Dell 2007FPB teardown

[knightace]

I found the Problem, I was connecting the Connector the opposite way, that is the reason why the fuse blew. (Due to Direct Short Circuiting) but Now there is another problem, I got LCD Running Perfectly, but there is no Picture. I mean that The Backlight is OK and Working but there is no Picture, like No Input, or no Signal etc.

[knightace]

Guys.. a little help would be appreciated. I have burnt power board of Dell 2007WFPB. This Board has burnt SMD resistors, the Board number is 4H.L2J02.A04. I have attached image of the board. if anyone could get me a clear picture of the board from bottom, kindly attach it with your reply, I am in a real need of the smd resistor codes on the bottom of the power board. The image for Reference has been attached with this post

[lotas]

Originally Posted by knightace

Guys.. a little help would be appreciated. I have burnt power board of Dell 2007WFPB. This Board has burnt SMD resistors, the Board number is 4H.L2J02.A04. I have attached image of the board. if anyone could get me a clear picture of the board from bottom, kindly attach it with your reply, I am in a real need of the smd resistor codes on the bottom of the power board. The image for Reference has been attached with this post

Here is a diagram that should fit

[knightace]

but its for Dell 2407 not 2007 plus I'm New in this Field . If you could really help with the area in the red Square. That area is burnt ( Resistors and A zener diode) if i could get the codes, i could replace them all. If you or anyone could arrange a Picture containing that area so that i could get smd resistor codes, I would be really really Grateful
The image of the burnt Part of PCB has been attached with this Post as well

[lotas]

So you write what serial numbers of resistors and zener diodes burned on the board, for example: R623, R613 .... and so on and I will write you the smd code of these resistors according to the scheme

[Behemot]

Me thinks the upper two which you selected are for the two components on the left side. For those two in the right side also the right two numbers apply. That would be JR2 and R613 I guess.

[lotas]

It is hard to see from the photo what else has burned out, but if these resistors burned out, then most likely Q601, IC601 and something else burned out

[knightace]

Originally Posted by lotas

So you write what serial numbers of resistors and zener diodes burned on the board, for example: R623, R613 .... and so on and I will write you the smd code of these resistors according to the scheme

I am so sorry for the image, I only shared it for Reference, Just to point out the Faulty resistors and zener diodes. I will upload full focused Image and images from different angles so that you get a clear image of the problem I have with the board. I will upload Complete set of Images of the board and the damaged part of the board with enough focus that you can clearly see the Resistor codes aswell as the Damaged Portion.

Thank you So much again for replying me.

[knightace]

Today I took the Images from Closer look of the board. The Codes are pretty Clean. There was also some kind of Fume like colour on the Solder tips of the Components attached from the Top of the board and a high watt resistor Burnt/damaged. All the Images are shared. I would also be grateful if you people could find the root of this damaged, because what i did was only using multimeter and checking voltages across ground and points on the board (With board connected to AC Mains) and suddenly

The Images with name circuit-index will give you a proper view of the circuitry of the board ( I tried to take the negative so that all black becomes white . Thought the codes would be easier to read) .

[knightace]

Originally Posted by lotas

It is hard to see from the photo what else has burned out, but if these resistors burned out, then most likely Q601, IC601 and something else burned out

You are Right that Burnt Resistor that I shared was linked with Q601 (Its a Transistor with Code 2SK3548, I'm not sure but im guessing it is used to create sine wave Electrical Signals), By the way the DC from the Transformer was above 1000V thats what my Multimeter was showing ( its max Limit is DC 1000V)

[Behemot]

If you mean main transformer secondary, there's AC coming from it, you can measure DC after rectifier, preferably on a capacitor.

What would be a sine wave doing there?

[knightace]

Its not Secondary, its Primary thats connected with the Transistor, Look I am confused here, because the Voltage that I read after being rectified into DC from 450V 180uf Cap is 328V dc. And then the Transformer shows above 1000V , How is it even possible ! . I dont know much but I will tell you what I understood about this Board. It takes 220V Mains AC , Rectifies it into DC, then converts it back to AC for the Transformer , steps down it to 19v and then rectifies it back again. If this is right what I said, then why convert it into DC if we want to step down it later , why not step down AC Directly and then Convert it into dc?

[Behemot]

That's correct, ~230 V AC times square root of 2 equals to a bout 325 V. Where would DC appear from on the transformer? Since when can transformer transform direct current? A switch (usually transistor) cuts the DC into some kind of AC wave which can only than be transformed to higher or lower voltage.

The key value here is frequency. Low-frequency transformers (like the networks 50- or 60Hz) are huge and infficient for higher power passing through them. Switched-mode power supplies work usually within the 60-100 kHz range (but generaly can operate anywhere between 10 kHz and 10 MHz).

[knightace]

Originally Posted by Behemot

That's correct, ~230 V AC times square root of 2 equals to a bout 325 V. Where would DC appear from on the transformer? Since when can transformer transform direct current? A switch (usually transistor) cuts the DC into some kind of AC wave which can only than be transformed to higher or lower voltage.

The key value here is frequency. Low-frequency transformers (like the networks 50- or 60Hz) are huge and infficient for higher power passing through them. Switched-mode power supplies work usually within the 60-100 kHz range (but generaly can operate anywhere between 10 kHz and 10 MHz).

OH!! WHAT Was I Thinking... Sorry you are right ! about That AC Coming or going to Transformer, Transformer would never work on DC either for Primary or Secondary as it works with the Inductance Phenomenon.

Still, I need the Codes for the resistors, and Zener Diodes, Furthermore if you find out any Problem with the PCB, Solder Joints, or shorts, any help would be Greatly Appreciated !

And one thing more that's been messing up my mind, I asked that in my Previous post as well, why convert it into DC if we want to step down it later , why not step down AC Directly and then Convert it into dc?

[Behemot]

Originally Posted by Behemot

The key value here is frequency. Low-frequency transformers (like the networks 50- or 60Hz) are huge and infficient for higher power passing through them. Switched-mode power supplies work usually within the 60-100 kHz range (but generaly can operate anywhere between 10 kHz and 10 MHz).

[Fr0sT]

Guys,

I have a 15 year old 2007WFP, which is has been a faithful servant until recently when it developed the notorious 2 seconds to black issue. I've taken it apart along with the panel and when powering it up one of the six CCFLs does not light up, the other 5 light up and shut down shortly so I got a faulty CCFL.

This is where I decided to try and upgrade it to LED backlight, ordered this kit:
https://www.aliexpress.com/item/3280...100a4c4dlB7ZH9

And the obvious questions - where do i get the VIN (12v ?), ON/OFF and ADJ (adjustment) points (I think ground is not that difficult). Do I get them from the main board, inverter, power board ? Logic tells me on/off and adjustment should come from main (logic board) but tracing the connections they should pass through the power board and go to the inverter, does that make any sense ?

Any help is appreciated.

[Behemot]

That's usually the case. If the pins are not labeled, you can always find datasheet for the inverter driver and have a look which pins are what.

[Fr0sT]

OK I think I got the pins I needed on the power board on the connector towards the inverter (marked on the first picture). I've tapped directly on the connections from the power board towards the inverter and left the inverter board disconnected, just connected the LED driver board on it's place. All went good, the 2 LED strips lighted up when hitting the power button, I've assembled back the panel and tested it again - the "No input signal" box appeared on the screen, jumping up and down. At this point I wanted to test the brightness adjustment before final assembly and hooked the monitor to my PC but unfortunately somehow I've shorted the power board and all went out with sparks, smoke...

At first look the big capacitor seemed fried (marked in orange on the first picture), measuring it's pins with my multimeter results in 0 resistance, it also beeps on shorted circuit.

First question is can I replace it with any other 180uf 450V capacitor, I've found some in local retailers but smaller in size and temperature (85C vs 105C).

Second question is is it possible that I've fried something else besides that capacitor, any ideas what to check ?

Apologies if questions seem silly but I'm more of a computer guy and electronics has never been my strong field, still I'd want to fix that monitor.

[Behemot]

Capacitor does not seem to have any problem, you've just discharged it via short. If it was plugged in the grid during that, than surely fuse and the bridge rectifier BD601 went out if you measure it shorted. Take it out and take measurement again to see whether also the switch or controller are fried, or just the rectifier itself.

[Fr0sT]

Yes, I shorted it while connected to the grid

Anyway I've taken the capacitor off the board and now there is no resistance, it's not shorted so I guess it's ok.

Bridge rectifier BD601 - each pin is shorted with each pin (measured it while removed off the board), + and - pins have some burnout on them (see attached pic) so I guess it's dead ?

Fuse F601 - measured it taken off the board and it's open circuit so it's also dead.

Which are the switch and controller elements ?