Firstly about safety. This monitor has lethal voltage inside. Especially on the the large cap and associated circuit sections on the L shaped power supply board.
Stage one of the power supply rectifies 115 Vrms houshold AC and feeds it into the 180 uF 450 V cap. Just two torroidal inductors and maybe a transformer limit the current. This cap holds a lot of energy and has the power cord feeding more energy in as well. This part of the circuit is designed to provide very high current spikes to the rest of the power supply without having much droppout in voltage. If you touch it, it will provide a very high current spike to your body almost like a defibrillator would.
Additionally, a possibly design flaw is that this cap charges up as soon as the power cord is plugged in. The power supply has no soft off function from the buttons on the front. This means that the cap is working as long as the display has AC power and could be running your electric bill up for that matter (especially if the cap starts to leak like mine)
The invertor board (which connects to the backlights) has even higher voltages than the power supply but the amount of current there MAY make it less of a threat than the power supply.
~~~
I would definately refer to another good thread about this one called "Dell 2007FPB teardown" by budm. This was very helpful to me.
I apologize I put it all back together and didn't write down the reference designators of components or take pictures. But I will provide good enough location descriptions instead.
I have fixed my monitor. I just thought I would pay it forward and let you know the cause, since this site helped me fix it.
The problem was a partially shorted reservoir cap on the power supply. This is the great big one on the power supply board mentioned in the safety section. I think its value was 180 uF and 450 V electrolytic.
Visual inspection showed a small blob of dried brown goo (electrolyte) that had oozed out the hole for the positive lead on that cap. So upon visual inspection I suspected it might be the problem but could not tell until it was removed from the circuit. I replaced it with a 68 uF 400 V electrolytic. The voltage rating is sufficient for its place in the circuit but the higher the rating the longer it lasts. So overrating never hurts with electrolytics. 68 uF made the monitor work again because it was all I had on hand. It might reduce the efficiency (below nominal) or something. But I know for sure it is more efficient than it was before with a short in it for who knows how long before it finally stopped functioning.
A cat had also urinated on this monitor. There was some kind of caustic substance all over the back of the invertor, power supply and logic boards. The power supply board also appeared to have either arc landings (little lightning strikes) all over the copper side of the board or corrosion from a substance that ate right through the green coating to the copper and corroded it as well. Like a bunch of tiny little specs and some of them in little lines and patterns.
Since this mess was on the copper side and the cap was on the component side so my guess is that the mess came from the cat and not the cap popping.
Anyway I noticed the mess before the cap so I scrubbed, rinsed, dripped, dabbed it several times with rubbing alcohol and toilet paper until upon drying there was no white haze.
The cleaning didn't fixed my problem so it wasn't until after that that I noticed the cap.
Before replacement I noticed that the voltage on the bad cap was only about 100 V. Even with the monitor in the soft off state. This is definitely a little low given straight rectification of household AC. Obviously it wasn't a dead short though.
Replacing the cap with the 68 uF fixed the monitor fully.
~~~
To be more helpful I'll describe its behavior and other stuff I noticed.
Brightness Adjust:
I had recently turned up the brightness from about 33 to 66.
Erroreous Shut Down:
When I turned it on the day it failed, the backlight would turn on but would be visibly flickering. Then after a short delay, maybe 2 seconds, it would power itself back down. I could power it up again with the button but it would keep doing the same thing.
Noisy:
Various different components on the invertor and power supply board were making various noises. The noises only occured while the backlights were still on. I probed the noise sources with a long DRY CARDBOARD tube with which I could almost isolate to the individual component.
The loudest was on the power supply board in the area between the first yellow transformer and the two little toroids (closest to the AC plug). This was kind of like a crackly buzz. I associate the two toroids are fed in series to the transformer and by some manor or another that circuit drives a full wave rectifier to charge the great big 180 uF 450 V cap. With the cap shorted I attribute the buzz to excessive current in the toroids and possibly the transformer and possibly saturation of the core as well.
There was also a seperate crackly buzz coming from the later stage transformer but it was weaker. I didn't trace out electrical connections but I am guessing this was some kind of swicther and the buzz was due again to excessive current but this time due to insufficient reservoir (input voltage) requiring longer and heavier switch cycles.
There was also a weak crackling noise coming from the large black magnetic components on the inverter board. This probably had something to do with power supply noise, low voltage, or periodic dropout.
The power delivered from the power supply was about 18.5 V when on and 18.8 V when off. This fooled me for a bit to think the power supply part was working but it wasn't fully working.
Unfortunately I didn't measure voltages once it was working. I was just happy it worked.
Once I replaced the big cap, the backlight came on perfectly and stayed on, and any noise was virtually gone.
~~~
I'll reveal that I had this monitor nearly completely disassembled before figuring out the real problem.
It was pretty easy to do. You just want to be very gentle with the LCD and the circuit film leaves attached to it. Also try to keep anything between the back side of the LCD and the front side of the 1 cm thick diffuser very clean because any debris that gets in there I am pretty sure will show up in the picture forever or at least until you open everything up again to get it out.
There are two CCFL modules. One at top and bottom. Each are about 16.75" long. Each have three CCFL tubes slightly larger dia. than a pencil lead. But remove your own and get exact form factor before buying some . . .
All six tubes worked in mine, yet there were some dark specs at the end of a few when off. Usually any kind of dark spots would seem to mean bad but in this case they might be the mercury that is in them condensed when they turn off which would be normal. That is a guess. Or it could be signs of aging, but they still work just fine.
It would be pretty easy to retrofit with LED backlights.
As budm pointed out you will still need a 19V power supply to deliver to the buck boost/USB board which will then derive power for the logic board.
You might replace the existing power supply entirely or you might leave that and re-purpose the provided 19V out to drive and LED driver. The invertor would definitely be eliminated.
In addition to the 19 V from the power supply to the invertor, there were three signals shared by the logic board. These I think are the brightness control and possibly brightness feedback. I don't know which one is which though.
You would need to determine how to translate these signals for the LED driver to maintain the ability to control brightness from the 2007FPb on screen menu.
Another pointer is that I was able to run this without the LCD component connected. Removing that from the system (and from the work area) is a good Idea while diagnosing problems that aren't related to it. Simply because it is delicate and clunky.
One final thing, this monitor uses a little bit of power, not sure how much, just by being plugged in. You might want to install a switch so it can be switched off a shoulder height or plug it into an external power strip that you can kick off with your foot to save power, and save working life of the display as well.
Good luck. Hope this helps you fix your nice display.
Be SAFE!
Stage one of the power supply rectifies 115 Vrms houshold AC and feeds it into the 180 uF 450 V cap. Just two torroidal inductors and maybe a transformer limit the current. This cap holds a lot of energy and has the power cord feeding more energy in as well. This part of the circuit is designed to provide very high current spikes to the rest of the power supply without having much droppout in voltage. If you touch it, it will provide a very high current spike to your body almost like a defibrillator would.
Additionally, a possibly design flaw is that this cap charges up as soon as the power cord is plugged in. The power supply has no soft off function from the buttons on the front. This means that the cap is working as long as the display has AC power and could be running your electric bill up for that matter (especially if the cap starts to leak like mine)
The invertor board (which connects to the backlights) has even higher voltages than the power supply but the amount of current there MAY make it less of a threat than the power supply.
~~~
I would definately refer to another good thread about this one called "Dell 2007FPB teardown" by budm. This was very helpful to me.
I apologize I put it all back together and didn't write down the reference designators of components or take pictures. But I will provide good enough location descriptions instead.
I have fixed my monitor. I just thought I would pay it forward and let you know the cause, since this site helped me fix it.
The problem was a partially shorted reservoir cap on the power supply. This is the great big one on the power supply board mentioned in the safety section. I think its value was 180 uF and 450 V electrolytic.
Visual inspection showed a small blob of dried brown goo (electrolyte) that had oozed out the hole for the positive lead on that cap. So upon visual inspection I suspected it might be the problem but could not tell until it was removed from the circuit. I replaced it with a 68 uF 400 V electrolytic. The voltage rating is sufficient for its place in the circuit but the higher the rating the longer it lasts. So overrating never hurts with electrolytics. 68 uF made the monitor work again because it was all I had on hand. It might reduce the efficiency (below nominal) or something. But I know for sure it is more efficient than it was before with a short in it for who knows how long before it finally stopped functioning.
A cat had also urinated on this monitor. There was some kind of caustic substance all over the back of the invertor, power supply and logic boards. The power supply board also appeared to have either arc landings (little lightning strikes) all over the copper side of the board or corrosion from a substance that ate right through the green coating to the copper and corroded it as well. Like a bunch of tiny little specs and some of them in little lines and patterns.
Since this mess was on the copper side and the cap was on the component side so my guess is that the mess came from the cat and not the cap popping.
Anyway I noticed the mess before the cap so I scrubbed, rinsed, dripped, dabbed it several times with rubbing alcohol and toilet paper until upon drying there was no white haze.
The cleaning didn't fixed my problem so it wasn't until after that that I noticed the cap.
Before replacement I noticed that the voltage on the bad cap was only about 100 V. Even with the monitor in the soft off state. This is definitely a little low given straight rectification of household AC. Obviously it wasn't a dead short though.
Replacing the cap with the 68 uF fixed the monitor fully.
~~~
To be more helpful I'll describe its behavior and other stuff I noticed.
Brightness Adjust:
I had recently turned up the brightness from about 33 to 66.
Erroreous Shut Down:
When I turned it on the day it failed, the backlight would turn on but would be visibly flickering. Then after a short delay, maybe 2 seconds, it would power itself back down. I could power it up again with the button but it would keep doing the same thing.
Noisy:
Various different components on the invertor and power supply board were making various noises. The noises only occured while the backlights were still on. I probed the noise sources with a long DRY CARDBOARD tube with which I could almost isolate to the individual component.
The loudest was on the power supply board in the area between the first yellow transformer and the two little toroids (closest to the AC plug). This was kind of like a crackly buzz. I associate the two toroids are fed in series to the transformer and by some manor or another that circuit drives a full wave rectifier to charge the great big 180 uF 450 V cap. With the cap shorted I attribute the buzz to excessive current in the toroids and possibly the transformer and possibly saturation of the core as well.
There was also a seperate crackly buzz coming from the later stage transformer but it was weaker. I didn't trace out electrical connections but I am guessing this was some kind of swicther and the buzz was due again to excessive current but this time due to insufficient reservoir (input voltage) requiring longer and heavier switch cycles.
There was also a weak crackling noise coming from the large black magnetic components on the inverter board. This probably had something to do with power supply noise, low voltage, or periodic dropout.
The power delivered from the power supply was about 18.5 V when on and 18.8 V when off. This fooled me for a bit to think the power supply part was working but it wasn't fully working.
Unfortunately I didn't measure voltages once it was working. I was just happy it worked.
Once I replaced the big cap, the backlight came on perfectly and stayed on, and any noise was virtually gone.
~~~
I'll reveal that I had this monitor nearly completely disassembled before figuring out the real problem.
It was pretty easy to do. You just want to be very gentle with the LCD and the circuit film leaves attached to it. Also try to keep anything between the back side of the LCD and the front side of the 1 cm thick diffuser very clean because any debris that gets in there I am pretty sure will show up in the picture forever or at least until you open everything up again to get it out.
There are two CCFL modules. One at top and bottom. Each are about 16.75" long. Each have three CCFL tubes slightly larger dia. than a pencil lead. But remove your own and get exact form factor before buying some . . .
All six tubes worked in mine, yet there were some dark specs at the end of a few when off. Usually any kind of dark spots would seem to mean bad but in this case they might be the mercury that is in them condensed when they turn off which would be normal. That is a guess. Or it could be signs of aging, but they still work just fine.
It would be pretty easy to retrofit with LED backlights.
As budm pointed out you will still need a 19V power supply to deliver to the buck boost/USB board which will then derive power for the logic board.
You might replace the existing power supply entirely or you might leave that and re-purpose the provided 19V out to drive and LED driver. The invertor would definitely be eliminated.
In addition to the 19 V from the power supply to the invertor, there were three signals shared by the logic board. These I think are the brightness control and possibly brightness feedback. I don't know which one is which though.
You would need to determine how to translate these signals for the LED driver to maintain the ability to control brightness from the 2007FPb on screen menu.
Another pointer is that I was able to run this without the LCD component connected. Removing that from the system (and from the work area) is a good Idea while diagnosing problems that aren't related to it. Simply because it is delicate and clunky.
One final thing, this monitor uses a little bit of power, not sure how much, just by being plugged in. You might want to install a switch so it can be switched off a shoulder height or plug it into an external power strip that you can kick off with your foot to save power, and save working life of the display as well.
Good luck. Hope this helps you fix your nice display.
Be SAFE!
Comment