Dell 2007WFP Won't Power On

[alexanna]

Re: Dell 2007WFP Won't Power On

Is F19 good on the USB board?

[alexanna]

Re: Dell 2007WFP Won't Power On

I have a 2007 WFP that I am going to be working on today, the only problem it has is with one of the back lights. Initially when I was testing this on the bench I neglected to have the USB board attached, and of course the monitor would not work, so like pedro and PlainBill state it plays an important role in generating the other voltages.
If you need to know what any of the good pin or component voltages on the USB board are let me know.

[PlainBill]

Re: Dell 2007WFP Won't Power On

The USB board obviously produces a regulated +5V from the 19V supply. Is it a possibility that THAT is the supply for the logic board, and NOT the 19V? If they are going to use 3-terminal linear regs for 3.3v etc on the logic board, that would make sense.

I'm sure it is. There appear to be four bucking regulators on the USB card. This is definitely an older design; I came across something similar on a Viewsonic VP211B; on that monitor the power supply put out about 18Vdc; the bucking regulators and the USB hardware were on the signal card.

PlainBill

[pedro]

Re: Dell 2007WFP Won't Power On

The USB board obviously produces a regulated +5V from the 19V supply. Is it a possibility that THAT is the supply for the logic board, and NOT the 19V? If they are going to use 3-terminal linear regs for 3.3v etc on the logic board, that would make sense.

[PlainBill]

Re: Dell 2007WFP Won't Power On

I've been pouring over the pictures for the last 15 minutes, getting more frustrated by the minute. First of all, if you have 19 volts on the USB card, the power supply is working.

Next, what are the voltages on each of the 12 pins connecting the signal card to the USB card?

There are 4 regulators you have indicated have 19V on two pins. What are the part numbers of those 4 ICs?

Last, what is the part number of U2 on the USB card. What is the voltage on the three pins?

PlainBill

[retiredcaps]

Re: Dell 2007WFP Won't Power On

Hmm. Something is nagging me about this USB board. I seem to recall PlainBill saying something about being a DC-DC converter. Let me search around to see if I can find it.

[retiredcaps]

Re: Dell 2007WFP Won't Power On

On one yet to be solved monitor, whenever I hooked up the logic card, my power supply went from 12V DC to 0V DC.

I wonder if the USB board is shorting out the logic board? Try removing the USB board and re-measuring the logic board for DC voltages?

Of course, my monitor is dead so I can't even measure voltages. Looking at the power board, there is only one 470uF 35V cap which leads me to think that 19V DC is the only secondary voltage provided?

[croket]

Re: Dell 2007WFP Won't Power On

I just traced the circuit on the board for those 2 wires (brown and Black) coming into the logic board that read 19v. They go directly to the connector that connect to the USB board.
they don't energize the logic board at all. I've tested several other components on the logic board they they all read 0v, the entire board has no voltage. The usb board however is a hole slew of components reading 19v.

This leads me to believe that there has to be another wire that energizes the logic board, however there isn't. take a look at the USB board. its hot. the logic is dead.

[retiredcaps]

Re: Dell 2007WFP Won't Power On

Just did it, I got 0v on all legs both chips

Other than replacing the voltage regulators, I can only think of the caps on the logic board being user replaceable. Everything else is too small or too complicated or proprietary to replace.

Maybe a cap is bad on the logic board?

[croket]

Re: Dell 2007WFP Won't Power On

Just did it, I got 0v on all legs both chips

[retiredcaps]

Re: Dell 2007WFP Won't Power On

I re-tested U13 and U5. This time I placed the red probe from the DMM on the black wire coming into the board showing 19v, With the black probe I touched every leg on both chips and I get 19v on my DMM indicating all the legs are grounded.

Here is how I test voltage regulators. Put your black probe on the ground screw (this is your ground) on the logic board. Put your red probe on each pin of the 3 legged voltage regulator.

Now what do you read?

[croket]

Re: Dell 2007WFP Won't Power On

I re-tested U13 and U5. This time I placed the red probe from the DMM on the black wire coming into the board showing 19v, With the black probe I touched every leg on both chips and I get 19v on my DMM indicating all the legs are grounded.

The weird thing is when I try to tone it out (continuity beep) they don't all ring out. On U13 only the left legs rings out and on U5 the middle leg rings out. I"m using one of the screw holes rings on the board for ground.

Any thoughts?

[retiredcaps]

Re: Dell 2007WFP Won't Power On

On my board, all pins on both regulators are shorted to ground.

[retiredcaps]

Re: Dell 2007WFP Won't Power On

Shouldn't I get some kind of voltage on the "in" pin on either regulator even if they are bad?

Hmm, good point.

What are you using for ground when measuring U13 and U5?

[croket]

Re: Dell 2007WFP Won't Power On

Shouldn't I get some kind of voltage on the "in" pin on either regulator even if they are bad?

[retiredcaps]

Re: Dell 2007WFP Won't Power On

No I'm not getting any voltage on any of the pins of the regulators (U13 and U5). I've got 19v on the 2 far right wires (brown & Black )at the connector above the regulators.

The fact that you are getting 19V DC on the wires shows that voltage is getting to the main board, but the voltage regulators are dead.

If you are not getting any DC voltage on U13 and U5, that would explain the lack of the power led going green. That means U13 and/or U5 are both bad. If you have junk boards laying around, you may be able to desolder an old one and use it. Or just order them from digikey or mouser.

On mine, U13 is 952T43 (a 1.8V 1A)

http://www.alldatasheet.com/view.jsp?Searchword=952T43

U5 is 950T65 (2.5V 1A)

http://www.alldatasheet.com/view.jsp?Searchword=950T65

1.8V and 2.5V DC is what you should get if the regulators are working properly.

[croket]

Re: Dell 2007WFP Won't Power On

No I'm not getting any voltage on any of the pins of the regulators (U13 and U5). I've got 19v on the 2 far right wires (brown & Black )at the connector above the regulators.

[retiredcaps]

Re: Dell 2007WFP Won't Power On

And yes you're correct, 19V is what I'm getting.

If you are getting 19V DC at CN701, that implies your power board/supply is working.

On the logic board, now measure the DC voltage each pin on both voltage regulators. Even though these regulators are not shorted (like mine), they still could be out of specification.

[croket]

Re: Dell 2007WFP Won't Power On

retiredcaps, Thanks for the compliments on the pictures, I realize how critical it is when working on an item that you don't have in front of you. I"m a big fan of close up detailed pics.
I've checked the U13 and U5 components on my board and they read ok, not shorted. Also read the the 2 diodes (FD4) on the USB board and they too were not shorted (i also checked every diode of the same Part# number as FD4) .
And yes you're correct, 19V is what I'm getting.

Rtech, I removed Schottky diode (D701) to test out of the board and it checks OK. I put it back in and plugged the board in, Both caps C711 and C713 read 19 vdc across.
I was able to read the part number off the 8 legged chip, it is 200a6, I also hunted down the datasheet for it witch I uploaded. I'm not exactly sure what to look for in that datasheet so your more than welcome to talk a look at it.

What I did find is a shorted diode on the bottom side of the power board, (D604). its to the left of the 8 leg SMPS chip (if looking at my pic). other than that I can't seem to find anything els.
Thanks for helping out guys, anything else I should be looking at?

[Rtech]

Re: Dell 2007WFP Won't Power On

The 160V on both pins of the transformer is probably correct,and one of thos normally goes to the Large Filter cap,and the other to the Mosfet on the Heatsink.Provided the SMPS chip ( the 8 legged one )next to the transformer,is functioning correctly,then this drives the Mosfet to feed the transformer. On the other side then,where you are getting 0 volts,is probably not the best place to check.D701 looks like a Schotky diode,and the rectified voltage from that,feeds C711 and C713..measure the DC voltage across the caps and check the diode by using the diode test funtion on your meter(if you have one)The latter with the power OFF.Also advise the part code of the 8 legged smps chip ?