Dell 2007 fpb 2 seconds to black. Almost solved.

[toli0002]

Background;
- A Dell 2007 fpb thats restarts (cyclic) after 5-8 seconds.
- A Dell 2007 fpb that works!

First! It is the USB board that fails! (for me...)

I have read very good threads, thank's budm and others!
(Hope it's ok that I borrowed your image budm?!)

Dell 2007FPB teardown
https://www.badcaps.net/forum/showth...07fpb+teardown

A guide on how to troubleshoot 2 seconds to black
https://www.badcaps.net/forum/showthread.php?t=10419

Comparing measurements between the good and bad monitor is showned in the attached images of the USB board and Logic board.

When switching USB boards the problem follows. Measuring the 3.3 Volt shows a bad reading 0 to 3.3V cycling which follows the screen behavior!

Caps on the USB board are replaced without success.

Questions;
1. How can I isolate the bad component from here?
2. Is it something with the Gate regulation of the MOS fet? See blue region.
3. I dont need any USB stuff. Could we cut the copper paths somewhere?
4. Maybe make a homemade 3.3V regulater just to feed the logic board?
(5. Buy from ebay 10$+16.75$? DELL USB BOARD 4H.L2H08.A02 boring...)

All inputs are welcome.
Regards toli0002

[selldoor]

Re: Dell 2007 fpb 2 seconds to black. Almost solved.

Try changing the voltage regulators on the usb board?

Are they all the same part number all tested? try swapping one over? Are the 4 small oblong component just above the regulator marked in the picture diodes? tested?

[toli0002]

Re: Dell 2007 fpb 2 seconds to black. Almost solved.

Selldoor
Thank you for you reply.
Good idea. The 12V regulator, yes with same part number, could be "borrowed" (don't need any 12V).
Not sure what "oblong" components you are thinking about? There are the parallell coupled shottky diodes that budm have already pointed out as a bad design?

Regards toli0002

[selldoor]

Re: Dell 2007 fpb 2 seconds to black. Almost solved.

Yes - probably are the shottky diodes did you test them?

[toli0002]

Re: Dell 2007 fpb 2 seconds to black. Almost solved.

Selldoor
Not tested yet. Will as soon as an time window appear!
/toli0002

[toli0002]

Re: Dell 2007 fpb 2 seconds to black. Almost solved.

Ok Selldoor

Changed Shottkys and MOS
No solution yet. But I have replaced the two Shottky diodes and the MOS fet for the 3.3V. Result, still zero voltage out. I also killed the original MOS in the progress.

Questions
Could it be something wrong with the governing of the MOS fet?
What are the components before the Gate of the MOS?
How can i test them?
It feels like we have narrowed it down quite significant. How many components are there that can have an influence on the 3.3 voltage?

New images with measurements attached.

All inputs are most welcome
Regards toli0002

[toli0002]

Re: Dell 2007 fpb 2 seconds to black. Almost solved.

Progress!
Seems to be a missing PWM out from a TL1451 controller.

Knowledge input needed
Comparing the pin status between the good and bad USB-boards shows:
pin1 CT Waveform both on good and the bad.
pin2 RT 0.9V good and 1.0V on the bad board
pin3 IN+ 1.2V good and 0V on the bad board
pin4 IN- 1.2V both boards
pin5 FEEDBACK 1.9V good and 0.8V on the bad board
pin6 DTC 0.9V good and 0V on the bad board
pin7 OUT PWM-wave good and 0V on the bad board
pin8 GND 0V both boards

pin9 to 16 look almost the same.

Please look at the attached oscilloscope images

Ideas on how to continue from here is most appreciated!
We are getting closer and closer...

Best regards toli0002

[toli0002]

Re: Dell 2007 fpb 2 seconds to black. Almost solved.

"Dead Time Control" dead?
Measurements gives pin6 DTC 0.9V on the good USB board and 0V on the bad board. With 0V on DTC the controller has to make "permanent" dead time, output always zero.
It seems like TL5001 PWM controller is a half TL1451. Then reading "Examples of Applications with the Pulse Width Modulator TL5001" (se attached pdf) tells me that there should be a current from DTC pin (pin6 TL1451). Desoldered and angled the pin 6 to measure the current gave zero current to ground.
Question
Is this telling us that the tl1451 controller is dead?
Or have I got it wrong somehow? On the Circuit Description of the TL5001 there is clearly a current driver (marked with a blue circle on the attached image).
It is tough to replace the tl1451 chip and I can not be sure that the one I put in (used) works either.
Can the tl1451 be tested in circuit somehow?

Any ideas would be most apreciated!
Regards a tired toli0002....

[leapius]

Re: Dell 2007 fpb 2 seconds to black. Almost solved.

This is probably no help at all but I have a number of working 2007fps and I think they will not work at all if the USB board is faulty or disconnected.

[toli0002]

Re: Dell 2007 fpb 2 seconds to black. Almost solved.

Hi Leapius!

Thank you for your reply.
Yes you are right. The USB-board feeds the Logic-board with 3.3V. The pwm controller tl1451 that I am fighting with is supposed to make the 3.3V. I have seriously thought about replacing the USB-board with a new switch regulator only for the 3.3V.

Thanks again for your feedback. Started to get tired to talk to myself.

Regards toli0002

[leapius]

Re: Dell 2007 fpb 2 seconds to black. Almost solved.

No, I know man it sucks I just wish I could help bring it back to life for you.. Sounds like you're pretty far down the rabbit hole with this one. Am I right in thinking you have a working USB board from another screen and then it works ok? Maybe try feeding it 3.3v from external supply to test? Don't give up, you'll get there!

[toli0002]

Re: Dell 2007 fpb 2 seconds to black. Almost solved.

Idea
Get rid of the whole USB-board and replace it with a simple 19V to 3.3V down converter
Result
Did not work either! Applying an external 3.3V source directly to the Logic-boards pin 8 on the connector (see attached pic) was like a short. Now I got worried that I fried the Logic-board! Quickly back with the ok USB-board and.... . Still working, the now extra beautiful DELL-logo started slowly and gracefully to move over the screen.

Conclusion

1. Just throwing away the USB-board and replacing it with a simple 3.3 step down converter is not a straight forward approach. Sigh.
2. Guess it is easier (less hard) to just fix the USB-board.

Maybe it is time to swap the possible bad 3.3V tl1451 with the tl1451 for external speakers 12V connector?! What do you think?
There is a risk that I mess up the circuit board just to realize that it probably where a tiny resistor or cap that was bad instead.

Your input feels more valuable then ever right now.

Thanks in advance
Yours tl0002

[selldoor]

Re: Dell 2007 fpb 2 seconds to black. Almost solved.

Hi - I have been away for a week - back on the case now - trouble is I dont know that much about circuits. (or anything much really) Budm is the man.

I have been thinking perhaps the small switching transistors are kaput.
This is the sheet for one of them ZA


I will look for the other.

Here 1AM

[toli0002]

Re: Dell 2007 fpb 2 seconds to black. Almost solved.

Hi all

Dell 2007fpb dead is now SOLVED!

Thank you Selldoor for the transistor info! You got me on the right track. There was nothing wrong with the transistors though. But the 2.7K resistor between the tl1451 and the first transistor had died! It's under the white glue. This finding feels so good! What could be the reason of the resistor death? Any ideas?

One USB-boards repaired so far and next is up for a treatment.

Regards toli0002