Dell 2407wfp - No power

[GuySmily]

Hi all,

I have a completely dead 2407WFP here. One day it worked, the next day it didn't.

The monitor won't turn on at all, and the power button doesn't light up.

I pulled the power board to take a look at it, but honestly I don't know what to check for. None of the caps are bulging. No components appear to be burned/leaking/etc.

The solder joints on HS1 look toasty, but Q651, which is attached to it, seems to be just fine:



It also looks like something boiled/burned under C714, but I think it's just leftover gunk from a cleaner or something:



Here are a few shots of the power board:




More pics / higher res here:
https://picasaweb.google.com/1019171...eat=directlink

Any thoughts/suggestions/instructions would be appreciated. I have a multimeter and I know how to check resistance/continuity, but I don't want to start randomly poking at stuff on the board.

[budm]

Re: Dell 2407wfp - No power

What DC voltage on the two legs of that large 450vdc black cap laying on its side? Be careful, you are working in the hot side of the circuit. The little yellow fuses are OK?
http://s807.photobucket.com/user/bud...?sort=3&page=1

[GuySmily]

Re: Dell 2407wfp - No power

I see two fuses. I set the multimeter to beep mode (beeps when I touch the prongs together) - that's good enough, right?

The big fuse by the AC input, F601, gives me a beep.
The little yellow fuse by the 5 caps, F701, also looks good.

No fuses on the bottom side I don't think. Just a few SMD caps/resistors/diodes/etc.

What's the procedure for testing that cap? Do I want to check it while the monitor is plugged in? Currently, I get no voltage reading across the cap (OL). I've never done high voltage stuff before, so I'm wearing goggles/gloves and everything, lol.

edit- Checking out the guide in your sig right now too. Thanks for the quick reply, btw

[budm]

Re: Dell 2407wfp - No power

Monitor plugged and do not touch anything with your hands, If you put black probe on the chassis, red probe on the ends of the yellow fuse F701, do you get about 19VDC?

[GuySmily]

Re: Dell 2407wfp - No power

Yes, 18.9V between chassis and F701 (both legs).

edit - Looked through your pics and read the pdf. Thanks for that.

[budm]

Re: Dell 2407wfp - No power

That mean the main power supply board is OK, there are sub power supply board/main board for producing 12v, 3.3v, etc which is more likely where the problems are. If you look at my pictures, it will show you the test points.

[GuySmily]

Re: Dell 2407wfp - No power

Cool, I'll start checking em out. In all the shots with only one probe shown, the black probe is on the chassis, right?

edit- nm, I guess that's pretty obvious. Just being careful.

0V on everything so far..

edit2-
Ok, 3.23V on this one: http://s807.photobucket.com/user/bud...tml?sort=3&o=5

edit3-
0V going to the T-Con. I won't even open it up unless you think I need to.

[budm]

Re: Dell 2407wfp - No power

Yes, leave the black probe on the chassis, just do not let the red probe slip when you probing those test points.

[GuySmily]

Re: Dell 2407wfp - No power

Cool.

So far, 0V on everything pictured except for 3.23V on FD7 (see edit2, above) and 19V on the inverter fuse F1.

STBY = standby?

Checking your CN702 readings next.

[GuySmily]

Re: Dell 2407wfp - No power

These two connectors match your standby readings:
CN702:
1 = 0V
2 = NC
3 = 1.691V
4 = 18.9V
5 = 18.9V
6 = 18.9V
7 = 0V
8 = 0V

CN701:
1 = 0V
2 = NC
3 = 1.691V
4 = 18.9V
5 = 0V
6 = 0V
7 = 18.9V
8 = 0V
9 = 0V
10 = 0V
11 = 0V

edit - Obviously I can't turn the monitor on, so I can't compare "On" voltages.

I have 0V on these 3.3V VREG:
http://s807.photobucket.com/user/bud...ml?sort=3&o=58

I have 1.789V on this 1.8V VREG:
http://s807.photobucket.com/user/bud...ml?sort=3&o=59

Fuse to speaker jack = 0V

I'm not measuring resistance across the inverter coils yet. Should I unplug the monitor first?

And I think that's everything.

edit- Basically my 3.3V and 5V stuff are showing 0V. What now?

[budm]

Re: Dell 2407wfp - No power

OK, you need that 3.3V, 5V power supply for the logic circuit to run, so that is one of your problem right now, do not worry about the 12VDC, it is for supplying the 12V to run the Dell powered speaker sound bar only. More checking in the 3.3V power supply circuit. Check the diodes, MOSFET.
If you search the forum for Dell 2407, you will get lots of hits.

[GuySmily]

Re: Dell 2407wfp - No power

lol the first thing that came up when I googled "2407wfp diodes" was this thread. Nice job, Google.

I remember seeing a thread a month or two ago where someone checked a million diodes, but I haven't found it since. Will keep looking.

Thanks for all your help!

[budm]

Re: Dell 2407wfp - No power

https://www.badcaps.net/forum/search...archid=3242656 on dell 2407.

[GuySmily]

Re: Dell 2407wfp - No power

Are there any diodes that I can't test on the board by simply checking for continuity in both directions?

For example, with my multimeter in diode mode, I see voltage in both directions in the diode below your probe here:
http://s807.photobucket.com/user/bud...tml?sort=3&o=5

I don't know how diode mode works, but on that diode I see 0.530 volts in one direction and 0.155V in the other.

If I short the two test probes together, I get 0V.

On the 3 diodes by the RCA jacks, I get ~0.58V in both directions.

On a diode between the VGA port and the big Genesis chip, I get 0.8V one way and 0.5V in the other.

On the 9 diodes by the VGA port, I get ~0.6V in one direction only (and OL in the other). One of these diodes shows 10k ohms resistance in both directions though I'll just ignore the resistance and use diode test mode.

edit-
I read this, but can't say that I understand the implications:
http://www.allaboutcircuits.com/vol_3/chpt_3/2.html

[GuySmily]

Re: Dell 2407wfp - No power

Okay, I must have screwed something up earlier. I KNOW I had 0.00V readings (as opposed to the usual -20mV or whatever when there's no connection), but all of a sudden I have readings on all the voltage regulators, and they appear to be correct.
Scroll down to pics with multimeter:
https://picasaweb.google.com/1019171...eat=directlink

Main board voltage regulators:
Q6 - near connector to power board CN701)
Line 1: J598
Line 2: KS 78
Pin 1: 18.97V
Pin 2: 0V
Pin 3: 18.9V

Q1 - beside Q6
Line 1: J598
Line 2: KS 78
Pin 1: 18.97V
Pin 2: 0V
Pin 3: 19.01V

U4 - near white connector to T-Con
J282
952T43
0V
1.79V
3.25V

USB board voltage regulators:
(Too tired.. I'll update this later. Pics are up though. Basically, they all match your pics)

Other:
FD1 and FD2 still read 0V, as does this one pin going to the T-Con

[Davi.p]

Re: Dell 2407wfp - No power

Hi, from the budm pictures i understand nothing, why don't you post a big picture of all the Main Logic Board (MLB)?

[GuySmily]

Re: Dell 2407wfp - No power

Not at home right now, but I did snap a couple pics last night.

First two images at this link:
https://picasaweb.google.com/1019171...eat=directlink

[GuySmily]

Re: Dell 2407wfp - No power

So, I was lowering the main metal chassis cover over the circuit boards, and I shorted something near the 120VAC plug and popped my house circuit breaker. There was a spark and the electricity in all the bedrooms cut off immediately.

I no longer have 19V at F701, but I do have continuity through it.

I lost continuity through F601 (the big fuse beside the 120V socket) though. It says T4AH/250V. What does that mean? Can I just find another fuse and replace it? Also, why would you design a fuse holder that you have to desolder to remove the fuse? Seems kinda pointless.
https://picasaweb.google.com/lh/phot...eat=directlink

I assume it's AC and I've never measured AC voltage before, so I didn't want to try checking it. I assume that lack of continuity is enough to know it's blown.

[budm]

Re: Dell 2407wfp - No power

You blew the main AC fuse, it is 4A Time-delayed type fuse, 250V rating.

[SkOrPn]

Re: Dell 2407wfp - No power

So, I was lowering the main metal chassis cover over the circuit boards, and I shorted something near the 120VAC plug and popped my house circuit breaker. There was a spark and the electricity in all the bedrooms cut off immediately.

Old thread I know, but still I am curious if you ever managed to repair your Dell monitor? Since you never did post any more replies it makes it seem you gave up on it. If not, what did you learn about your Dell 2407wfp?

I am in research and planning phase to repair mine, so please understand why I am asking.

Rod