Mulja tv repair portal
Equipment Repairs => CRT TV forum => Topic started by: AshayinFLA on May 24, 2009,03:12:30
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I was given a sony kp-57hw40 that supposedly had a bad flyback, as per the previous owner's research on the # of flashes of the status light. Since it was in storage for >1 yr, I felt comfortable changing out the flyback with a brand new one I was able to obtain. When I did the job and turned it on, there were a few blue flashes on the screen and then it shut down and went into protect (and status flashed 8 times). I then hit the pwr button and it did the same thing, but flashed 6 times instead.
After lots of research, I opened up the front to get to the screen plate voltage level controls and tried to adjust them. What I found is that when I turn the blue knob down (to the left) it stays on longer, but the green trace lines appear, then I would turn the green down to compensate. If I turn UP the blue knob, it NEVER makes blue trace lines, but the whole screen will eventually turn blue and then go to shut down if I keep turning up. When it hits protect, I can achieve a flashing status light of 5, 6, or 8 flashes depending on the position of the voltage knobs. Whatever I do with the blue (even when all the way down) there's still blue flashes every now and then, but the higher I bring up the blue voltage, the more flashes there is on the screen. If its almost all the way down the screen will stay on (minimal flashes) and not go into protect, for at least 5 or 10 minutes. I never put signal into the box and don't have test patterns (or a remote to enter test mode yet, but my sony remote for my sony hd tube set might work? I haven't tried yet) but I looked at the menu screens, snow, and auto-convergence pattern as viewing signals (I also turned down the picture and put the brightness ~50% as recommended in the manual, before I set g2 levels). Even with the blue g2 voltage all the way down, it might hit protect when switching input sources, as it makes long bright blue flashes when switching, sometimes. The blue picture also seems to be out of focus, or has a halo around it no matter what I do. I tried adjusting the focus knob, but it only gets worse in either direction so its already set as good as it could be. I am expecting that I will need to change the coolant because of this? (confirm, please?) I am wondering if old coolant can be causing all my problems (I doubt it), or if its other electronic components to replace (resistors or convergence amp or something), or if the flashing is being caused by a crt tube going bad (I hope not!). I have not yet tested voltage on different boards / tp's, and am a little confused about how exactly to wire a g2 jig, as recommended in the manual (I already d/l the manual). One last note, is that the auto-convergence is out of line, as it does go through the motions of trying to adjust, but then after its done (it does it's thing twice) it reverts to an out-of-convergence position, rather than getting the picture lined up right; but when it's trying to adjust, it looks like it gets pretty close even though it doesn't stay close when it's done. This tv was given as a project/gift and I would love to get it up and running, but I don't have the money or want to really spend on it if it gets expensive. My backround is audio gear (mostly pro audio gear) and I have experience with a soldering iron and board level repairs (with minimal component-level troubleshooting on my part, except for cold solder joints and burnt parts or bad caps) but I can read a schematic and follow/trace a circuit and use a multimeter to test things. I'm a little weary of the hv from the flyback now that its been energized, but not afraid to de-energize it to do more repairs. Any help would be appreciated! Thank you.
edit: The number of status flashes I am working from memory, but it might not be the correct #'s. I know the status codes were for voltage or current overloads, a particular bad part# (5 flashes), or white balance off.
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It may be possible the video driver chip is bad. I replaced one on mine and get the set working again.
This is the small circuit board attached to the picture tube. There was a small resistor that had blown, as well as one on the main board near the connector that connects the driver board to the main board.
I replaced the resistors and driver IC. Of course, it could be the blue crt is is shot.
Hope this is helpful.
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It sounds like the blue tube may be faulty, if adjusting the focus in both directions makes it worse. If that was all that was wrong (before you put everything out of adjustment !) perhaps if you unplug the blue tube's neck board, you may be able to get the set running with just red and green and see if it is stable and otherwise fully functional. Make sure that the neck board can't short to anything while it is hanging free. If that tube turns out to be faulty, it may be possible to have it rejuvenated. This would normally be done in the set by the technician. The cable from the instrument plugs on the back of the tube where you removed the neck board and provides high current pulses which rejuvenate the tube. Don't expect to get good convergence while things are faulty or unstable. If the cables are long enough it may be possible to swap the neck boards between tubes to decide whether you have a tube problem. Don't be too anxious to physically remove a tube, you will be making a lot of work for yourself setting up afterwards. I don't know the set, but am a qualified TV tech. I have worked on only a half dozen 5" tube type projectors, though have lots of experience with shadow mask picture tube sets. Don't kill yourself on the high voltage applied to the side of the tube. There should be no need to disturb it, and no need to swap the deflection yokes or yoke connections for the test as the three yokes are all fed with about the same signals, disregarding minor geometry correction differences. .....One step at a time.
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Do the 3 guns get driven exactly the same (so you could switch driver boards between them and it should not burn anything out)? I guess I should be able to swap the boards and see which part is faulty if thats the case. I am pretty sure that if I was to remove the blue tube from the circuit that if it is not flashing it will not overdraw the power supply causing the protection. If I was to simply unplug the blue circuit board from the tube, will it do any more damage (I know running some amplifier circuits without a load is damaging to the transistors/components) if I ran it that way for test, or will it cause the protection to enable as it senses a failure? As for the focus, I could easily focus the other colors with any solid lines on the screen (like text or a cross hatch; they were already as good as they could get) and the blue was already as good as it could get too, but the "halo" around it would not disappear. I read about the coolant going bad in the tubes and it causes that. IS that a possibility or a probability or not likely? I also read that the "proper" way to change the coolant would involve removing the tube and cleaning every part of it as part of the process.
Finally, I know the flyback feeds a distributor, which then feeds all 3 tubes (so they do get the same signal). IS there any risk of shock if the tv is unplugged, if I don't mess with the hv wiring (for instance if I only unplug the tubes from the driver circuit but not the hv wire then can hv arc to the driver pins/circuit?) or is the high voltage contained inside the tube and hv wiring and cannot leak out of anything else? I am guessing that to empty the hv voltage I would need to open the last cap on the distributor (which normally has no wire in it) and stick a wire in that is connected to a gnd lug of my house? Is that the best way or is there another better way? Is there any safety measures to take while doing that (certain type of wire, or wire with certain amount of shielding) or should I gnd to the set's gnd/shield and not to a lug on my house (to protect my home from lightning)? Stand on wood??? I guess I should know this stuff before thinking about messing with it, but last time it was not plugged in for a year so I wasn't worried.