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Dave2051
Apprentece
10 Posts |
 Posted - Nov 25 2007 : 12:46:58 PM
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I have a Sony Trinitron TV from 1992.
Now, In the last 6 weeks, it has developed a problem: no picture.
When I turn the TV on, I get sound but no picture. Sometimes, a White light flashes at the top and a picture appears. If I then turn the TV off then on again, a picture comes up as it should. If I then turn it off and on, again the picture comes. But every so often, about every 2-3 days, the picture disappears then I have to leave the tv off, turn it back on, and after an hour or so, the light flashes and I get a picture. If some one could help with this without telling me to get a new TV or have it professionaly repaired, it would be very helpful. |
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audioguru
Nobel Prize Winner
Canada
4218 Posts |
Posted - Nov 25 2007 : 4:49:33 PM
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The problem is probably caused by a poor solder joint on the pcb.
The pcb has about 5000 solder joints for you to look at so good luck to find the bad one.
Maybe the high voltage connecor to the picture tube is loose. |
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Dave2051
Apprentece
10 Posts |
Posted - Nov 26 2007 : 12:23:17 PM
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| It's been working perfectly for the last 15 years so I don't think it is a poor soldier joint. The connecter might have become loose but is unlikly because when it is working, and stops working, it FADES out. |
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cyclopsitis
Nobel Prize Winner
Canada
732 Posts |
Posted - Nov 26 2007 : 8:43:36 PM
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I would say it is exactly a bad solder joint. I've done TV, VCR, Stereo repair and over the last ten years 9999 repares our of 10,000 are always related to bad solder joints. That is the first place any repare tech would go to. If it is 15 years old the board has seen humidity, temp changes, lots of vibration and dust. For it to not have a few bad joints would be next to impossible. Pull out the board (after making sure it is NOT storing any chages somtimes 15KV) and just check for bad ones. The way you can tell is it will have a dark ring around the solder pad. I would just go through a re-flow all of them just to be safe and see if it works. Re-flowing is just when you use a hot soldering iron to melt briefly. This usually helps if the solder is old and kinda gloopy you a small bit of solder with this technique and your picture will more then likley come back. However it if it dosn't work I take no responsibilty for it that is why there are repare techs on this planet.
Hope that helps |
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audioguru
Nobel Prize Winner
Canada
4218 Posts |
Posted - Nov 26 2007 : 10:32:39 PM
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| I reflow solder joints with a touch of rosin-core solder. The rosin helps a lot. |
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cyclopsitis
Nobel Prize Winner
Canada
732 Posts |
Posted - Nov 27 2007 : 6:01:21 PM
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| "just a touch". thoes are the words I was looking for yesterday! |
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mrgone
Nobel Prize Winner
USA
1176 Posts |
Posted - Dec 31 2007 : 5:30:38 PM
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| It's the horizontal output. I bet you don't have 75,000 volts comming out of your fly back. You should use high voltage probe to check the annode of the CRT. You won't have it. Try the horizontal output transistor & if not, your flyback is probably fried. You can check the the diode ring & filter caps too. |
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prudayan
New Member
India
1 Posts |
Posted - Jan 09 2008 : 10:33:40 PM
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For the explained you try the following,
1.Open the back cover of the TV and switch on the TV and reduce the speaker volume to cutoff.Then observe if there is any sparking noise from the CRT socket in the CRT board,if it is there try changing the socket.
2.Also check the Screen voltage circuit for any open resistors or dry solder.Definetly the failure is in the EHT section and CRT circuit.Check the filament circuit also.Mostly dry solder will be there. |
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cyclopsitis
Nobel Prize Winner
Canada
732 Posts |
Posted - Jan 10 2008 : 9:02:25 PM
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| For reflowing joints you don't need anything to be on. A working TV could throw you across a room! You probably won't see any arcing a bad solder joint is so fine that an untrained eye would never see it. A good solder joint should be reflective and kind of like a volcano. There shouldn't be too much solder (globs) or too little (look like a collapsed tent). A bad solder joint will have a little circle around the edge or somewhere in there.. it might look like thinner then a piece of hair... The best bet is to just take any joints that are a little tarnished and re-heat all of them applying a tiny bit of extra solder to the ones that need it. |
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Sony TV no picture
