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Old 01-02-2011, 06:08 AM   #41
printone2
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Default Re: Dell 1905FP Powers on then black

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Originally Posted by retiredcaps View Post
The readings for the voltage regulator look fine for part 1084-33. The 0V DC is the adj pin according to the datasheet.
Thanks. I will just wait for the new caps and start from there.
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Old 01-09-2011, 08:36 AM   #42
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Default Re: Dell 1905FP Powers on then black

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I am trying to review things. The monitor will power on and we see a 2 second to black problem .The 5 volts stays constant to the logic board. We see a good backlight on signal when the backlights are on, but when the backlights go off the backlight on signal goes to a low voltage, and no image is visible at any time when a bright light is shined at the LCD screen.
To me it is looking like logic board is not recognizing a valid video signal. I do not think you are measuring the voltage regulators correctly.
If my interpretation of you problem is correct and the next test we should do is verify proper operation of the voltage regulators, I am going to ask one of the other members to guide you through it.
Al
I have recapped the large caps on the IPS and retested the voltage on the backlight enable pin. It now shows 3.3 volts when the lamps turn on and the voltage stays there when they go off. I am not sure if I tested it wrong last time or if the new caps made a difference. Either way the lamps continue to give me 2 seconds to black. I did not change the small caps on the IPS or any on the image card.

I retested the lamps two at a time on another panel. The other panels lamps did not appear to light, but the 1905FP did light with a dim panel since only half the lamps are plugged into it. Same result of 2 seconds to black.

I will recap the larger caps on the image card next and see if results change.
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Old 01-09-2011, 10:49 AM   #43
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Default Re: Dell 1905FP Powers on then black

I have recapped both boards with panasonics and still the same results 2 seconds to black.

I believe I have tested the ccfls to be good. Since I have already swapped a known good IPS I do not think that testing that board further makes sense. The voltage regulator on the image card tested good. I am running out of ideas. I have read Plainbills seconds to black troubleshooting several times and understand most of the ideas. Am I overlooking something obvious?
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Old 01-09-2011, 12:06 PM   #44
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Default Re: Dell 1905FP Powers on then black

If you get the enable voltage going from the Logic card, to the PSU/Inverter PCB, and that stays on IRRESPECTIVE of whether you can see an image or not....AND the Logic card obviously detects the input from a PC,otherwise you would get no Enable on voltage, then 'I will throw all my toys out of the cot' if the fault is not either the CCFLs(one or both), or the Board.As you could not carry out the suggestion in Post 30,then I would measure and compare the resistance of the secondaries of the 2 identical transformers,next to the lamp sockets,they are usually the pins near to the sockets.
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Old 01-09-2011, 01:45 PM   #45
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Default Re: Dell 1905FP Powers on then black

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If you get the enable voltage going from the Logic card, to the PSU/Inverter PCB, and that stays on IRRESPECTIVE of whether you can see an image or not....AND the Logic card obviously detects the input from a PC,otherwise you would get no Enable on voltage, then 'I will throw all my toys out of the cot' if the fault is not either the CCFLs(one or both), or the Board.As you could not carry out the suggestion in Post 30,then I would measure and compare the resistance of the secondaries of the 2 identical transformers,next to the lamp sockets,they are usually the pins near to the sockets.
I have been going over your response and love "the throw all my toys" line, once I looked it up. I think I get it now. I too am still suspect of the CCFLs, but could use some other ideas on how to test them. I am going to attempt your suggestion about the battery power to backlight enable in Post 30. I am giving it some thought.
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Old 01-09-2011, 02:26 PM   #46
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Default Re: Dell 1905FP Powers on then black

Ideally you need 2 known,good, lamp assemblies,and not enclosed inside some screen, but loose,and then see what happens,it may well be if the fault is the output circuit of one of the lamp sockets that you will only see one side lighting up.
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Old 01-09-2011, 07:40 PM   #47
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Default Re: Dell 1905FP Powers on then black

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I have been going over your response and love "the throw all my toys" line, once I looked it up. I think I get it now. I too am still suspect of the CCFLs, but could use some other ideas on how to test them. I am going to attempt your suggestion about the battery power to backlight enable in Post 30. I am giving it some thought.
I came up with a way to give 3volts of power, but with the image card unplugged, but could not figure out how to switch on the mains, since they are switched through the image board.

I do not have two loose lamps to test with.
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Old 01-10-2011, 01:52 AM   #48
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Default Re: Dell 1905FP Powers on then black

You do not need the image board to switch on.Just plug the mains in(being very careful of course),and that works all functions of the PSU/Inverter Board..EXCEPT the Inverter side..ie the Lamps.You then switch them on by applying the voltage.
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Old 01-15-2011, 02:04 PM   #49
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Default Re: Dell 1905FP Powers on then black

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You do not need the image board to switch on.Just plug the mains in(being very careful of course),and that works all functions of the PSU/Inverter Board..EXCEPT the Inverter side..ie the Lamps.You then switch them on by applying the voltage.
Rtech, I did the procedure in post #30 and unplugged the image card. I plugged in the mains and applied 3.1 volts to the backlight enable and ground. The lamps did not light at any time. The power came from a small wall wort with regulated and adjustable DC power. Before I hooked up I verified that I was getting 3.1v. The positive was applied to the bck en wire and the negative to a ground on the connector that joints the IPS and the image card. I also tried it with the ground on the main ground as the power comes into the board. Neither attempt allowed the lamps the come on. I did what I could to verify my connections were good. Thanks.
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Old 01-16-2011, 12:15 PM   #50
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Default Re: Dell 1905FP Powers on then black

So the problem is the board then ..
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Old 01-16-2011, 02:28 PM   #51
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Default Re: Dell 1905FP Powers on then black

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So the problem is the board then ..
I may have just taken two steps back. I hooked up all four lamps to another panel that I suspected had good lamps, but I did not know for sure. Now I get some sizzle from the blue film capacitor labeled c119 on the IPS when I go back to the lamps that are in the original panel.

I was never able to get any lamps outside of the originals ones to light up, so I was making one more attempt to check out the lamps. The other good lamps that I had tried earlier were part of a panel with three pairs of lights and this broken panel has only two pairs. I thought that the difference in the lamps themselves might have been the reason that I could not get them to light. Have I made matters much worse?

What has my rash decision likely to have broken to make a blue film cap to sizzle? The IPS will still turn the lamps on, but it sizzles while they are on and then they go off after 2 seconds.
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Old 01-16-2011, 02:53 PM   #52
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Default Re: Dell 1905FP Powers on then black

Hi, I'm working on the same power/supply inverter board for a Dell 1704FPT. I noticed something very strange about those 2 small capacitors in the inverter. Check to see if one isn't 2.2uf 50v and the other isn't 22uf 50v.
I'm thinking those 2 capacitors should match since one controls the top set of CCFL's and the other controls the bottom. Everything else in the inverter section is matched on both. Transformers, resistors, transistors. BUT with those 2 capactors, one is 2.2uf and the other is 22uf. No wonder so many people are having trouble with that board. I bought a new board and it also has the 2.2uf and the 22uf. Last one burned out after 6 hours. This appears to be a printing mistake that was taken all the way into manufacturing. I may be wrong. But I think this is a possibility.
Now the question for me is.....which one is correct? I believe it's the 2.2uf 50v and they need to be matching.
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Old 01-16-2011, 03:22 PM   #53
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Default Re: Dell 1905FP Powers on then black

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Originally Posted by Lumberjack777 View Post
Hi, I'm working on the same power/supply inverter board for a Dell 1704FPT. I noticed something very strange about those 2 small capacitors in the inverter. Check to see if one isn't 2.2uf 50v and the other isn't 22uf 50v.
I'm thinking those 2 capacitors should match since one controls the top set of CCFL's and the other controls the bottom. Everything else in the inverter section is matched on both. Transformers, resistors, transistors. BUT with those 2 capactors, one is 2.2uf and the other is 22uf. No wonder so many people are having trouble with that board. I bought a new board and it also has the 2.2uf and the 22uf. Last one burned out after 6 hours. This appears to be a printing mistake that was taken all the way into manufacturing. I may be wrong. But I think this is a possibility.
Now the question for me is.....which one is correct? I believe it's the 2.2uf 50v and they need to be matching.
Yes my IPS board has 2.2uf 50v and 22uf 50v. I replaced all the caps with like specs and so these are new Panasonics of the same values that were on the original. Your logic seems sound. I have a 1704FP? that I believe to be a good working panel, but I have not used is for any length of time yet. I believe those machines do share the same IPS model, but the panel is closed up for now. Now you make me concerned about doing any burn-in time on the 1704. I hope someone can give us a second opinion on your hypothesis. I find it hard to believe that something like that could happen, but then I just was reading one of the warnings on another IPS about the "hight voltage" marked in several places on the IPS board, so a misplaced decimal point may not be so odd. But the person doing the assembly would have to make sure they were putting two different caps in the correct places. If they had any experience at all I would think someone would consider it odd. Nonetheless those markings on those small caps is very small and maybe the assembly line is intimidated by the design group. I expect that kind of social interaction is even more prevalent in China.

What makes you believe the 2.2uf is the correct one?

Last edited by printone2; 01-16-2011 at 03:39 PM..
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Old 01-16-2011, 03:53 PM   #54
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Default Re: Dell 1905FP Powers on then black

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What makes you believe the 2.2uf is the correct one?
Because on both boards the resistor at R125 was somewhat fried. And on both boards it was the side of the inverter with the 22uf 50v. I'm not an expert. I'm still learning. But those two capacitors would HAVE to be matching! Everything else is matched. Maybe a professional could chime in on if those caps should match. And which one is correct. The 2.2uf 50v or the 22uf 50v.
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Old 01-16-2011, 09:35 PM   #55
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Default Re: Dell 1905FP Powers on then black

***Update*** It worked! (now we'll see if it passes the burn in phase)

Here's what fixed it......

1. Replaced capacitor at C112 (the 22uF 50v) with a 2.2uF 50v

2. Replaced the transformer at T102. (ring tester showed primary had shorted)

3. Replaced resistor at R125 (even though it tested good, it had really gotten hot and the whole area was brown) This is probably optional

Apparently what has happened is that the manufacturer of these IPS boards lost a decimal point somewhere along the way and started installing a 22uF 50v instead of the 2.2uF 50v. The 22uF by not having the proper microfarad rating slowly burned out the transformer at T102. And the resistor at R125 definitely shows the problem by overheating.

Ok my friend. I'll let that monitor stay on all night and get back with you tommorow. But I'm 99.9% sure it's going to be fine now
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Old 01-17-2011, 03:20 AM   #56
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Default Re: Dell 1905FP Powers on then black

Interesting,and nothing surprises me any more,so might be the answer to both your problems,and 'printone', will be delighted, and I hope the experience will be 'enlightening'........
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Old 01-17-2011, 07:13 AM   #57
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Default Re: Dell 1905FP Powers on then black

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Originally Posted by Lumberjack777 View Post
***Update*** It worked! (now we'll see if it passes the burn in phase)

Here's what fixed it......

1. Replaced capacitor at C112 (the 22uF 50v) with a 2.2uF 50v

2. Replaced the transformer at T102. (ring tester showed primary had shorted)

3. Replaced resistor at R125 (even though it tested good, it had really gotten hot and the whole area was brown) This is probably optional

Apparently what has happened is that the manufacturer of these IPS boards lost a decimal point somewhere along the way and started installing a 22uF 50v instead of the 2.2uF 50v. The 22uF by not having the proper microfarad rating slowly burned out the transformer at T102. And the resistor at R125 definitely shows the problem by overheating.

Ok my friend. I'll let that monitor stay on all night and get back with you tommorow. But I'm 99.9% sure it's going to be fine now
I look forward to your successful reply.
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Old 01-17-2011, 07:26 AM   #58
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Default Re: Dell 1905FP Powers on then black

Well I finally realized that I have a good IPS in a working panel, but have been testing this broken panel with ccfl lamps from a very different panel. This broken panel has four lamps, but I was testing it using a panel that had six lamps. Now that I see how the lamps are wired, I realize that what I thought was a known good set of lamps may have some problems of its own.

I swapped the IPS with the known good IPS and it also sizzled, so now I can say for certain that the problem is with the lamps or wiring to the lamps.

I next tried both IPS boards in the broken panel but using the lamps in the known good panel, even though these lamps are 17" instead of 19". The 2 seconds to black panel is able to keep the known good lamps on for as long as I want.

By connecting the suspect lamps with the some of the good lamps, I narrowed it down to one lamp. After opening the panel to get to the lamps, I see that one of my lamps is snapped in two. Well the mystery is solved for me. Now I just have to decide if I can replace a lamp or not. I will look for instructions and advice on that part of the task.

Thanks.
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Old 01-17-2011, 08:18 AM   #59
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Default Re: Dell 1905FP Powers on then black

[QUOTE=printone2;146312 Now I just have to decide if I can replace a lamp or not. I will look for instructions and advice on that part of the task.

Thanks.[/QUOTE]

I think you have already done the hard part, by disassembling the LCD panel.
Do your best to try to salvage the silicone end caps. Some lubrication works wonders.
Do not increase the length of the ccfl tubes, and use solder very sparingly. And do not force anything.
Dust can be a big problem so look closely during assembly.
Al.
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Old 01-17-2011, 11:23 AM   #60
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Default Re: Dell 1905FP Powers on then black

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I think you have already done the hard part, by disassembling the LCD panel.
Do your best to try to salvage the silicone end caps. Some lubrication works wonders.
Do not increase the length of the ccfl tubes, and use solder very sparingly. And do not force anything.
Dust can be a big problem so look closely during assembly.
Al.
What lubrication do you suggest and is that to get the end caps off/on or both? I think I can come up with some synthetic grease that is dielectric and good up tp 450 degrees.
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