DELL 2007FPB - black screen - power diode is green - backlight is purple/amber :)

[budm]

Re: DELL 2007FPB - black screen - power diode is green - backlight is purple/amber

One of the pin should have at least 3.3v for input to get 1.8V output. The top pin is the input pin VCC.
That switching power supply (the round inductor L2) that supplying the VCC is not working.
What DC voltage do you get at F1 fuse, it should be 5 or 12v at both ends of the fuse, black probe on the chassis.
This board has two switching regulators driven by IC US1.
Check voltage at 'VLCD' pad by L1 also.

[retiredcaps]

Re: DELL 2007FPB - black screen - power diode is green - backlight is purple/amber

It should show me 1.8V not those small measures ?

Yes, it should be 1.8V output. I marked up another diagram.

1) There are 3 points to measure. VCC18, VCC, and VIN. Put your black probe on a ground screw or chassis and measure the DC voltage of the three. Put your red probe on each circled point. Report your findings.

2) F1 is a fuse. Measure the voltage on each side of the fuse with respect to ground. You should have 2 readings.

edit: Beat by budm again while I was doodling in paint.

[madfreak]

Re: DELL 2007FPB - black screen - power diode is green - backlight is purple/amber

So i guess i have to replace it, ok , i just have to search for it, it will not be easy but not as hard either. One thing that i have to buy also will be hot air, because without it i will not replace that voltage regulator.

Thank You for Your kindness. And possibly in few days i will got all stuff, the hot air gun and that chip .

Regards

Thomas

[retiredcaps]

Re: DELL 2007FPB - black screen - power diode is green - backlight is purple/amber

So i guess i have to replace it, ok

Don't replace it yet. Answer posts #21 and #22 first.

[budm]

Re: DELL 2007FPB - black screen - power diode is green - backlight is purple/amber

No, it does not mean it is bad since the VCC is way too low to feed that regulator as I indicate, you need to take the voltage reading at the TEST PAD VCC first and at the fuse also.

[madfreak]

Re: DELL 2007FPB - black screen - power diode is green - backlight is purple/amber

VCC - 0.83V - 0.84V

VCC18 - 0.67V - 0.68V

VIN - 18.36V - 18.37V

FUSE on both sides - 18.37V - 18.38V

VLCD - 0.50v - 0.51v

[budm]

Re: DELL 2007FPB - black screen - power diode is green - backlight is purple/amber

Regulator is not the problem. How about the voltage at VLCD pad?

[madfreak]

Re: DELL 2007FPB - black screen - power diode is green - backlight is purple/amber

VLCD - 0.50v - 0.51v

[retiredcaps]

Re: DELL 2007FPB - black screen - power diode is green - backlight is purple/amber

What is part number US1?

[budm]

Re: DELL 2007FPB - black screen - power diode is green - backlight is purple/amber

I am going to bed now, but retiredcaps can tell you how to check those MLCC for shorts, that will be the next step. Also look up the spec of that switching IC US1 to see the pinouts. Good night!

[madfreak]

Re: DELL 2007FPB - black screen - power diode is green - backlight is purple/amber

Good night and thank You really much . Have a sweet dreams

[madfreak]

Re: DELL 2007FPB - black screen - power diode is green - backlight is purple/amber

US1 - ( from top to bottom lines )54383 89TG4 C2RE

[retiredcaps]

Re: DELL 2007FPB - black screen - power diode is green - backlight is purple/amber

I am going to bed now, but retiredcaps can tell you how to check those MLCC for shorts, that will be the next step. Also look up the spec of that switching IC US1 to see the pinouts. Good night!

I'm calling it quits too and I'm hour before ahead of budm in SF.

For your homework, find the datasheet for US1 and see if VCC is shorted to GND. Post the URL here so I don't have to look it up.

For a shorted MLCC, see my case study at

https://www.badcaps.net/forum/showthread.php?p=114994

[madfreak]

Re: DELL 2007FPB - black screen - power diode is green - backlight is purple/amber

Ok, i am really grateful for Your help , there are such, a great peoples living on earth . I am starting to search for that chip ( it has "i" logo, so maybe it is INFINEON ). When i found it i will post, a link to datasheet.

Many thanks

Regards

Thomas

[madfreak]

Re: DELL 2007FPB - black screen - power diode is green - backlight is purple/amber

Ok, after some quick research i have found something similar to that chip
( i think that is the same part but different manufacturer ) :

https://cdn.badcaps-static.com/pdfs/...674975cef2.pdf

And after measurments, that chip do not have shorted PINS ( 4 (GND) + 1 (PVDD1), 4 (GND) + 14(PVDD2) )

[madfreak]

Re: DELL 2007FPB - black screen - power diode is green - backlight is purple/amber

US1 - ( from top to bottom lines )54383 89TG4 C2RE. i just realize that this is exactly TEXAS INSTRUMENTS, because of logo in that datasheet , it is exaclty as it is on that chip . And maybe i am searching in the wrong way by "googling" it but that is the only datasheet that i was able to find over the web.

[retiredcaps]

Re: DELL 2007FPB - black screen - power diode is green - backlight is purple/amber

And after measurments, that chip do not have shorted PINS ( 4 (GND) + 1 (PVDD1), 4 (GND) + 14(PVDD2) )

1) So what are the DC voltage measurements on all the pins with respect to ground? You can use a ground screw on the board for your black probe.

2) Have you checked all the ceramic caps for shorts yet?

[madfreak]

Re: DELL 2007FPB - black screen - power diode is green - backlight is purple/amber

Ok, now that chip is dead i guess... . I measure all the pins, and after cominng to last few, i shorten pins, i got to weak eyesight to do that kind of measurments on that small components .

Possibly, that chip was good, and there is a shorten smd capacitor or some small cheap part, but now that chip shows almost on every pin 0V.

Before my "shaking hands" :

i got :

1 PIN - 18,37V
2 PIN - 5,75V
3 PIN - 0,20V - 0,73V ( IT DROPS AND GOES UP THAT VOLTAGE )
4 PIN - 0V
5 PIN - 0,18V
6 PIN - 0V
7 PIN - 0,04V
14 PIN - 18,37V

But now they are all almost 0V, so i damagaed that chip i guess, and i have to wait when i will bought it

[madfreak]

Re: DELL 2007FPB - black screen - power diode is green - backlight is purple/amber

Yes, now it shows on PIN 1 and PIN 14 0,03V so i guess i am so dumb that i damaged something that was good . Ok now i will have to find out where i will bought that chip, it will not be easy task .

Take care You all, and thank You for help, but i guess i will throw it to the trash, because i will not find that chip soon .

[madfreak]

Re: DELL 2007FPB - black screen - power diode is green - backlight is purple/amber

So now, if someone could help me to find that chip i will be grateful :

54383 89TG4 C2RE