DELL 1907 FPT power supply

[Jack S]

I have a DELL 1907 LCD monitor that powers on only for a few seconds then the backlight turns off but the power button stays green.
There are no physical signs that the caps are bad.
I removed the lamps and replaced them with known good ones and the problem still exists.
Any help would be appreciated.

[PlainBill]

Re: DELL 1907 FPT power supply

I have a DELL 1907 LCD monitor that powers on only for a few seconds then the backlight turns off but the power button stays green.
There are no physical signs that the caps are bad.
I removed the lamps and replaced them with known good ones and the problem still exists.
Any help would be appreciated.

You have two problems. The first is minor, and not worth worrying about - you posted in the power supply section, rather than the computer display section.

The second problem is you have a bad inverter. The first step is to resolder all the pins on the transformers. Dells are notorious for cracks where the transformer pins are soldered to the board.

Also, post good quality pictures of the top and bottom of the board.

PlainBill

[Jack S]

Re: DELL 1907 FPT power supply

Thanks. I will resolder the pins on the transformer and put my messages in the proper location.

[Bobdee]

Re: DELL 1907 FPT power supply

Thanks. I will resolder the pins on the transformer and put my messages in the proper location.

It is in the right place now

[alexanna]

Re: DELL 1907 FPT power supply

I wondering if we could start this thred up again.
My Dell 1907 is showing a good green light when video siginal is present,But no back light activity at all.The discoloration on back of board is because of lighting.I have resolderd the two coils for back lamps. The ic chips 8 pin near
the two coils is a # bd6t18. also, This board looks just like the one they use in the 1707fpt. I have used known good lamps for testing

[jsaily]

Re: DELL 1907 FPT power supply

I wondering if we could start this thred up again.
My Dell 1907 is showing a good green light when video siginal is present,But no back light activity at all.The discoloration on back of board is because of lighting.I have resolderd the two coils for back lamps. The ic chips 8 pin near
the two coils is a # bd6t18. also, This board looks just like the one they use in the 1707fpt. I have used known good lamps for testing

Hi! I have exactly the same board here with similar symptoms. It's from a Dell 1707fpt I rescued from the dumpster recently I checked all power supply and logic board caps with an ESR meter and didn't find anything too suspicious, all were 0.1-0.3 ohms. I replaced all the inverter caps anyway but there was no change. Next I'll have to try with good lamps from another monitor I rescued (Acer AL1716A, has problems with VGA syncing but steady backlight ).

Is there a schematic of the inverter on these Dell boards? There are a lot of tiny SMD transistors which are hard to identify.

-- Jussi

[jsaily]

Re: DELL 1907 FPT power supply

Hi! I have exactly the same board here with similar symptoms. It's from a Dell 1707fpt I rescued from the dumpster recently I checked all power supply and logic board caps with an ESR meter and didn't find anything too suspicious, all were 0.1-0.3 ohms. I replaced all the inverter caps anyway but there was no change. Next I'll have to try with good lamps from another monitor I rescued (Acer AL1716A, has problems with VGA syncing but steady backlight ).

Is there a schematic of the inverter on these Dell boards? There are a lot of tiny SMD transistors which are hard to identify.

-- Jussi

I would like to add that there is an audible 'white' noise which seems to come from one corner of the LCD panel when the monitor is turned on. I tried to localize it and it doesn't seem to come from the power supply/inverter board. The sound ends when the backlight is switched off in about 2 seconds after powerup.

Is it possible for the CCFL tubes to emit noise? I'll try to switch the inverters and backlights from the Acer monitor mentioned above tonight, and see where the real culprit is...

-- Jussi

[alexanna]

Re: DELL 1907 FPT power supply

I will try to answer this,Iam not sure what a white noise is? But I guess any thing is possible.What I have found on several monitors is burned/poor solder joints on the two upper return lines of the ccfls.Do try known good lamps to rule that out.
Your problem is not the same as i am having.
Good luck.

[alexanna]

Re: DELL 1907 FPT power supply

Well when I start thinking about things I realy don't about I can get myself in a lot of trouble, But here goes is the ic bd6t18 a driver for the back lamp ckt. I can not find a data sheet on it?

[PlainBill]

Re: DELL 1907 FPT power supply

jsaily, the 'white noise' sounds like arcing at one of the CCFLs. This can be due to a bad solder joint, or bad insulation on the wire.

Alexanna, your problem is a lot harder to identify. It could be anything from a problem on the logic card to a bad solder joint in the inverter. Other suspects include no power to the inverter, and shorted (or open) transistors.

The biggest problem is going to be identifying components. Related to that is the pictures just aren't clear enough to be really useful.

Let's try a slightly different approach first.

On the bottom of the board in the inverter area is an 8 pin IC, either I101 or IC01. What is the part number of that IC?

In the lower right hand corner of the top view is the multi-conductor cable running to the logic card. Is there any legend identifying the function of the pins?

The two 'ICs' by the transformers appear to be transistor arrays (identifier starts with Q). Please write down the information printed on them exactly as it appears. I suspect BD6T18 includes a date or production code.

Have you tried to see if there is any image present on the monitor while the power led is green? Sometimes a flashlight helps.

OH!! And do you have access to a better camera?

PlainBill

[jsaily]

Re: DELL 1907 FPT power supply

jsaily, the 'white noise' sounds like arcing at one of the CCFLs. This can be due to a bad solder joint, or bad insulation on the wire.

Thanks for the tip! I'll try to move the wires a bit and see if there is any change to the noise. Can you suggest an easy/safe way to resolder the CCFL wires? I've got no prior experience on dismantling LCDs, but am willing to take the risk in this case Also, is it safe to test the inverter without all tubes connected, like one at a time? If the safety circuit kicks in without a load then it doesn't work...

By the way, I read the inverter driver chip to be BD6D24 or BD6D2H with a production code P607. It's really hard to be sure. The SO8-sized chips on the under side have markings which need a magnifier to be read, I don't have one at home but maybe I can bring the board to work tomorrow and check them out.

The discrete TO92-sized transistors around the inverter are 2N7000 (N-ch MOSFET), 2SC945 (NPN) and 2SA733 (PNP). There are a few surface mount transistors on the underside the markings of which are hard to read.

-- Jussi

[alexanna]

Re: DELL 1907 FPT power supply

Jsaily,
The cfls are not that bad to repair.The biggest problem I have had is dust getting below the lcd.You will need very small screwdrivers and a good memory as how things go together.As I dissasemble I keep every thing together in the order they come apart.Alter you remove the lcd. and all the difusers you will be left with the frame and a thick peice of plastic.Carefuly remove the plasitc leaving the frame and ccfl housing.Be careful with the silicone insulators thet can rip eaisly I have used wd40 to get them moving.There has been enough wire for me to fish enough wire down the housing to resolder.keep your solder joint as small as possible,If it is to big you will increase the length and you will have troubles with reassmbly.Make sure every thing is insulated with no bare wires.Also I am told the yellow kapton tape is a must for heat . My lcd is dissambled at this time I will answer Plain Bills questions as soon as i can.

[alexanna]

Re: DELL 1907 FPT power supply

I think I have some better pictures. The multi colored wiring from the psu. To the video board has no identifiers. The monitor is apart at this time so I do not know if a image appears w/flashlight. If I could identify which wire was commanding the bl. On I could at least know if the video board was asking for b.l. The power led dose go from solid green when video is hooked up to solid amber when vga is disconnected. If needed I ill reassemble to check image w/ flashlight

[PlainBill]

Re: DELL 1907 FPT power supply

I think I have some better pictures. The multi colored wiring from the psu. To the video board has no identifiers. The monitor is apart at this time so I do not know if a image appears w/flashlight. If I could identify which wire was commanding the bl. On I could at least know if the video board was asking for b.l. The power led dose go from solid green when video is hooked up to solid amber when vga is disconnected. If needed I ill reassemble to check image w/ flashlight

More Paint!!! I've identified the two lines that control brightness and turn the CCFLs on and off. See attached picture.

The inverter controller is an OZ9936. The manufacturer's site is here. For some reason they don't have datasheets available.

I'm trying to identify the manufacturer of the inverter drivers. What is frustrating is I have seen the logo. It does not appear to be Advanced Power Electronics Corp, although the logos are similar.

PlainBill

[alexanna]

Re: DELL 1907 FPT power supply

On the bottom pin, reads 2.5v monitor on and 3.3v off.
pin 2nd from end is 3.3v on w/green light and 0v monitor off.And yes Iimmage appears on screen w/ flashlight. Its looking like this might be fun,I havent been able to find any data on these 2 items also.
Thanks Al.

[PlainBill]

Re: DELL 1907 FPT power supply

On the bottom pin, reads 2.5v monitor on and 3.3v off.
pin 2nd from end is 3.3v on w/green light and 0v monitor off.And yes Iimmage appears on screen w/ flashlight. Its looking like this might be fun,I havent been able to find any data on these 2 items also.
Thanks Al.

As an exercise for the student, locate the inverter power line and check the voltage on it.

For extra credit, trace the two lines above and see if their are any dead semiconductors in the path.

PlainBill

[alexanna]

Re: DELL 1907 FPT power supply

As an exercise for the student, locate the inverter power line and check the voltage on it.

For extra credit, trace the two lines above and see if their are any dead semiconductors in the path.

PlainBill

I am not quite sure what you are asking me to check? when you say inverter power line do you mean the line to ccfl connector? and I also am unsure of what two lines you are wanting me to check?

[PlainBill]

Re: DELL 1907 FPT power supply

I am not quite sure what you are asking me to check? when you say inverter power line do you mean the line to ccfl connector? and I also am unsure of what two lines you are wanting me to check?

Let's see if I can make myself clear. The power supply and inverter are on the same board, but there are often only two conductors connecting them - Inverter power and ground. (This one seems to have four - possibly multiple traces). The bottom two pins on that connector carry the brightness and On/Off control signals from the logic card.

Why won't an inverter work, even for a brief second? In detail, there are many reasons, but some are easy to check. Let's list a few:

1 No power from the power supply (typically 12 volts, could be higher).
2 No 'On' signal from the logic card.
3 Brightness set too low (again, from the logic card).
4 Defective inverter controller
5 Defective drivers
6 defective transformers
7 On/Off signal not getting to the inverter controller
8 Brightness signal not getting to the inverter controller.

You have already found that 2 and 3 are not the case, but those control signals often go through one or more transistors and resistors. Tracing those lines in a picture is a royal pain in the anatomy; it's only slightly easier if you have the board in hand.

The power is a different matter. Most designs provide power to the inverter whenever the power supply is plugged in. There are two ways to identify the actual traces. At this point you can stop reading and see if you can figure them out.

But I've lead you on the path to enlightenment (that really sounds like I'm full of it) long enough.

Clue 1. Power supply traces are much heavier than signal lines. Ground is easy to identify - somewhere or the other it goes to the pads surrounding one or more of the mounting holes.

Clue 2. Large electrolytic caps (typically 220uF - 1000uF) are used to filter the power supply. Where do we see those? Well, we see two clusters of them in the area of the heat sinks. And we see six of them in the inverter.

So here is your homework. Be careful - voltages up to 160 VDC are present on the power supply!!!

1. With the power unplugged, verify that the - pin of the electrolytic caps in the inverter area actually go to ground.

2. Plug in the power and measure the voltage across those caps. If one or more are at 12 - 24 volts, we know the power supply is working, and the inverter is getting power.

3. Trace the two lines from the logic card as they go to the inverter controller. Make sure they change state as you hit the power button. IF for example the line that goes from 0 to 3.3 volts goes to a transistor, but neither of the other two leads of the transistor change voltage when the button is pushed, you probably have found the problem.

PlainBill

[ecking767]

Re: DELL 1907 FPT power supply

hope this help. the output MOSFET are P609 OR AOP609 manufactured by Alpha & Omega Semiconductor

[alexanna]

Re: DELL 1907 FPT power supply

Plain bill,
Wow. That's a very good explanation but I think it made my headache a little worse.
Now it's my turn to be serious. thank you that is a very good explanation ,what I am going to have to do is get my head ,eyes and hands all in sync, And I will Report back later. Thanks.

Ecking767,
Thank You for The data sheet.
Al.
I have also have what I beleave to be a better pitcure of back of board