Dell E172fpb

[Acton-Hilton]

Re: Dell E172fpb

Hi folks
I'm new to this forum - but not to monitor faults!
I have had this problem in the past, with other monitors with a backlight...it seems that the cold cathode backlight tube dies & cannot conduct...thus allowing the voltages at the transformer driver transisters to rise above their working voltages due to no load & fail......
Is it possible to replace the cold-cathode tubes in these particular screens?, if not I suspect it is all a waste of time. A new screen will cost more than the monitor & you still have to change the transisters too...
In this one that I have just opened up the same Q759 & Q760 are shorted all ways!
Bob UK

[greenfirecracker]

Re: Dell E172fpb

Ok this is my assessment of source of the problem, the source is not in the power board but in the video board. For some reason the adjust out of the video board does not respond to the brightness buttons on the front panel at all. This would be pin one of CN701 to the video board. The video board gives a constant 86% duty cycle and constant frequency out for me and does not change. My guess is this is what is overdriving the transistors. The nice thing is if you remove resister R750 top/right on the power board the panel goes to a default brightness which is plenty for me. Of course I did have to replace the bad transistors on the power board. The transistors stay nice and cool for me after removing this resistor but if I reconnect it the transistors start cooking. My guess is you could fab a 555 timer to take control of the brightness if its that critical for you. If anybody finds out why the video board doesn't respond I would like to know but im not spending any more time on it. Hope this helps.
kevin

[CudaDave70]

Re: Dell E172fpb

Hi ,I have read this entire board about 2 am when I finally threw in the towel. I am trying to get this Dell E173FPb running again. Been apart about 20 times ,Think I might be getting lead poision already. I have tried all of the suggestions tests ect that I am capable of doing .I got the big old oversize MJE 3055 trannies,That many post suggested using .
I have cut out the side so they fit (like a saddle on a cow). I have done everything I think possible. It would actually run hours witn out shutting down some times,till I did something like move or touch it. I thought "I got it" at least half a dozen times. But the result at the end is a dark screen,little green diode flashing (laughing )at me every time. I thought to myself,what do all these monitor have IN COMMON (there are sooo many on ebay that have the identical symtoms). I thought that crummy little terminal that connects the ccfl to the board. I would move these around and the panel would flicker some and mostly shut down(I didn't find this out till the day before yesterday ) . I had my most luck with it when I soldered the ccfl leads directly to the pins on the board. I knocked it around shook it banged it against the table ,didn't shut off at all. But I had a defective tube that would not restart once you shut off the monitor and tried to fire it again .You could see a spot on the bottom of the lcd panel when it tried to light up again like a rainbow shape only with out the colors. I believe these (relaxing with the heat )clips may be part of the problem . I replaced the tubes with others cleaned the pins up plugged the new (used) lamps on the pins .It fired up and ran along time before it shut down about 1 hour . I suspect the same thing with the loose pin connections that are falsely tight because of the plastic plugis tight. Think about it ,they are probably expanding as they heat up. The way they are made there is a VERY SMALL amount of contact with the pin. I am going to try and solder the new (used but working)ccfls and put the correct transistors in because I have a space heater of a desk top already.The 3055 trannies get as hot as 250 F degrees ,I checked them out with a heat gun and a probe to be certain,I saw temps normally around 150 F. What do you all think about this? ,Something I would have never thought about till I saw that thIng blink and shut off when I moved the wires and put the steel cover on. I am trying to get 2 monitors working out of the 3 I have here. Boy It hurts when you get zapped with that high voltage on those wires. Here are a few pics of what I am saying. also the transistor size difference for those who are coming on board for the first time. I call it the winter transistor cause it runs so hot.The little on is one that s--t the bed,you can see the hole and how loose this plug is if you zoom in .

[arneson]

Re: Dell E172fpb

My first suspicion on failing inverters is the high voltage coupling caps.
I think they may look all blue and shiny but tend to ark internally.
I only say this becuase I"ve seen so many of them completely burnt black.
If they snap it can harm the tubes, the transformers and the whole inverter becomes unhappy.
They are cheap and easy to pop in even just as insurance against failure.

[CudaDave70]

Re: Dell E172fpb

I absolutely agree about replacing caps ,I did do that . all that desoldering and soldering made me almost blind. I changed all the caps except for that 450 volt one could it be that one? here are better pictures.This pin pictured is really loose it would definatelycause a loose connection

[CudaDave70]

Re: Dell E172fpb

Sorry, Jim ,my mistake you meant those little blue caps that go between the high voltage outlet of the transformers amd the output pins on the ccfl sockets. My goof. No I did not change those ,never read anything about them going bad, thanks for that advice and I will do that as soon as I can figure out what they are as far as a part # or is this something that is common to all invertors .I am flying by the seat of the pants here and relying on alot of good smart people on here to get me straightened out.I am an old dog trying to learn some new tricks.
Here is that transistor picture I can't seem to get posted.

[arneson]

Re: Dell E172fpb

Just remember that this is high voltage at that point. They are 3kv caps.
So you don't want any solder spikes or leads sticking up.
There is even sometimes an air gap in the board under them to keep the arking suppressed.
If you fire up your laptop for any length of time,
just run your hand along the lower edge of it's screen.
Those inverters have been made so small that they get hot, very hot.
Many are wrapped in flame retardent material.

[CudaDave70]

Re: Dell E172fpb

OK Jim ,I have learned that there is some serious power there. I accidentally pulled one of those ccfl plugs out while it was running(I guess it don't shut down when it is trying to arc weld) . I am not kidding the arc burned the plastic as it was going to ground like a little lightning bolt .I panicked grabbed it to pull the power plug out of the bottom and I got a large dose of some p-ssed off electrons. Got a good shock 2 times already from that bad boy.There is some new found respect happening here.I really don't understand where it goes to 12 volts,I assume there is 12 volt somewhere on this board I thought it was at the large transformer ont the safer side of the board. I wish I had the schematic for this dell e 173 FPb.

[cravenarts.com]

Re: Dell E172fpb

... The nice thing is if you remove resister R750 top/right on the power board the panel goes to a default brightness which is plenty for me. Of course I did have to replace the bad transistors on the power board. The transistors stay nice and cool for me after removing this resistor but if I reconnect it the transistors start cooking. ...
kevin

Your solution is so simple but that's what makes it great. I tried it and it works, but is there any risk to other components by doing this?
What do you think about replacing the resistor at R750 with a stronger resistor?

[CudaDave70]

Re: Dell E172fpb

The removing of the resistor is a great Idea ,sort of like a governor on an engine to keep it from running wide open all the time . I did it and so what ,it is definately bright enough for anybody .
My newer Dell monitor has no adjustment for brightness. Maybe they also found this out. The changing of the resistor in the circuit sounds like it would have to be an experimental, trial and error deal.
I doubt if removing the resistor could hurt any other components. circuit, the same thing would be accomplished by setting the brightness to a lower level and rig the button so it can't be pushed again.I chose to take out the resistor.I love these easy fixes ,thanks, Kevin
Dave

[CudaDave70]

Re: Dell E172fpb

Wicked when it has nowhere to go, I just took apart another monitor I picked up . I found one of the plugs messed up (somebody tried fixing it before) looks like the ground was lost somewhere along the line . I couldn't believe how it burned through the plastic housing ,burned the wire off and cooked the rubber insulator and lamp holder.Or just maybe they had the high voltage post connected to the skimpy little groung wire. I was impressed how it bored it's way out seeking a ground,bet it stunk a little when it happened.

[CudaDave70]

Re: Dell E172fpb

Anew developement with my dell (pita) W173 fpb. It worhs beautifully since I changed the power fuse at 751 ,only thing now the back light stays on when you shut the thing off or the computer off now,it works too good, AHRRRRGH.

[arneson]

Re: Dell E172fpb

Nice design for a fancy night lite there dave.

[greenfirecracker]

Re: Dell E172fpb

Im realy glad this worked out for you, I cant imagine that removing this resistor will have any negitive effects on other parts of the board. My monitor has been working great since the removal and I run it 24/7 sometimes. I dont think a larger resistor will help anything, from what I can tell this is probably a duty cycle controlled circuit and not a current controlled nor is this resistor set up as a voltage divider. so you will likely need an external circuit with variable duty cycle to control the brightness. but I wouldnt be 100% sure untill I got a monitor with a working brightness and checked with an O.scope. Note if you do use an external circuit like a 555 make sure you use the same ground that comes from cn701 good luck.
Kevin

[CudaDave70]

Re: Dell E172fpb

Anybody have an Idea for me on the
"one side stays on" ? It has reduced voltage(around 8 -9 volts) going to the two transistors on one side when I power off the monitor The ccfl's on that side stay lit as long as the cord is plugged into 110 volts.

[CudaDave70]

Re: Dell E172fpb

I'll take this as a "you'll figure it out,swim or drowned " I could get lucky you know.I'll throw some more parts at er.

[greenfirecracker]

Re: Dell E172fpb

dave without looking I would guess you shorted one of your switching transistors when you resoldered your board. or shorted something else.
thats the best I can do, sorry
kevin

[CudaDave70]

Re: Dell E172fpb

Well thanks Kevin, I finally discovered what caused that problem. There are 2 more similar looking transistors on that board ,only by trial ,error ,reading , and guys like yourself helping me. I discovered that Q743 and Q741 are there to turn the power on or off to the four trannies: Q739, Q740, Q759, Q760, that I had replaced earlier in this story. I have this one circuit board I call the guinea pig board and it looks as if something like a pit bull had it . It has wires soldered all over it because some of the copper traces are gonzo. These two transistors are also prone to fail sometimes in addition to the other four C5707. I checked voltages when you power on with the green-yellow LED on-off button ,the voltage spikes to well over twenty volts to those four switching transistors,I would bet that can be pretty hard on those little tri legged buggers.I really don't know how much for sure because my meter is really slow to respond so it could be lots more than 20 v. It would be similar to the ole lady gettin you up in the morning by throwing a pot of hot coffee on your nuts . No wonder they have a hard time making it past the five year mark.
Dave

[Sixpence]

Re: Dell E172fpb

Hi guys, I'm new member, and just a hobbyist. I picked up my Benq FP737 at the Thrift store for $10, because it looked real good condition, despite its led's lighting up but no display. Google got me to this great forum - thanks for everyone's helpful postings.

I've replaced all four C5707's and rigged little heatsinks onto them. My board had ST 010pf06 FETS in Q743 & Q751 positions, which I replaced with the 9024N's - assuming these are equivalents?

No caps look puffed, but I replaced all the 470uF and 1000 uF elcaps anyway, and also the 3A fuse, which was dead. Lastly, disconnected the R750 resistor, and re-soldered the transformers, high voltage caps, the two big diodes and lamp sockets, etc.

It's 2am now, and I've just discovered my "little" heatsinks touch the metal backplate, so I'll have to cut them down some! I'll post later in the weekend whether mine's running ok now.

[Sixpence]

Re: Dell E172fpb

Nope. I let the computer boot before plugging in the power to the FP737 and switching on - quick flash of Benq logo and blackscreen. Led still lights steadily.

Any suggestions would be welcome!