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Dell 1707FPt No Power
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Re: Dell 1707FPt No Power
Originally posted by maybenever View PostChemi-con KY
My "downstairs" computer has an used Corsair PSU with KY caps inside.--- begin sig file ---
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Re: Dell 1707FPt No Power
Well, either something is dragging down the 5V or something is failing, but not outright failed.
You could try replacing the caps, but I don't know if that will fix it.
I spent 20 months tracking down a shorted 5V rail. See
https://www.badcaps.net/forum/showthread.php?p=114994--- begin sig file ---
If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.
We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.
Please do not post inline and offsite as they slow down the loading of pages.
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Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
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Re: Dell 1707FPt No Power
budm Re:
Please test Q107, 108.
What does D802 do? Markings are U4K8 80R K468. When my voltage is steady at output pin, I can track 123vac from power cord connector to this rectifer (I think that is what it is), beyond it I get 185v (I assume it's ac). When the 5.25v output starts droping, this voltage also drops, to like 75v, also the voltage across the large filter cap drops to 48-50 volts. Am I on to anything here.
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Re: Dell 1707FPt No Power
Originally posted by maybenever View PostWhat does D802 do?
http://en.wikipedia.org/wiki/Diode_bridge
Markings are U4K8 80R K468. When my voltage is steady at output pin, I can track 123vac from power cord connector to this rectifer (I think that is what it is), beyond it I get 185v (I assume it's ac). When the 5.25v output starts droping, this voltage also drops, to like 75v, also the voltage across the large filter cap drops to 48-50 volts. Am I on to anything here.
All your measurements at the bridge rectifier should be DC volts. When you are on the hot side of the power supply, the negative leg of the large filter capacitor is ground.
Bridge rectifiers, when not working, are usually shorted and will blow the fuse right away.--- begin sig file ---
If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.
We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.
Please do not post inline and offsite as they slow down the loading of pages.
--- end sig file ---
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Re: Dell 1707FPt No Power
"When the 5.25v output starts droping, this voltage also drops, to like 75v, also the voltage across the large filter cap drops to 48-50 volts. Am I on to anything here."
Is the voltage on the large cap being measured right at the two legs of the cap? Fot it to drop that much, the load has to be tremendous which should have blown the main fuse, that large cap should be able to hold staedy since the inverter is not even running. The voltage on that cap should be around 165~170vdc.Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
Comment
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Re: Dell 1707FPt No Power
Originally posted by budm View Post"When the 5.25v output starts droping, this voltage also drops, to like 75v, also the voltage across the large filter cap drops to 48-50 volts. Am I on to anything here."
Is the voltage on the large cap being measured right at the two legs of the cap? Fot it to drop that much, the load has to be tremendous which should have blown the main fuse, that large cap should be able to hold staedy since the inverter is not even running. The voltage on that cap should be around 165~170vdc.
Is my mosfett bad Q107?
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Re: Dell 1707FPt No Power
I expect that large cap top be bad, if it is is bad MOSFET that draws too much curent, it will be either shorted out or not switching, but it is able to drive the transformer to produce 5v out put, it means it is swithcing but the 168V power supply is not steady to supply the constant voltage.
Is your meter True R.M.S? If it is, put it in AC mode and measure AC ripple voltage on the two legs of that large cap.Last edited by budm; 02-08-2013, 03:22 PM.Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
Comment
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Re: Dell 1707FPt No Power
Originally posted by budm View PostI expect that large cap top be bad, if it is is bad MOSFET that draws too much curent, it will be either shorted out or not switching, but it is able to drive the transformer to produce 5v out put, it means it is swithcing but the 168V power supply is not steady to supply the constant voltage.
Is your meter True R.M.S? If it is, put it in AC mode and measure AC ripple voltage on the two legs of that large cap.
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Re: Dell 1707FPt No Power
OK, so now the 5V is steady and the 168v is also steady, then it is OK, you had indicated that it was dropping like a rock. Now we need to find out if you do have 12~18vdc feeding the inverter section or not. Check the voltage on jumper J117 (or on C811 LEGS) and ground to see what you have.Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
Comment
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Re: Dell 1707FPt No Power
Originally posted by budm View PostOK, so now the 5V is steady and the 168v is also steady, then it is OK, you had indicated that it was dropping like a rock. Now we need to find out if you do have 12~18vdc feeding the inverter section or not. Check the voltage on jumper J117 (or on C811 LEGS) and ground to see what you have.
Comment
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Re: Dell 1707FPt No Power
I need to know if we do have B+ for the inverter circuit first.Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
Comment
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Re: Dell 1707FPt No Power
Now we need to find out if you do have 12~18vdc feeding the inverter section or not. Check the voltage on jumper J117 (or on C811 LEGS) and ground to see what you have.
Comment
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Re: Dell 1707FPt No Power
Originally posted by maybenever View PostIt was dropping, until did all that reflowing.
Do more testing before changing out the caps. As I said before United Chemi-con KY and Rubycon are generally good caps.--- begin sig file ---
If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.
We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.
Please do not post inline and offsite as they slow down the loading of pages.
--- end sig file ---
Comment
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Re: Dell 1707FPt No Power
Originally posted by maybenever View PostTest on Q107, lower pins left to right, pins 1 thru 3 = open, pin 4 = 1615ohm
Test on Q108,""""""""""""""""""""""""""""""", pins 1 thru 4, all = 1610ohm
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Re: Dell 1707FPt No Power
At least now we know we have steady but voltage for the inverter seems high for 17" monitor. But at this point we need to get your main board working again. I would retrace your works to find out what happen now that you have no control, no LED.Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
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