Dell 2007WFP Won't Power On

[PlainBill]

Re: Dell 2007WFP Won't Power On

Yes I did measure all 4 the j598s, I get 19v to both the legs on all them. The row of fuses stamped with "G" have no voltage getting to them.

The tab is the third terminal of the J598s. I had assumed you checked those and found 0 volts.

PlainBill

[alexanna]

Re: Dell 2007WFP Won't Power On

There is a center pin it's the tab.
This picture may be easier to read the voltages.

[croket]

Re: Dell 2007WFP Won't Power On

Yes that's correct, I get 0v to the tabs, only voltage is on the 2 soldered legs

[PlainBill]

Re: Dell 2007WFP Won't Power On

A couple of thoughts. It would seem there must be a common failure OR one of these regulators is a 'master' regulator. It isn't possible to check the outputs of the TL1451As without a scope, but a short on one of the flyback diodes (FD1, FD2, etc) on the (supposed) master regulator would shut everything down. There are 8of these diodes, check them all.

PlainBill

[croket]

Re: Dell 2007WFP Won't Power On

Hey Plainbill,

I tested all 8 diodes and here are my readings. With my DMM set to diode, I placed the black lead to the cathode side and the red lead to the anode, on all the diodes I'm showing 137 on my DMM. When I reverse the leads I get numbers climbing up in the hundreds then changes to a single 1, in other words 200s,400s,900s,1600s,1900, then 1.

They all do this with the exception of 2 of them, Fd7 & Fd8. With the leads reversed, the the numbers climb and stop at 1054 every time.

Don't know if I'm reading them correctly because they are on the board, perhaps I'm reading through the board and not getting a good reading but so far that the only difference I've been able to find.

[PlainBill]

Re: Dell 2007WFP Won't Power On

Hey Plainbill,

I tested all 8 diodes and here are my readings. With my DMM set to diode, I placed the black lead to the cathode side and the red lead to the anode, on all the diodes I'm showing 137 on my DMM. When I reverse the leads I get numbers climbing up in the hundreds then changes to a single 1, in other words 200s,400s,900s,1600s,1900, then 1.

They all do this with the exception of 2 of them, Fd7 & Fd8. With the leads reversed, the the numbers climb and stop at 1054 every time.

Don't know if I'm reading them correctly because they are on the board, perhaps I'm reading through the board and not getting a good reading but so far that the only difference I've been able to find.

The behavior of the first six is normal. I would say that the behavior of FD7 and FD8 indicates something is different on that supply and is a clue that there may be a problem.

If you have a variable output power supply, I would CAREFULLY increase the voltage on the cathode end of the diodes while monitoring the current. If this is a 'hard' limit, there definitely is a problem. Alternatively, test the diodes out of circuit and also see if you get the same effect on the solder pads with the diodes removed.

PlainBill

[Dampil]

Re: Dell 2007WFP Won't Power On

Hi to all
I have 2 monitors with same problems. I take off FD7-8 diods and test it without circuit - it work properly. Between diods pads on textolite are the same 1000-1200 ohms. Then i take and tested U2, Q14, C60, C44, C66 without circuit - it's all look properly.
Else i said that parasitic resistance sensitivy to temperature - during heating it reduced to 50 - 100 ohms. During cooling, it returns to 1000-1200 ohms.
May be that problem between layers of textolite? Which element can change the resistance to such limits as a function of temperature?

I apologize for my English - it very bad.

[croket]

Re: Dell 2007WFP Won't Power On

Well I think I ran out of luck, I removed FD7 and FD8 and they tested ok, (got very similar reading as the others) the pad for FD8 was showing fluctuating readings so I removed the neighboring cap (C60) hoping that would stop the flocculation but it didn't.

I then soldered everything back in and it was back to square one, Until.... I kept probing around with my meter leads and I guess I must have accidentally shorted out a solder joint with another because now I Lost my F19, I get 18v on one side and not the other. So now I got NO voltage passed F19..
I think its time to start shopping for another USB board or another Monitor.

[croket]

Re: Dell 2007WFP Won't Power On

Hey guys, just thought I'd give you an update, I purchased another working usb board and reassembled all the boards onto the frame along with the LCD panel. I plugged it in but yet again it doesn't turn on. not even the orange led power light came one.

I took the LCD panel off, Upon doing so I felt the logic board and noticed that it was unusually warm.
I stripped all the boards off the frame and just left the logic board attached to the New USB board. I then plugged in the power cable, immediately the Genesis chip on the logic board began warming up and getting hot to the point where it will burn your finger.

No "snap crackle or pops" anywhere just the hot chip.

[shavelieva]

Re: Dell 2007WFP Won't Power On

Any more updates?

So has it been established tat for sure the USB board is a required component?

[shavelieva]

Re: Dell 2007WFP Won't Power On

Soo.. Impatience/stupidity struck so I decided to jump the 3A fuse on the USB board which cause the resistor connected to pin 3 to glow.... I'll get a picture up later.

[LAS]

Re: Dell 2007WFP Won't Power On

So this week, I became the proud owner of a Dell 2007WFP that has no signs of activity at all, and the power indicator light does not work either. I have spent some time during the past couple of evenings reviewing some of the troubleshooting above, and I believe I am heading in the right direction but request the benefit of the collective list experience to finish it. I have attached a photo of the logic and USB boards, and in summary:

Fuse F19 on the usb card (circled) was blown. I replaced it with another inline fuse, and optimist that I am, I put it all back together and hoped for the best. Well, it didn't work. I do however have 19v at the base of the fuse, but now that it is blown again, the voltage gets no farther.

Diodes FD3 and FD4 (circled) on the usb card are shorted and less than an ohm across them and in both directions. Can these be replaced with a regular 1000v diode that I have in my spares box? Or do I need special smd ones?

On U13 on the logic card (circled), the first and third pins have 82 ohms across them. Shorted?

On U5 on the logic card (circled), the first and second pins have 82 ohms across them. Shorted?

Can anyone recommend anything else to check? Or should I put those generic diodes and a new fuse on the usb card and give it another try?

[budm]

Re: Dell 2007WFP Won't Power On

19VDC feedind USB HUB board sound kind of high since USB uses 5VDC max. You may want to trace that voltage connections to see if it goes back the power supply board.
Those two diodes look like they are part of the switching power supply, so more likely to be Schottky Diode, you may want to check that MOSFET next to it to see if it is shorted out.
The two linear regulators, we need the numbers, more likely you are measuring the resistor network resistance for setting the output voltage.

[retiredcaps]

Re: Dell 2007WFP Won't Power On

Fuse F19 on the usb card (circled) was blown.

Diodes FD3 and FD4 (circled) on the usb card are shorted and less than an ohm across them and in both directions.

On U13 on the logic card (circled), the first and third pins have 82 ohms across them. Shorted?

On U5 on the logic card (circled), the first and second pins have 82 ohms across them. Shorted?

Can anyone recommend anything else to check?

Welcome to the club. I have the exact same monitor with the exact same 5 bad components.

[retiredcaps]

Re: Dell 2007WFP Won't Power On

19VDC feedind USB HUB board sound kind of high since USB uses 5VDC max. You may want to trace that voltage connections to see if it goes back the power supply board.

If I remember correctly, the power board only puts out 19V DC. My boards have been sitting for almost year awaiting repair and tools.

Scary, that these Dells are failing the exact same way.

[budm]

Re: Dell 2007WFP Won't Power On

I will look and see if i have any 2007 at the recycle place tomorrow, then I can see how it is put together.

[retiredcaps]

Re: Dell 2007WFP Won't Power On

I will look and see if i have any 2007 at the recycle place tomorrow, then I can see how it is put together.

This photo in post #7 in this thread shows the layout.

https://www.badcaps.net/forum/attach...9&d=1281621880

[budm]

Re: Dell 2007WFP Won't Power On

I look through the posts, so this monitor only has one DC supply that supplies 19Vdc for ALL circuits, now I can why there are so many Buck regulators on the USB board which also supply 12vdc for the powered speaker sound bar.
Yes, it is strange that the two Diode for the buck regulator shorted out when they only see 19Vdc reverse bias voltage, I would also think the MOSFET 2SJ598 (P-CH) MOSFET did not blow up when it cycles on and feed those two shorted out Diode, I can see that it will blow the 3A fuse.

[retiredcaps]

Re: Dell 2007WFP Won't Power On

I look through the posts, so this monitor only has one DC supply that supplies 19Vdc for ALL circuits,

While you were posting, I dug up the power board and confirmed that both connectors CN701 and CN702 ouput ONLY 19V DC with my multimeter.

[budm]

Re: Dell 2007WFP Won't Power On

I need to find the spec of the Schottky Diode, S4 64A to find out what the reverse voltage and current handling is.
Never mind, found the answer from your old post:
https://www.badcaps.net/forum/showthread.php?t=20059
1A 40V, pretty low current, so they wire them up in parallel which will not really work well unless they match the Vf perfectly or use resistor to balance them out. I would replace them with 2A or higher instead.