Dell 2007WFP Won't Power On

[peterfares]

Hello, I have a Dell 2007WFP that will not power on.

What happened was I was plugging into the 12V output on the monitor and accidentally shorted the positive and negative on it. When that happened, the monitor instantly turned off and will no longer power on.

I have taken it apart and I am getting voltage from the power supply, so I do not believe it is the issue. Is there any way to fix a logic board problem?

Thank you.

[retiredcaps]

Originally Posted by peterfares

What happened was I was plugging into the 12V output on the monitor and accidentally shorted the positive and negative on it. When that happened, the monitor instantly turned off and will no longer power on.

Do you see any fuses on the board?

What voltage are you getting on the power supply and where are you measuring it?

For more help, post clear focused pictures using the instructions at

http://www.badcaps.net/forum/showthread.php?t=1868

[peterfares]

Hello,

I am measuring the voltage at the connector going to the logic board. It is showing 18V across the pins in the picture. None of the other pins show voltage relative to any of the other pins on the connector.

There is one fuse I found on the power supply and it has no resistance across the ends.

I will upload more, higher quality photos tomorrow.

Thank you!

[retiredcaps]

Originally Posted by peterfares

There is one fuse I found on the power supply and it has no resistance across the ends.

By no resistance, can you please clarify the actual ohms reading?

[peterfares]

I have a crappy old analog multimeter, but the dial goes below 0, which is also what happens when I touch the two probes together.

[retiredcaps]

Originally Posted by peterfares

I have a crappy old analog multimeter, but the dial goes below 0, which is also what happens when I touch the two probes together.

Thanks for the explanation. Let's wait for the pics tomorrow. Both sides, top down view, of all your boards. Plus an "overall" shot of everything connected would help.

[peterfares]

Here are better quality photos of my boards.

[jetadm123]

Hello! You said that you shorted out the 12v output, which I believe is for your soundbar, correct? If so, this is the card in your first photo sitting to the left of the video/logic card. Check to see if there are any blown fuses on either of these two boards. They would be of the surface mount type. Check both top and bottom of each board.

[peterfares]

Yes it is for the soundbar. What do surface mount fuses look like? The only fuse I know the shape of is the large one on the power supply. I tried putting only the 3 boards in (not the soundbar/USB hub board) but that didn't work either. I don't know if the soundbar/USB hub board does more than just that, though.

I took these photos in a rush and it seems they aren't very good. I will take even better ones later today.

[jetadm123]

It would be a tiny flat rectangular device with metal tabs at each end. It may have a letter or number stamped on it. Check for the silkscreen on the board itself. Fuses are usually identified with FXXX or PFXXX (where XXX is a 1-3 digit number).

[peterfares]

Please take a look at photo 3, at the top right of the logic board. There is a rectangular element with 3 pins on the bottom and one at the top. It looks very weird, sort of like it is slightly melted. I don't know if it is supposed to look like that or not. There is another thing like it on the other board in the same picture, but without the weird melted look.
Is it possible for something to melt like that instantly? It was nearly instantaneous from when I shorted the pins and when the screen shut off.

[jetadm123]

Yeah, I think you found the problem. It looks like it burned out and took the part number with it. Post the silkscreen ID: probably QXXX or UXXX. Hopefully, someone has a schematic or similar board and can help. Also, better quality closeup photos of that part of the board will help others help you.

[retiredcaps]

Originally Posted by peterfares

I took these photos in a rush and it seems they aren't very good. I will take even better ones later today.

Take a look at post #1 on how we would prefer the pictures.

http://www.badcaps.net/forum/showthr...&highlight=cmv

There were taken on a sunny day next to the window. You clearly see all the writing on the PCB especially this one ...

http://www.badcaps.net/forum/attachm...4&d=1280167246

A SMD fuse looks like FP1 (lower left hand corner right by the connectors).

[peterfares]

Alright, I will post higher quality photos when I get back home. I was in a rush this morning so I didn't have time to check the photos and see how they turned out. What can that burned out piece be? Is that a standard package that a lot of things are made to look like?

[retiredcaps]

Originally Posted by peterfares

Please take a look at photo 3, at the top right of the logic board. There is a rectangular element with 3 pins on the bottom and one at the top. It looks very weird, sort of like it is slightly melted.

That is probably a voltage regulator. You can test to see if it is shorted or not using ohms. Turn power off and lcd unplugged.

If you test 1-2, 2-3, and 1-3, they should all read over 100 ohms.

[peterfares]

I tested the burned out piece. The only short is from the top pin to the middle pin on the bottom. The resistance across the pins varies from 5 to 60 ohms and also varies depending on which probe (positive or negative) I touch to which pin.

Here are some very nice quality photos.

[retiredcaps]

Originally Posted by peterfares

I tested the burned out piece. The only short is from the top pin to the middle pin on the bottom. The resistance across the pins varies from 5 to 60 ohms and also varies depending on which probe (positive or negative) I touch to which pin.

Here are some very nice quality photos.

The top pin or tab is usually ground. Pin 2 is probably ground which is why it will read 0.3 ohms.

5 ohms suggests the voltage regulator is shorted and bad. Heck, one look at the picture and most will conclude it is bad. Also cap C57 may have been damaged?

The pics are a HUGE improvement and help a lot. One of the reasons we insist on clear focused pictures is that someone past or future can use these photos to find burnt out parts. So if someone in the past had posted good photos this particular board, we can immediately tell what the voltage regulator is.

Now the key question is what is the replacement part? I'm guess it is some sort of step down like 5V DC to 3.3V DC?

[peterfares]

There is another voltage regulator on the USB board that is 3.3V (960T63). I wonder if they're the same... Also to help anyone in the future, the way to remove the bezel monitor is to pry it off by putting your finger near the actual panel and pulling up on it.

[jetadm123]

NICE PHOTOS!!! Man, that poor chip took a beating! Read all steps before attempting.




We may have to do a little reverse engineering to verify that this device is a voltage regulator:

1) with power off and unplugged, do what retired caps suggested and check the burnt unit for shorts.

2) if shorted, you'll probably have to unsolder the three legs to perform the following tests. Bend the legs out of the way. Don't remove the unit, since someone may have a better idea on testing.

3) familiarize yourself with the wire harness/connector that connect the power, logic and 12v output boards together. Can't tell from the photos, but are any of board connectors labeled with voltage values, etc?

4) on a voltage regulator there are the voltage input(Vin), voltage output(vout) and ground legs. Using your ohmeter, see if you can follow the path from the 18v (or whatever voltage is feeding the logic board) output (there may be more than one output) of the power board to one of the solder pads the burned unit was soldered to. If you can verify connectivity, that's probably Vin.

5) Vout would have you start at the 6 pin connector of your logic board (photo 1) and work your way back to a pad of the burnt unit.

6) On the 12v output board (photo 6) check fuse F19 upper right of 6 pin connector(photo #6) with "3A" stamped on it. U2 looks to be a regulator. Please check that for shorts.

7) The question is why did the fuse or voltage regulator on the your 12V output board (photo 6) not blow or short out first? As a matter of fact, where is it getting the 12V from?

[peterfares]

Originally Posted by jetadm123

6) On the 12v output board (photo 6) check fuse F19 upper right of 6 pin connector(photo #6) with "3A" stamped on it. U2 looks to be a regulator. Please check that for shorts.

The 3A fuse shows 2000 ohms resistance. Is it good or blown? I already desoldered it because I thought it was blown since my dumb multimeter sucks so much.

Also the voltage regulator on the USB board is showing the same resistance as the one that is supposedly fried.

EDIT: Got the fuse back in easily. I thought it would be much more difficult than it was.

EDIT 2: I was able to scrape that gunk off the "blown" voltage regulator and it came off fine. The part doesn't appear to be damaged.

I'm going to attempt to replace the capacitor that appears broken