Dell E172fpb

[davmax]

Re: Dell E172fpb

Unfortunately it was stated that it did not matter whether the inverter or lamp was bad.

The first step is elimination. If you swap the lamp leads and the problem moves to the other inverter you have a lamp problem. If it does not you have an inverter problem.

[HOODLAM]

Re: Dell E172fpb

Hi guys! just an update. MY PARTS ARRIVED!!! and as you can guess, i am using the screen at the moment.

Thanks for all the input and info.

[Krankshaft]

Re: Dell E172fpb

Nice work. We're glad to help.

Just remember to make sure that the monitor is turned off during the POST this will prevent the trannies from giving you problems again.

The monitor I'm using on this comp right now is the same HP you have and its been working for months now without problems.

[Pentode]

Re: Dell E172fpb

Hi All.
New Here.
Well, My BenQ FP737s is up and running again, using MJE3055's, with the mounting tabs filed down a couple of mm.
(Thanks to all posters).
Initially after fitting these, it worked fine, but seemed to be getting hotter than hell.
It finally gave out, and I had to open it again.
I was about to place an order for the proper 2sc's, until I took a closer look at the PCB's solder side, particularly arount the four transformers.
Yup! One of the solder joints on one of the transformers looked fractured.
A "dry" joint.
I resoldered most of the joints on the board, and re-fitted.
All seems well for now.
There is still some heat generated by the transistors, but considerably less than before. Time will tell. I may still get the 2SC's.
Cheers.

[HOODLAM]

Re: Dell E172fpb

JUST AN UPDATE! TOUCH WOOD, SCREEN STILL WORKING PERFECTLY! IT MUST BE BECAUSE I BOUGHT SPARES FOR JUST INCASE.

[Krankshaft]

Re: Dell E172fpb

I felt the same way after my repair.

The HP is my new primary monitor been using it for months.

[banjes]

Re: Dell E172fpb

The MOSFETs, fuse and 2SC5707s are the major components that are likely to be affected. The Dual controller chip should survive OK being isolated from each MOSFET by a current limiting resistor. However you should check out the two MOSFET driver transistors they are under the board with three legs. Check for shorts. You should be able to compare the transistor reading in the two driver circuits, naturally they should be the same unless one is faulty.

I am surprised to hear that that Benq agent did so badly, possibly put the apprentice on the job.

Hi , do you know what type the two MOSFET drivertransistors are (under the board with three legs). I have replaced de 4 C5707 and the two 9024. I have not powered on , because there is a different between comparing the two 9024 and I think it has to do with the drivertransistors (under the board with three legs).

[banjes]

Re: Dell E172fpb

I am for sure that Q804 is defect, but I do not know the type of drivertransistor I can use for it.

[Krankshaft]

Re: Dell E172fpb

Take a picture of the component we'll see if we can help.

[banjes]

Re: Dell E172fpb

Take a picture of the component we'll see if we can help.

Hi, thanks for your attentions and hereby I send the board of the picture and a detailed picture of the section with the faulty driver transistor.
The TFT is a HP1940 and the board number 48.L1G02.A00

There is a short on Q804 when I use my Digital Multitester. The short is between the upper middle leg and left under leg.

(as my mother language is Dutch I hope you understand my Englisch).

It is on this side of the board where the 2sc5707 and FU9024N also were defect. I have replaced them allready but not tested the board because when I was measuring on the two FU9024N I founded difference. So I examined the board further and discoverd the defective Q804 but .... I do not have further information on Q804.

Regards Frans

[Krankshaft]

Re: Dell E172fpb

Sorry for the real late response the SMT transistor in question is for the soft start circuit these little guys get the signal at their base from the main board and in turn they drive the larger transistor to turn the CCFLs on.

There should be a 3 digit code on the shorted transistor get a magnifying glass and let me know what it is.

I can look it up at a few cross reference sites that I know of and hopefully I can get you a full part number and where to get it.

[sydewinder99]

Re: Dell E172fpb

My Contribution,
After replacing the C5707 a second time. I decided to use the MJE3055. But instead of craming them in the same location. I mounted them to the main back frame. (See Attached PDF). There should be no heat issue with these mounted correctly there. This is mostly for newbies, but could give some ideas to the experienced folks as well. Hope this helps someone out.

Jay

[tattoum]

Re: Dell E172fpb

hi to all
i have a benq fp767 monitor that when i turn it on it works perfectly for 1 or 2 seconds then it becomes black and after some seconds it flashes for a 1 seccond then black again, and every timer i turn the monitor off then on it does the same thing. the green led is on and i can see the picture so its a backlight problem, i test the 4 c5707 and the 2fu9024n they are all ok. now i dont know what to do and what to check else please help me to repair it.
thanks to all helpers

[Krankshaft]

Re: Dell E172fpb

Check very carefully for cracked solder on the inverter board. This is a common problem and causes this issue.

Also check to make sure that none of the caps are bulged.

[tattoum]

Re: Dell E172fpb

hi again for my benq fp767 i found that the mcr100-6 has the cathode and the gate shorted from the 2 ways i dont know if it is damaged and if so could it be the cause of the backlight malfonction ?
thanks

[Krankshaft]

Re: Dell E172fpb

If you can please post a pic with the shorted part circled so that I can tell you what its for.

[juane414]

Re: Dell E172fpb

Hey all,
I'm new to these forums but have some questions. I have a BenQ FP757 that I saved from a dump heap at college. I does the same on for 2 seconds off again deal that the Dell's do. The power/inverter board in this one is extremely similar to the one in the Dell monitors. I was thinking about replacing the transistors and two capacitors that are bulging, but I noticed that this board actually has 6 transistors. Should I replace all of them? Also the capacitors are 470uF 35v and 105C. Where is the best place to get a couple of those?

http://i264.photobucket.com/albums/i...DSC01255-1.jpg

[weoxstan]

Re: Dell E172fpb

I too have this monitor with the flashing LED. I replaced the trannies with ones that I bought off ebay and resoldered about half the board and the monitor has been working now for about a month.

Just wanted to say thanks for all the good info here.

Jeff

[juane414]

Re: Dell E172fpb

Well, after replacing the bad transistors the monitor works again. But after I turn it off the lcd goes off, but the backlights stay on. Anyone know what would cause this?

[Krankshaft]

Re: Dell E172fpb

Yes there are two switching MOSFET that turn the 2 sets of backlights off.

They are probably through hole components on your Dell while they can also be surface mount your board looks more like a through hole design to me.

They will be somewhere around the inverter transistors you replaced just look up the part numbers on the unknown transistors at http://www.alldatasheet.com .

When you find a datasheet that says MOSFET look at the pinouts on the sheet for the FET and measure with the diode check function of your DMM.

Measure from source to drain and you should get voltage drop in one direction when you measure one of them it will be shorted in both directions replace it and the backlights will turn off again when you shut the monitor down.

The is a common problem on Benq inverters when the inverter transistor blows (shorts out) I theorize that alot of current is drawn through the FET for an instant (before the micro fuse blows) and in this short time it destroys the FET.