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  #16  
Old 07-06-2016, 06:24 PM
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N2IXK N2IXK is offline
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Those inverter transformers operate at high voltages, and they are prone to insulation breakdown and shorted turns, which then overheat and blow the driver FETs. By the time you source the parts (if you can get them) and install them, you might be best off looking for a used board on eBay.
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  #17  
Old 07-06-2016, 08:48 PM
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A backlight fault on these doesn't shut the power supply down. The set would power up normally with no backlight. The glass diode is a Zener and often shorts on these, from memory it's 5.1V. It will shut down the power supply if it has failed. If it has shorted also replace the 2 10V 1000uF caps (unless they test good with an ESR meter).
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  #18  
Old 07-06-2016, 10:52 PM
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Those are the 2 caps i was talking about replacing, i was thinking of replacing them with 16v ones.. Im uncertain about the zener being shorted, i hook it one way, and the digits begin to climb as if ive hit a capacitor in the circuit. my meter isnt zeroing out when i test it. The numbers are low but not zero... I'll have to test it again to be sure.. Ide hope the backlights are okay, this set has less than 30 hrs on it as stated earlier

SR

Last edited by Boobtubeman; 07-06-2016 at 10:55 PM.
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  #19  
Old 07-07-2016, 12:04 AM
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It is fine to replace the 10V caps with 16V caps. The zener diode will read close to 0 in both directions if it is shorted. Otherwise it will read around 0.7V (using the diode check range on a digital meter) in one direction and open in the other. In circuit other components around it can effect the reading. If you're unsure unsolder one side of it and test again.
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  #20  
Old 07-08-2016, 10:26 PM
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Quote:
Originally Posted by dr.ido View Post
The caps are not that critical in these (there are some exceptions, but not for this board). As long as the voltage rating is at least as high as the original and the capacitance is somewhere near (eg, replacing a 2200uf with 3300uf or vice-versa) it will work. Near the 2 caps near the connectors the zener diode and the to-220 package diode often short in these.

That said, if the 12V rail is coming up at all the short isn't on the 12V rail.

In your set there is a small DC-DC sub-board mounted between the power supply and the tcon board. These can and do fail shorted. If it has failed it could shut down the power supply board, disconnect it and see if anything changes.
Unsoldered a pin on the zener and its not reading a short, The to-220 tests fine on diode position...

SR

Last edited by Boobtubeman; 07-10-2016 at 01:39 AM.
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  #21  
Old 07-10-2016, 01:50 AM
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Went as far as running without the zener and no change. The to-220 tests fine on the diode setting on my meter so its back in circuit. Double checked my voltages and all the + and- 5 volts are present. The 12v pin only gets as high as 3v before it falls due to the instant shut down.. Swapped the 1000uf@10v e-caps with an exact set of used ones. I dont have an ESR meter, I am using a centech #69096 digital meter if that helps reference my tester and its functions...

The dc-dc sub board mentioned gets to 14v before the shutdown...

any other culprits on this board i need to check??

SR
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  #22  
Old 07-10-2016, 06:14 AM
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I don't have one in front of me right now to check, nothing immediately obvious jumps to mind. Have you tested with the 12V line disconnected from the main board to rule out a fault on the main board dragging to down? I've seen this when the audio amp IC fails.
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  #23  
Old 07-10-2016, 05:18 PM
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Mainboard is fused and they check OK, however, i did remove the 12v lines to all and the result was the same. Its definitely within this board somewhere.. I dont know if the 12v rail is okay, it never reaches 12v before shutdown, but i gained 2 volts without a load, meter reaches to 6v before cutoff... Definite head scratcher this one be...

SR
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  #24  
Old 07-10-2016, 10:51 PM
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There's a Zener on the 12V rail hiding between a couple of caps under a blob of silicon on the one that I have on the bench. There's a FET on the bottom of the board but I don't think it's on the 12V rail. I've tried tracing these out further in the past and hit a dead end with the unmarked (or unreadable) SMD parts on the bottom on of the board. At that point you're already into it for more than a 26" LCD TV is worth.

If I get time I'll have another look at the one I have here, I don't remember what was wrong with it.
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  #25  
Old 07-11-2016, 01:24 AM
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No worries... It was a freebie and my first look inside one of these flat screens. Definitely a great learning experience and i appreciate you folks walking me through it. I can see why there are no more tv shops in my town...

Been looking on ebay for the local board offerings and searching for a cheap one, first im gonna exhaust myself on this one before then. Ill check that zener next and do some more poking around..

Thanks..

SR
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  #26  
Old 07-23-2016, 04:13 PM
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Upside??? i did get a board of Ebay...... Downside? My board is in better shape, The replacement i ordered has NO output voltages at all (yes, i confirmed voltage going into it )

Since i dont have an ESR, i think ill make a trip to the store and go FRESH caps for the old board and see what happens..

SR
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  #27  
Old 07-23-2016, 08:02 PM
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Quote:
Originally Posted by Boobtubeman View Post
Since i dont have an ESR, i think ill make a trip to the store and go FRESH caps for the old board and see what happens..
How about a cheapie bare board model?

https://www.amazon.com/Yosoo-Display...W7SKV0QNA8K8G9

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  #28  
Old 07-23-2016, 08:20 PM
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Quote:
Originally Posted by jr_tech View Post
How about a cheapie bare board model?

https://www.amazon.com/Yosoo-Display...W7SKV0QNA8K8G9

not affiliated,
jr
You can get them for half that on the-bay...
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  #29  
Old 07-24-2016, 07:41 PM
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Replaced the 1000uf-10v with 35v ones and still wont come out of standby. Still beats the DOA board i got off ebay

Back to the ole drawing board.......

SR
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  #30  
Old 08-10-2016, 01:21 AM
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Got another board and STILL wont come out of standby.... Any way to kick the power supply on without hooking the tv works up to it? Also i noticed a green led on the power board, in what situation will this light??

SR
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