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Old 01-17-2006, 07:34 PM   #1
syclonejim
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Unhappy Dell E172fpb

I have a Dell E172fpb 17" lcd manufactured by BenQ. It will not power on, the power button justs blinks green and the screen flashes. I have taken the panel apart and examined the power inverter board. There are no bulging capacitors, but it is full of Lelon caps. I have seen on this forum that this brand is considered one of the least desireable. Anyone have any experience with this LCD panel or problem? I have done several other capacitor repairs, but always the sure tail sign(bulging).

Last edited by syclonejim; 01-17-2006 at 07:37 PM..
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Old 03-01-2006, 02:39 PM   #2
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Default Re: Dell E172fpb

Quote:
Originally Posted by syclonejim
I have a Dell E172fpb 17" lcd manufactured by BenQ. It will not power on, the power button justs blinks green and the screen flashes. I have taken the panel apart and examined the power inverter board. There are no bulging capacitors, but it is full of Lelon caps. I have seen on this forum that this brand is considered one of the least desireable. Anyone have any experience with this LCD panel or problem? I have done several other capacitor repairs, but always the sure tail sign(bulging).
I have the same 17" Dell/Benq LCD Monitor with the same problem. Do you have any advise for me on a fix for this monitor? -- Any help would be great!
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Old 03-01-2006, 06:52 PM   #3
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Default Re: Dell E172fpb

post a pic of the inverter and logic.
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Old 03-11-2006, 10:05 AM   #4
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Default Re: Dell E172fpb

I have the same monitor for repair, pics as requested...

Regards

Richard
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Old 03-11-2006, 06:16 PM   #5
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Default Re: Dell E172fpb

This board was a little bit confusing at first to determine which connectors are not at mains potential. CN701 (and CN753) are safe to measure, because there appears to be a blank area of PCB between it and the primary side.

The first area to make measurements is CN701 (low voltage power supply). Also measure the output on diodes D751 and D761. Take care when measuring CN752 and CN753. You may need to measure voltage between each pin of these connectors, instead of GND.
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Old 03-11-2006, 06:38 PM   #6
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Default Re: Dell E172fpb

CN752 and CN753 are high-voltage supplies for backlight - I'd not mess with that. It either works (backlight lights) or not (backlight does not work but everything other does - if you light it up with something strong, you can see picture).
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Old 03-11-2006, 06:45 PM   #7
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Default Re: Dell E172fpb

Quote:
CN752 and CN753 are high-voltage supplies for backlight
what is backlight getting, i thought it was 12v?
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Old 03-12-2006, 01:00 PM   #8
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Default Re: Dell E172fpb

Symptoms...

If the monitor is connected to a PC (in windows or whatever), when you first power it up, you get a very quick flash of the windows desktop on the display. The power LED then starts flashing at a rate of around 1 flash per second.

I have taken voltage readings at CN701... Pins 9 & 10 pulse 3.3V, but as i'm using a Digital VM, it seems to fluctuate between 1.5 and 3.3V. Pins 7 & 8 pulse between approx 2 and 5.0V. Pins 3 - 6 are GND.

If you listen closely to the board, you can hear a "tick" when it pulses... my hearing is not great, so i can't pinpoint where the "tick" is coming from...

If anyone is interested, I've attached a pic of the under-side of the board.
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Old 03-12-2006, 02:00 PM   #9
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Default Re: Dell E172fpb

The bottom of the PCB is discolored so it certainly runs hot. Maybe some of the caps are dried out. If they're crap brand, they can go fast.
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Old 03-12-2006, 02:05 PM   #10
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Default Re: Dell E172fpb

here is an interesting thread
http://www.network54.com/Forum/87612...9/DELL+E172FPB

regarding the caps, those elna style vents suggest koshin caps. i would be interested to know if they test off spec.

its hot in the region of the fets.....

Last edited by willawake; 03-12-2006 at 02:09 PM..
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Old 03-12-2006, 02:42 PM   #11
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Default Re: Dell E172fpb

the ticking suggests the pwm is starting and then hitting the overcurrent limit.
or lack of feedback from the opto causing same.
i would change out any caps in the darkened areas anyway.
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Old 03-12-2006, 02:59 PM   #12
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Default Re: Dell E172fpb

on that thread i linked they had some fets going bad. but there has got to be a reason for that? badcaps running fets hot? or just bad design

i would sink them anyway once you get that up an running. looks kinda toasty there. edit : actually forget that some are sinked the others impossible.

Last edited by willawake; 03-12-2006 at 03:03 PM..
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Old 03-12-2006, 03:30 PM   #13
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Default Re: Dell E172fpb

Ok, on my board, the blue caps are brand new (maybe still crap, limited stockists nearby and not enough time to order over the net), labeled C751, C703, C712 C709, C707, C708 and C710.

D701 and D702 are UGF10DCT Diodes (with sinks).

Thanks for the link willawake... Looking at that, it looks like the same problem I have, so, does anyone know of a stockist in the UK that has some 2SC5707's (Edit: or equiv) (in lower quantities than 700)? Quick google didn't reveal much...

Thanks for all the help!

Last edited by HelpQuick; 03-12-2006 at 03:32 PM..
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Old 03-12-2006, 03:36 PM   #14
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Default Re: Dell E172fpb

you should test them before ordering. guys please explain again how to test fets.

digikey will supply if rs/farnell/elfa dont have

better to recap also anyway for a final repair, it is not too many caps.
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Old 03-12-2006, 04:02 PM   #15
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Default Re: Dell E172fpb

If there's something shorted (like one of the transistors), you can find it using "beep" multimeter function.
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Old 03-13-2006, 01:05 AM   #16
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Default Re: Dell E172fpb

Thanks all for your help...

I tested the transistors Q759 and Q760 were shorted, I have swapped these, and the monitor now works great!

Once again, Thanks to all who helped!
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Old 03-28-2006, 11:29 PM   #17
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Default Re: Dell E172fpb

I have the exact same monitor and as of tonight the same exact symptoms.

I pressed the power button and it broke. At this point the monitor started to flicker on and off once a second with the green light pulsing at the same time as well as a small click or chirp.
I took it appart and can not see any damage to the actual led or switch.. just the button is broken on the monitor face.

I can see no damage to the small board the led and switch is connect to.

Luckily I have someone here who is familiar with working with boards and they will take a look at it.

Thanks for the info.
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Old 03-29-2006, 12:47 AM   #18
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Default Re: Dell E172fpb

The monitor that i had fixed with the help of this forum has once again failed... this time, the monitor works for around 2 hours, then goes off with the original symptom.

If it's left off for a while, it can be used again for about 2 hours (presumably some sort of thermal problem)

I haven't had a chance to look at it again yet, but will let you know how i get on.
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Old 04-23-2006, 12:02 PM   #19
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Default Re: Dell E172fpb

Hi, I am new here and I have the same problem with the monitor. The first problem is that I don't know how to open the monitor -_-, Plz help.
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Old 05-08-2006, 09:12 AM   #20
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Default Re: Dell E172fpb

Many, thanx for the solution, the trannies are shot.
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