Re: Need help DCLCD 19" LCD Monitor - I already replaced caps
Yes. Screws in and tight.
Yes. Screws in and tight.
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Re: Need help DCLCD 19" LCD Monitor - I already replaced caps
There's a mosfet mounted on the heatsink directly below the large cap. I suggest you check it for shorts.Comment
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Re: Need help DCLCD 19" LCD Monitor - I already replaced caps
Have you had any time to put a check list together of what I should do next?Originally posted by retiredcaps View PostComment
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Re: Need help DCLCD 19" LCD Monitor - I already replaced caps
Check for shorts on the power mosfet as jetadm123 suggested in post #123.Originally posted by DJM_PHX View Post
I have the same smps chip in my monitor. Once I replaced the small cap, I got secondary voltages. See
https://www.badcaps.net/forum/showthread.php?t=9904
for details. If the power mosfet is okay, then the SMPS controller may be bad. Replacements are available on ebay.--- begin sig file ---
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Re: Need help DCLCD 19" LCD Monitor - I already replaced caps
hi, can anyone tell me what the original uF and voltages are on those four caps c114 115 117 and 118 on the LM004 Ver:3 board... thanks
i had replaced the caps a long time ago with caps of higher uF and voltage ratings... and now those went bad after a few years... and i have no idea what the original specs were..Comment
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Re: Need help DCLCD 19" LCD Monitor - I already replaced caps
Check with and ohm meter out of the board, or in the board? Hot or not?Originally posted by jetadm123 View Post
In the board I see resistance but not shorted. I should be able to check voltage on each post by making a probe tip to reach in there.
Also, I can not get to the SMPS control chip while powered up to check it as in the other thread.Last edited by DJM_PHX; 01-03-2011, 05:24 PM.Comment
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Re: Need help DCLCD 19" LCD Monitor - I already replaced caps
I meant to check for shorts with power off.Originally posted by DJM_PHX View PostComment
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Re: Need help DCLCD 19" LCD Monitor - I already replaced caps
Thank you!Originally posted by DJM_PHX View Post
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Re: Need help DCLCD 19" LCD Monitor - I already replaced caps
Originally posted by DJM_PHX View Post
The fluctuating voltage of 10-15V across the 22uf cap indicates that the power supply is trying to start up. Refer to the datasheet application circuit, page 14 regarding the following:
With power off and monitor unplugged,
1) The circuit shows a 56Kohm 1W resistor (your value will be different) connected to the output of the large cap. Find and measure the value of this resistor.
2) In the circuit, you have a 1N3613 diode (your values will be different) feeding the 10uf cap. Locate this diode and check it for shorts.
3) Measure resistance across pins 5 (gnd) and pin 7 (vcc) of the SG3842.
4) You've already checked the mosfet and replaced the small cap.
5) If the above checks good, I have some reservations about the voltage fluctuation on the 450V large cap, you might consider replacing it.
6) If the above checks good, I'm leaning towards replacing the SG3842 chip. It also goes under the part # UC3842 and is dirt cheap, so buy a couple of them.Last edited by jetadm123; 01-03-2011, 09:03 PM.Comment
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Re: Need help DCLCD 19" LCD Monitor - I already replaced caps
Please excuse my ignorance about circuits, but when you refer to "in the circuit", are you talking about in the pdf (which figure) or another diagram? I attached pics of the top and bottom of my boards. It would help if you indicate which is which. I don't see a resistor connected to the large cap, at least what I would recognize a one.
If the diode is on the bottom of the board, D103, I have 99 ohms each way. If on the top of the board I have a D101 and D102. D101 I get nothing in both directions accross it, D102 I get a short beep with no reading but I can flip the leads and get the same result, a short beep. I am not sure what I am seeing.Attached FilesLast edited by DJM_PHX; 01-04-2011, 11:00 AM.Comment
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Re: Need help DCLCD 19" LCD Monitor - I already replaced caps
The applications circuit on page 14 of the pdf file was what I was referring to on my previous post. Since we don't have a manufacturer's schematic to work from, I chose to use the one for the SG3842. Please keep in mind that the SG3842 schematic is a "suggested" design. In reality, your circuit board will differ a little from it. The key is to try and match what you're seeing on SG3842 schematic to what's on your board.Originally posted by DJM_PHX View Post
Either D101 or D102 are probably connected to the positive terminal of your 22uf cap. Since you're getting unusual values from both (I have no idea what a "beep" means on your meter), try removing them from the circuit board and check them again.Comment
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Re: Need help DCLCD 19" LCD Monitor - I already replaced caps
Diodes are best tested with the diode test function on your multimeter. Put red probe on one side, black on the other. Record reading. Now reverse the probes and record reading.Originally posted by DJM_PHX View Post
One reading should be between 0.3 and 0.8V and the other is "1" or 0L (depending on your multimeter).--- begin sig file ---
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Re: Need help DCLCD 19" LCD Monitor - I already replaced caps
The beep tells you if there is a connection and if possible, the Fluke will continue to provide the resistance measurement. I'm using an Fluke 87 DMM.Comment
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Re: Need help DCLCD 19" LCD Monitor - I already replaced caps
On D103 I get 0.058 in both directions. In the above pic, D103 is just above and to a little right of the control chip (orange and black). D101 a 0.462 and OL, D012 returns a 0.441 and OL.Comment
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Re: Need help DCLCD 19" LCD Monitor - I already replaced caps
If D103 tests the same out of circuit, it is bad.Originally posted by DJM_PHX View Post--- 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.
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Re: Need help DCLCD 19" LCD Monitor - I already replaced caps
Nope, not it!Comment
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Re: Need help DCLCD 19" LCD Monitor - I already replaced caps
When I measure between pins 5(Gnd) and 7(Vcc), I see an decreasing meg Ohm resistance. I assume the little cap is charging back thru the ground side of the cap.
Using the diode selection, OL between 5 and 7.Comment
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Re: Need help DCLCD 19" LCD Monitor - I already replaced caps
That's OL with black lead on GND. 0.448 reversed.Comment
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Re: Need help DCLCD 19" LCD Monitor - I already replaced caps
This thread is a long one,One member had a blinkling PLED and found a poor solder joint.It might be advised to check the area where he had problems.Originally posted by hoadle View Post
AlWhatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!
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