Dell E172fpb

[Krankshaft]

Re: Dell E172fpb

Wrong data sheet!!! However I know this controller chip and have data sheet.

Here is the datasheet for the inverter Dual PWM for people in the future.

[davmax]

Re: Dell E172fpb

Thanks Krankshaft. I have data sheet.

This chip is the same as in the Benq monitor I modified (Benq FP737s thread). I suspect that there is the same weakness that blows transistors ie a rapid OFF then ON of video signal bypasses the soft start timing.

It is amazing that the monitor in question worked with a subtitute N channel MOSFET. I ponder how it did work!!!!

[Krankshaft]

Re: Dell E172fpb

I am pondering that too I would think that it would have overheated and self destructed in short order.

Maybe it survived because its breakdown voltage was overkill and was able to bear the strain?

Installing the proper N or P channel FET is as elementary as making sure that the components pin out is correct.

They couldn't even get that right so comparing their electrical characteristics was way out of the question.

But after what I've seen so far I think this guy should be flipping hamburgers rather then working with electronics.

That fact that the component was replaced tells me like on my monitor when the driver transistor went it shorted out the FET in its circuit by destroying the fragile gate.

[HOODLAM]

Re: Dell E172fpb

Hi Guys. The Screen Went To A Company Called Vr Eletronics Who Are The So Called Benq Repair Agents Locally. Well, Something Tells Me They Aren't To Sharp There. I Just Hope I Can Repair What They Have Messed Up. Is There Anything Else I Can Check?

[davmax]

Re: Dell E172fpb

Hi Guys. The Screen Went To A Company Called Vr Eletronics Who Are The So Called Benq Repair Agents Locally. Well, Something Tells Me They Aren't To Sharp There. I Just Hope I Can Repair What They Have Messed Up. Is There Anything Else I Can Check?

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.

[davmax]

Re: Dell E172fpb

When you replace the transistors make absolutely sure they are replaced with the same orientation ie correctly connected. Watch out for lifting PCB track, making sure to detect any track break.

When you get the monitor going a good insurance is to switch off the monitor before you start the computer. This will make it certain that the monitor will not experience the soft start bypass that can occur and stress the 2SC5707 transistors. Turn ON the monitor late in boot or at completion.

[Krankshaft]

Re: Dell E172fpb

Installing the new driver transistors in the right orientation is easy on the PCB you will see a white line silkscreened on the board.

The metal side of the new driver transistor should face this white line.

[dbsoundman]

Re: Dell E172fpb

I have a somewhat different issue than others here...

I was using this monitor with my desktop computer, and everything was fine for about 4 months or so. Then one day my desktop tower would not turn on. I finally got around to troubleshooting today, and found it will turn on only if the monitor is not connected. So, I assumed that the monitor had issues. I tried the monitor out on my laptop, and it worked, but about 10 seconds later smoke started coming from where the monitor was plugged in on the laptop! I didn't have the cable actually screwed onto the laptop so I just yanked it out fast, but I'm guessing I have some sort of issue where the monitor is sending voltage back to the computer. Any guesses as to what is going on? I will go try to get the back off and see what I can see...

Thanks!
-Dan

[dbsoundman]

Re: Dell E172fpb

I just got the thing open. Everything inside looks perfect...so no direct suspects there, and I saw some of the components seem to be decent quality (nichicon). I did also notice that mine is the E172fpt and not fpb. I also did not see any markings indicating it was made by Benq.

Also considering the other side of the coin here...could it be that the PC tower's video card has the issue, and my laptop issue was some sort of fluke? I'm curious to hear what you all think. I'll see if I can borrow a CRT or something sometime soon to see if the PC will fire up with one of those attached...

-Dan

[HOODLAM]

Re: Dell E172fpb

HI GUYS, JUST THOUGHT I WOULD KEEP YOU UP TO DATE WITH THE PROGRESS REPAIRS ON MY HP L1955, WELL... STILL NO PARTS YET!!! HOPEFULLY STILL SOMETIME THIS WEEK!!!

[charlesrg]

Re: Dell E172fpb

It's still working good. No problems at all. No smoke either.

Today the transistors failed again, monitor is having the same symptoms.
I just bought 4 from this ebay for $7 bucks.
If it fails again I will just order the whole board for 40 bucks. It should fix the problem.
I will post more info when the components arrive.
Thanks

Also about the RadioShack components, yes, they are bigger and I had to do a little cut on the case to make them fit.

[Krankshaft]

Re: Dell E172fpb

Have you been keeping the monitor shut down during the POST?

If you have been leaving the monitor on during the CMOS check then the soft start circuits are being bypassed stressing the driver transistors you replaced.

If so thats the reason why they kicked the bucket again.

[HOODLAM]

Re: Dell E172fpb

Update Time!! Some Of The Parts Arrived Today! Just Waiting For The 9024n's Which Should Be Here In A Weeks Time. Will Continue Installing The Components!

[peterrr]

Re: Dell E172fpb

Hi everybody..
Short description: I replaced 9024 & 5707 but after 2 minutes they burn again (one 9024).. I decided that one working ccfl will be enough.. My plan is to desolder failed 9024 - this will disconnect faulty circuit for second ccfl.. Whats happened: LCD working fine but backlight is getting off after 2 seconds.. I think i need to put feedback1 (IC751) from working circuit to disconnected circuit feedback2 to cheat IC751..

What you think?anybody

[Monitor Doctor]

Re: Dell E172fpb

To peterrr and Hoodlam,

That other site that charges $20 shipping that is nuts man. You can get those parts 2SC5707 and the FU9024N and shippin just $6.95 anywhere in the world from lcdrepairparts. They also claim to provide the some real simple solution to prevent them from blowing out again. The web address is http://lcdrepairparts.com

peace!

[davmax]

Re: Dell E172fpb

To peterrr and Hoodlam,

That other site that charges $20 shipping that is nuts man. You can get those parts 2SC5707 and the FU9024N and shippin just $6.95 anywhere in the world from lcdrepairparts. They also claim to provide the some real simple solution to prevent them from blowing out again. The web address is http://lcdrepairparts.com

peace!

Hi Monitor Doctor. Are you part of lcdrepairs? Your name appears on the web site.

I would be very interested in the detail of the simple repair that prevents future blowing of the 2SC5707.

I will give you the benefit my experience with the Benq FP737s monitor. Fortunately I was able to get a schematic that identified that the 2SC5707 transistors were not well protected, in fact this particular design has a useless circuit for transistor protection. I therefore designed and installed a 10uS response over current protection that really protects. Having installed this protection that actually trips off the power to the inverters I was able to witness the cause of transistor failure. Failure can occur if a computer removes the video signal and rapidly returns it. This causes a bypass of the inverter slow ramp up and excessive transistor current has been seen to occur, presumably due to inverter transformer saturation. The trip circuit provides absolute protection and as said already allows witnessing of excess current conditions.

Another protection method that does not provide absolute protection of all over current conditions is to install a small monstable circuit that monitors and controls the video control signal to the inverter power. This circuit ensures that once the control signal is removed that it cannot return for 1 second or more thus allowing the ramp circuit a recovery time.

Hope you find this helpful

[Krankshaft]

Re: Dell E172fpb

Hi everybody..
Short description: I replaced 9024 & 5707 but after 2 minutes they burn again (one 9024).. I decided that one working ccfl will be enough.. My plan is to desolder failed 9024 - this will disconnect faulty circuit for second ccfl.. Whats happened: LCD working fine but backlight is getting off after 2 seconds.. I think i need to put feedback1 (IC751) from working circuit to disconnected circuit feedback2 to cheat IC751..

What you think?anybody

One of your High Voltage transformers is fried causing the transistors to blow.

[peterrr]

Re: Dell E172fpb

Thanks for answer. But i dont understand why is backlight getting off after 2 seconds in working ccfl circuit..? failed circuit is disconnected.

[kc8adu]

Re: Dell E172fpb

the controller senses the failed lamp didnt strike so it shuts down.
does not matter if the lamp or inverter is bad.

[peterrr]

Re: Dell E172fpb

the controller senses the failed lamp didnt strike so it shuts down.
does not matter if the lamp or inverter is bad.

Then what is solution? i need to do something with controller?