help with dead 57uwx20b rear projection


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help with dead 57uwx20b rear projection - PLEASE!!

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tjames72
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Aug 6, 2006, 10:41 PM

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help with dead 57uwx20b rear projection - PLEASE!!	Can't Post

Hi everbody,I posted about a week ago about my 57uwx20b rptv.I've gotten no replies so i'm here to give a little mor info. to see if anyone could help me out.It's a hitachi t.v. The set will come on with the remote but no pic or sound.I can't turn the set off with the remote only by pressing the power button on the set.I checked the fuses and boards for any obvious problems but all checked o.k.The board where the power cord plugs into has 5 led's (4 green 1 red).All led's light except the one on the top right of the board and it's a green led.Can anybody tell me what the problem might be and what that light is supposed to tell.Thanks for any info.

hackman
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Aug 9, 2006, 12:20 AM

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Re: [tjames72] help with dead 57uwx20b rear projection - PLEASE!! [In reply to]	Can't Post

So it’s on, but No HV, or sound?
Warning: HV can injure and/or kill, be careful.
That said, are the Picture Tubes Glowing (There are little filaments on back of each CRT (I hope this is a CRT TV and not a LDP)? Are the tubes glowing? If they are that’s telling us allot, we know we have some voltage coming from the Flyback.
Usually when NO HV or sound, something has 'shorted' out, if vertical gets shorted the TV will refuse Horiz. Deflection , if it didn't there would be a straight line across the screen, and we know if that happens it only takes about 5 mins of vertical line to burn the TUBES, (Same with a Horiz. gets shorted, It may refuse) it only takes about 5 mins before the burn to the TUBES.)
You may need some tools, a schematic would be helpful for this unit, you could your voltages (vertical out, Audio B+ at Amps) Be Careful around Horizontal, you should use a variac, and observe all Voltage warnings in that area (HV can hurt/kill)
If all is checked and is known good, working, there could be something in standby, or deflection yoke shorted.
Observe HV Warnings, and a schematic would help you out!
Anything new, post it.
J. (hackman)
My 2.1 Cents worth.

Larry E
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Aug 11, 2006, 8:41 PM

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Re: [tjames72] help with dead 57uwx20b rear projection - PLEASE!! [In reply to]	Can't Post

the green led that doesn`t light is telling you that the source voltage of that line is dead, look on the inside wall of the set and there will be a paper telling you what each green led`s voltage line is supposed to be, ie; 26 volt or 12v, or 125v, etc. there is a short on that line and depending on which voltage it is will tell us techs what device is probably bad, get back to us with that led`s source voltage, Larry E

tjames72
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Aug 12, 2006, 7:21 PM

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Re: [Larry E] help with dead 57uwx20b rear projection - PLEASE!! [In reply to]	Can't Post

hi larry e.found the paper it read (sw+115).thanks again

Larry E
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Aug 13, 2006, 10:21 PM

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Re: [tjames72] help with dead 57uwx20b rear projection - PLEASE!! [In reply to]	Can't Post

OK, that`s your main B+ line so the most obvious device to be shorted on that line is the horizontal output transistor, take your meter and check the resistance between collector & emitter (C-E) it will most likely be shorted, the little chemical fuse near the green led will also be open most likely, Larry E

tjames72
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Aug 16, 2006, 1:06 AM

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Re: [Larry E] help with dead 57uwx20b rear projection - PLEASE!! [In reply to]	Can't Post

thanks larry -if that fuse is open/shorted does it defintly mean the ho transistor is shorted or is it possible the fuse just opened and if so can i jump across the fuse.i also dont know the value of the fuse.im sorry to keep asking u dumb questions but i belive u are leading me on the right path.you also said to check the resistance on the ho ic between the c and e.what reading should i be getting besides an open or short condition.thanks larry

Larry E
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Aug 16, 2006, 11:07 PM

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Re: [tjames72] help with dead 57uwx20b rear projection - PLEASE!! [In reply to]	Can't Post

tjames, if the chemical fuse is open then something caused it to open, the most likely candidate is the horizontal output transistor, YOU NEVER want to jump out the fuse unless of course you like smoking more parts. The horiz. output is probably on the other board beside the board with the chemical fuses and green led`s that`s why your not finding it, as I said it will be mounted on an aluminum heatsink and it is a large transistor, the voltmeter should read approximately 10K Ohms or more (depends on brand/type of meter) it should show no continuity between emitter & collector (marked e & c on the board) a dead short shows continuity an open device shows high or infinite resistance, the chemical fuse is probably a 4 or 5 amp fuse, usually marked on that sheet of paper on the sidewall of the tv or the fuse itself will have the value written right on it, ie, 4A 125v or 5A 125v etc. Hope this helps, Larry E

tjames72
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Aug 23, 2006, 1:46 AM

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Re: [Larry E] help with dead 57uwx20b rear projection - PLEASE!! [In reply to]	Can't Post

again, i thank you for your time.a couple more questions.i have to remove the transistor from the board to get a correct reading--right?and the board that i see has 2 big ic's with heatsinks--which one is the horiz?im also guessing that the other one is the vertical?these ic's would be mounted on the board with the flyback trans.--right?if im not sure what is what should i just replace both and are they costly?larry im just at the begining to understand how these circuits work let alone how to remove and resolder these ic/fuses.if you suggest to replace both ic's and the pico fuse im a little nervous because im a begginer at soldering.also i would have to remove these boards and i dont know how to remove the hv leads from the flyback trans. and would voltage still be present because the set hasnt been on for a week.will the caps still be charged? and if so how do i discharge them.thanks again i wouldnt blame you if you told me to give up and call a tech because im too inexperienced

Larry E
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Aug 23, 2006, 2:17 PM

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Larry E
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Aug 23, 2006, 2:26 PM

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Re: [tjames72] help with dead 57uwx20b rear projection - PLEASE!! [In reply to]	Can't Post

tjames, your horiz. output should be marked Q777, it`s usually behind the flyback transformer on most sets mounted on a heatsink, check it in circuit c-e if it reads short then you have to unsolder it and check it again c-e to make sure the transistor is shorted not the actual traces on the board, chemical fuse has to be unsoldered to replace it so you need to make a decision, ps the anode lead would only have to be removed if you can`t loosen a few ties and turn the deflection board over, Larry E

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