to get a perfect grey scale out of a 16 year old tube, the original pots are plenty accurate.

Posted on Mar 06, 2009

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