"perfect focus" problem Samsung HCN4727W rear projection

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"perfect focus" problem Samsung HCN4727W rear projection

I had the usual Samsung convergence problems on a Samsung HCN4727W5S/XAA rear projection TV.  The STKs and resistors were bad.  I replaced the convergence board and the convergence issues were almost completely gone.  The user accessible red and blue convergence and perfect focus all worked fine.  The only problem was a very small 1/16” red convergence line on a small part of the user convergence screen.


I downloaded the service manual; then was able to enter the service menu and service convergence modes and adjust the convergence slightly to eliminate the slight red mis-convergence. 


I do not have a screen jig, but used two pieces of string taped to the TV to mark both the edge sensors and the center of the screen.  The convergence grid is square with no distortions and the center lines line up precisely with the sensors and screen center.


I was careful to save the RBG adjustments during the service menu convergence procedure and did the “Perfect Focus” from the service menu at the end of the convergence procedure. 


The “Perfect Focus” within the service menu does not seem to finish and save the settings.  It goes through 100% a few times, the RBG lines pass through the plane of the sensors, the numbers adjust, but the process ends with a white screen instead of reverting back to the convergence grid as the service manual seems to say it should.  I exit the convergence procedure with the “s-mode” key as the service manual instructs.


When the TV is back on in the normal user mode, the picture looks good but the “Perfect Focus” function no longer works.  I just get the “no sensor data” error message. I assume this is due to the “Perfect Focus” function in the service mode not finishing and saving the data.


The “Perfect Focus” did work after replacing the board before I started fine tuning the convergence in the service mode.


Any ideas is to what I am doing wrong?




i have never worked on

i have never worked on Samsung, but Hitachi can have a similar problem, and in the Hitachi if you tweak the vertical width or the horizontal width a little it will usually fix the problem. there has to be enough over scan to hit the sensors, turn the tv on and see if the sensors are getting hit with video. Also, you may need to tweak the centering vertical and horizontal. The blocks have to hit correctly on the sensors, just hitting the sensors may not be enough. They may have to hit at a certain point before a successful perfect focus will work, Although i don't take too much stock in the autofocus on any brand. the correction is very narrow, and a manual convergence does a much better job. If you don't get it running again i wouldn’t consider it a big loss. i always felt it was more gimmicky than helpful.

While you may think you had

While you may think you had the geometry and convergence correct when you finished, the fact that the self focus didn't successfully save nor work now indicates you didn't.  One of your sensors isn't recieving an adequate amount of light from the crt to work correctly.  You can either redo the entire convergence or live with it.

How do you enter the service

How do you enter the service mode on this tv? Please Let me know!

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I am having the exact same

I am having the exact same issue. I am getting a


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