Question about Samsung HCL4715W 47" Rear Projection Television

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Convergence problem After 5 years of excellent peformance, the convergence problem began to show up, first as an intermitent loss of convergence over a period of about six months. Finally, yesterday the blue and green curved into a horizontal arc (pin cushion?)ie top and bottom half curved in towards the center of the screen. Blue convergence adjustment now has no effect. Red seems ok as it is still linear and still adjustable. Video and sound is OK. Need advice on possible areas of concern particularly on a most likely chip that governs the green and blue crt convergence controls. The symptoms of intermitent failure to total failure of the convergence adjustment seems to indicate a possible gradual degradation of a certain chip rather than an intermitent connection or a bad solder joint. Any advice from anyone with a similar experience?

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  • Fredlee Aug 28, 2007

    Today I replaced the two STKs. Before I resoldered the new chips (with it's heat sink and of course with new heat senk compound from Radio Shack), I made some in-circuit resistance check of the relatively large high wattage resistors associated with the STKs and they were all comparatively identical. If one of them had open circuited, it would have shown a different resistance reading (due to other back circuits). Regretfully, after re-installing the new STKs and subsequently powering up the set, the convergence anomaly were exactly the same observed before the STK replacements. So, it appears there is something else causing the blue/green convergence problem other than the two STK392-040. Any other suggestions would be highly appreciated.. thanks.

  • Fredlee Aug 28, 2007

    Thanks, Techman
    Ye, I do have a detailed service "manual" downloaded from the internet for a price. Needless to say, the manual is mind boggling, too many details. Fortunately, the problem I believe is purely on the display side and not the video/audio signals. It has been quite a long time since I messed around with the old analog TVs of the seventies. I have a multimeter (analog Sanwa 20kOhm/volt DC). I like analog multesters as they are great for measuring approx charge/discharge of capacitors by the amount of needle deflection in the Ohms position. I will follow yur suggestion first thing in the morning and check out the +/- 30V and the fusible resistors (why did'nt I think of that?). I don't feel bad about replacing parts based on initially reasonable assumptions as in most cases it works without having to probe too deep into the set and make a lot of measurements to come to that conclusion. I should have known a cold STK is definitely a short inside it and could have blown a fuse as an overcurrent protection feature. Many thanks for your suggestion, I'll now have to get down to more serious troubleshooting and hopefully, replacement of a blown fusible link would be the answer. Will let you know the outcome soon. My email address is fredleeway@gmail.com

  • Fredlee Aug 29, 2007

    Switching power supply bd circuit protectors are OK although thaey have different numbers than what you mentioned.
    I found FD1028 fuse(3.5amp 125V )right undereath the STK heat sink to be open-circuited. I do not have a replacement fuse on hand so I used a temporary jumper (very thin single strand copper wire) across the blown pico fuse. Upon switching on the set, the green and red came out perfectly OK and the picture came out linear. However, blue was way off to the right hand side of the sceen. Tried to bring the blue to converge on to the green and red crosshairs via the remote controller in the convergence aligment mode although it took quite some time to bring it together. It got close to about one inch from the crosshairs and no further (I wonder if the continued usuage of the convergence alignment controls does overlaod the STKs ?? I noticed some severe linearity problem during attempt to bring the blue back in line. Then after about 10-15 minutes into the alignment attempt, the screen started to flicker and then pfft! went blank. Tried to switch off the set immediately thereafter but there was no response, so I quickly pulled the plug off the mains supply, just in case something may be burning inside. Found both STK heatsinks were exptemely hot to the touch ( don't know if the untouchable hotness is the normal operating temp. of the STKs. After allowing it to cool down for about 20 minutes, I powered up the set again, switched it on by remote control and found the picture curved in this time only downwards on the green and blue. The red retained its perfect linearity and adjustablility. Blue has lost its adj capability again. FD 1028 has blown again (perhaps the temp fuse may be too thin or maybe the inferior STK may have blown the fuse. I have already placed an order for new 3.5amp pico fuses from Bluestar-online and 2 STKs from mcmelectronics.com. I will await the arrival of these two components before proceeding further. You are right about the cheap STKs. They could well be deficient in some ways that may have caused the blue to go way off the mark. Did I overlooked a certain procedure to restore an "initial convergence setting immediately upon replacement of the STKs? It seems to me that the blue adj ran into some kind of "saturation" that may have resulted in excessive current draw resultig in excessive heat generated by the STKs. I am only speculating, perhaps I need some enlightenment?

  • Fredlee Aug 29, 2007

    Yes, I never missed out on the heat sink compound. I did use new heat sink compound bought from Radio Shack. I am fully aware of heat dissipation issues on heavy duty semiconductors. In fact I did noticed the original heat sink compound was very dry and brittle when the STKs were first removed. That I presumed may have been the original cause of the STK failure due to poor thermal conduction to the heat sink. I had put in a generous amount of the compound such that it oozes out as I tighten the two STK mounting screws on the heat sink. Thanks for the reminder anyway.
    I did not have the chance to measure the +/- 30Vdc on both boards as I switched on the set and immediately noticed the vast improvement on the screen (except for the blue). I see your point in emphasizing on the importance of the bipolar as it may have effect on the adj span on the blue convergence. I will be checking on that this time around after replaceing new STKs and the blown FD1028 in-line fuse. I had checked all other fuses on all boards were OK
    and all fusible resistors measured up to their stated color-coded values. Hope this time the right fuse and the verification of the +/-30vdc presence on both boards will see the satisfactory conclusion of this interesting troubleshooting endeavour.
    Like I said, ithas been years since I messed with Radio & TV servicing. It is all slowly coming back to me now.

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The convergence board is bad in this set. Samsung no longer has this board in stock. You will have to take the board out and rebuild it by replacing both of the STK convergence amp IC's These IC's are soldered to the printed circuit board. They will be standing up against a metal plate, called a heat sink. They are black in color and are about 2" by 3" . They have white lettering on them that start with STK and the some numbers. You get those numbers and go to mcmelectronics.com, enter the exact number of the IC and order two of them. Before you install the new IC's you will need to apply some heat sink compound onm the back of the new IC's. This heat sink compound is avaialable thruogh radio shack. Good Luck

Posted on Aug 23, 2007

  • Larry  Dillon
    Larry Dillon Aug 28, 2007

    OK, do you have a multimeter and a service manual for this set? Sometimes, when these IC's blow out, it will take out the circuit protectors on the convergence board or possibly blow out the fusable resistors or circuit protectors in the power supply. You will first need to check out the plug number CN803 on the convergence board. You should be able to see where the pin # one is, as it will be marked on the board. Check, with the set on, pin number 12, there should be 30 volts or about that on this pin. Next, check pin # 9, this should have about a negative 30 volts on there. If any of these are missing, I will explain this in a second. If these voltages are confirmed for sure to be going to this board. Check for the fusiblae resistor RF801s on the convergence board. This should measure like a fuse and be nor resistance, a total short. Now if any of the voltages are not there on the power plug on the convergence board, go to the switching power supply board and make sure the in line circuit protectors, #s FD855 and FD802 are good. they should check just like fuses. Do not feel bad and think you replaced parts that did not need replacing. This happens almost all the time when these IC''s go bad, and fuses or resistors are there to stop the rest of the set from shorting out or blowing up when these IC's do go out. Good Luck. Oh by the way, if you can follow a service manual, I happen to have one, as I have had to repair a set just like yours, with the same problem in the past a few times already. just leave an e-mail address if you want to save your self at least 25 bucks or so.

  • Larry  Dillon
    Larry Dillon Aug 29, 2007

    You need to make sure the plus and the minus 30 volt supply is on BOTH IC's. The alignment should not be that off when replacing the IC's unless you messed with these adjustments before you replaced the IC's. Yes, the heat sink will get very hot. Before you replaced the IC's into the printed circuit board. Did you put a good coating of heat sink compound onto the back of the new IC's. This is a step a lot of peeps forget and this will cause the IC's to over heat and to burn out. I did mention this in the very first post.

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