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#59172 - 11/28/05 10:35 PM electronic question  
lamplighter  Offline
Joined: Oct 2005
Posts: 101
I was told to seek PaulUK for this but, I figured the more the merrier.
My electronics background is all but non-existant and I have a projection style tv that needs help.
The TV is a Sony, XBR 46 inch projection tv.
The symptom is that it will not turn on when the button is pushed and the stand-by led never comes on.
The set shows a definate load when you plug it into the wall and you can hear a small "click" when you do so. It also clicks once about two seconds after you unplug it.
I've had the thing completly opened up and found no sign of anything cooked, not even an odor.
I found 5 fuses in it, all are still good.
Anyone have any ideas as to what I should check first?

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#59173 - 11/29/05 08:20 AM Re: electronic question  
pauluk  Offline
Joined: Aug 2001
Posts: 7,520
Norfolk, England
It sounds like a problem in the power supply section, but without having a circuit or any details of the design of the unit, it's going to be very hard to suggest anything beyond what you've done already, i.e. check for fuses, obvious overheated components, etc.

#59174 - 11/29/05 09:53 AM Re: electronic question  
gfretwell  Offline

Joined: Jul 2004
Posts: 9,057
It is real hard to define the "power supply" section. These things are just one big series circuit. The flyback ends up being the primary for a switcher supply that provides the rest of the DC voltages. The fusible resistor you find blown open is the symptom, not the cause.
I suppose there are people who fix these things but it is beyond me. A "Sony" guy probably just knows which part is bad and replaces it ... but the "FRU" may be a $400 board. I look at TVs the same as Bic lighters. When they stop working I toss them, unopened. The service contract is just the gamble you make. It is a crap shoot. They make so much money on these contracts that they can afford a $400 part now and then.

Greg Fretwell

#59175 - 11/29/05 10:10 AM Re: electronic question  
Mike Wescoatt  Offline
Joined: Jun 2001
Posts: 161
Cedar City, Utah
Check out the large capicitors on the board. They can go bad in under 5 years. The electrolite dries up and then the con't "capicit"or anything else... One of my TV tech friends taught me that and I've repaired three TV's this way. $10 in caps and some time might... might, save the trip to the TV hospital. (Just make sure all of the caps are drained, and not by shorting them out which can damage the delicate IC's inside.)

Mike Wescoatt

#59176 - 11/29/05 07:29 PM Re: electronic question  
NJwirenut  Offline
Joined: Sep 2001
Posts: 806
Bergen County, NJ
Check the large power transistors, as well. Particularly the horizontal output and power supply regulators, and any fusible resistors in these circuits.

Without a schematic and a good knowledge of troubleshooting, you can easily throw many parts at this kind of a problem without getting anywhere.

#59177 - 11/30/05 01:12 PM Re: electronic question  
lamplighter  Offline
Joined: Oct 2005
Posts: 101
It's sounding more and more like I need to have one of my electronic tech buddies look at this thing.
My knowledge in electronics is limited to "Fundamentals of Electronics" back in highschool. Even if that class were advanced enough to help me in this case, which I'm positive it wasn't, I'm sure things have changed in the industry so much in the last 20 years that I'd be lost now anyway.

#59178 - 11/30/05 02:27 PM Re: electronic question  
Dnkldorf  Offline
Joined: Dec 2004
Posts: 1,064
nowhere usa
This sounds like a good enough reason to buy a new LCD, Or DLP to me..........


#59179 - 11/30/05 07:55 PM Re: electronic question  
JoeTestingEngr  Offline
Joined: Nov 2005
Posts: 782
Chicago, Il.
OK, you're probably going to have at least 3 power supplies on your board. One simple linear one that powers your remote control receiver and any smarts in the unit. It will probably use a relay to switch in a 2nd, switching supply to develop several higher voltage (and possibly "diode or" with the output of the linear supply with a slightly higher voltage thus unloading it) Your H.O.T. and flyback will still produce your high voltage and focus supplies, perhaps other boosted supplies.
Checking from the line input, you will probably encounter some spark gaps, a line fuse and a hash filter(looks like a small power transformer, used to keep switching noise out of the AC line). Then, you will most likely encounter a relay that leads to a bridge circuit and some large electrolytic caps. Your relay is probably never picking if you don't have a standby supply. Look for a foil path after the input fuse and before the relay, to a small power transformer. It should only have 4 or 5 pins on it. I would bet a donut that 1.)Your secondary isn't producing an output OR 2.)Your diode, filter, regulator, or crowbar ckt has failed. If you lose the paths from the input, you might want to try searching from the front of the board where the IR receiver is located.
I had a friend bring me a TV and VCR once when the utility had lifted his neutral. The TV had an open primary in said transformer.
Feel free to email.

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