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CRT TV NOT TURNING ON

Thread starter #1
Hi everyone. I'm beginner in electronics repairing and I need help troubleshooting a tv which isn't "fully" turning on.
The board is a cheap chinese universal kit(check attached images for reference) .

When it came to me it was dead...the fuse was blown and V513 was shorted. Since I couldn't find any other faulty components I just replaced the V513 transistor and the fuse, and only for precaution I also replaced the V512 transistor (I read somewhere else that it's a good practice replace the V512 whenever V513 is replaced).

Then, I powered it up through a 60W series bulb, and bulb lit up for about 5 seconds and then it went off and the tv power led came to live and also the that characteristic noise of when the set turning on. I measured the B+ voltages, and they all tested to be good.

so I reconnected the tube and all the "wiring" . Then again I powered it up through the series bulb but this time it took about a minute for the bulb to go off and that noise again. But the screen never came on, the led went off the series bulb came back on and very bright...and yet the noise continues...like the set is on... So i tested the B+ voltages again, primary and secondary, and they all tested fine...till i got to the flyback transformer (fbt). The pin that should be testing +180V is testing 156V insted.

I soldered the FBT ans powered up the set without the fbt, but still the symptoms remain, power led off, series bulb on, noise on...etc., B+ voltages are how they're supposed to be. picture.jpg 20181009_095557.jpg

Can anyone help by explaining me what are the possible causes and/or where to look for the problem.

Thanks in advance.
 

unclejed613

Well-Known Member
#2
156V on a rail marked 180, while it might not be correct, is within the ballpark of "should be working". with everything connected properly, put a sticky note on the face of the CRT with the unsticky edge of the note about 1 cm from the CRT (it doesn't have to be exact, just as long as there's room for movement between that edge of the sticky note and the screen). turn the power on, and watch the sticky note. if after a second or so it either pulls towards the screen, or pushes away from the screen, you have high voltage. if it doesn't move at all, you have no high voltage. you should also see a dim orange glow inside the end of the neck of the CRT. if you don't have any high voltage, then the CRT neck probably won't light up either. if there's a blue or purple glow inside the neck of the CRT, the CRT itself is bad and has air in it. if there's no high voltage, the first thing to check is the transistor mounted on the heat sink that's half way between the flyback and the tuner. that's the horizontal output transistor, and is what drives the flyback. if that transistor is bad, replace it with the same type, do not try to find a substitute. also you notice the small transformer on the other side of the heat sink? there's an electrolytic capacitor right next to it, and that should be replaced. if it's not replaced, it's likely the horizontal output transistor will blow again. never try to measure the collector voltage on the horizontal output transistor, because there are voltage peaks in excess of 1,000V that will instantly fry your multimeter.


EDIT: by the way, the more i look at the picture of the board, the more i think there's a lot of corrosion visible on the tuner and some other areas of the board. has this board got water damage? if so, you're wasting your time trying to get it working again, because once started, the corrosion spreads quickly (like a forest fire, it can "jump").
 
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