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horizontal output transistor short

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Last response: in Other Consumer Electronics
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June 12, 2013 6:15:31 AM


LG 29" CRT TV (RT-29FC85VW).

Again and again 2SD2689 gets short.

After replacement, raster appears for one minute with horizontal shrink and stretch ( less and full ) about an inch on left and right side .

Checked the damper diode. It's ok.

(Sorry guys. This is a repeat of my previous thread put on two days back (10th June). I have put this question in another place " Ask the community" guessing some experts will reply. But never expected it will be repeated here. Now I don't know how to delete this second post)

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June 19, 2013 11:32:30 PM

At last, myself have fixed the problem.

Since the replaced transistor blows within a minute, I could not diagnose with voltage measurements. I had to check the components, associated with deflection circuit, in cold condition. All capacitors, resistors and diodes are found in good condition.

When checking the Line driver transformer's (T401) secondary winding, it showed 2 ohms to 33 ohms variably. But it should be @ 2ohms ( constantly ) and not upto 33 ohms. There is a 33 ohms resistor across the winding in the circuit. So the problem is one of the leads of the Line driver is having intermittent contact with the Circuit board.

I have checked with magnifying glass and found one pin of T401 is in loose contact with the PCB. Already at this particular point of the PCB, the original amount of lead ( soldered ) is very low. Hence when I was removing the nearby Horiz. Output Transistor, this particular solder point has developed crack, causing intermittent connection and failure of Horiz. Output Transistor.

After applying adequate lead at that point, and freshly replacing the Horiz. Output Transistor, it is working fine. The link to the image of the crack point is given below.

http://s1030.photobucket.com/user/ramli7/media/LG29CRTs...

So the first time transistor failure is due to oldness ( 8 years ) of the TV. Subsequent failure is due to this crack of solder point developed during removal of the faulty one.

At this age of 67, it gives me some pleasure to fix this kind of problem..
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