Dell E172fpb

[sandltechnologies]

Re: Dell E172fpb

I think from the posts this may not be the best screen to work on...

My symptoms are screen turns on displays the dell test image red green blue white moving box then goes dim. I have recapped the 5 470uF 35V caps transistors do not show shorts I have retouched all the solder on the board as well. I am at a loss at the moment seeing as how no caps are bulging even the 5 I repaced weren't leaking or anything. What part of this circuit should I forcus on? Here are images of my board the blue caps are the replacements.

[EGuevarae]

Re: Dell E172fpb

I think from the posts this may not be the best screen to work on...

My symptoms are screen turns on displays the dell test image red green blue white moving box then goes dim. I have recapped the 5 470uF 35V caps transistors do not show shorts I have retouched all the solder on the board as well. I am at a loss at the moment seeing as how no caps are bulging even the 5 I repaced weren't leaking or anything. What part of this circuit should I forcus on? Here are images of my board the blue caps are the replacements.

1.- replace caps
2.- check/replace the c5707s
3.- check/replace the 2 fu fets
4.- retouch all solder points,specially transformer ones
5.- try to get another set of lamps to test ...

[sandltechnologies]

Re: Dell E172fpb

1.- replace caps
2.- check/replace the c5707s
3.- check/replace the 2 fu fets
4.- retouch all solder points,specially transformer ones
5.- try to get another set of lamps to test ...

Did replace caps at least the 470micro ones as thats what I had in stock.

Transistors checked with no shorts.

Checked solder points did add solder to a few spots that looked iffy

I actually have another dell screen here same setup but with same problem, but it is a E172FPb. I haven't had any luck with either board/screen.

[EGuevarae]

Re: Dell E172fpb

Did replace caps at least the 470micro ones as thats what I had in stock.

With what?

[retiredcaps]

Re: Dell E172fpb

My symptoms are screen turns on displays the dell test image red green blue white moving box then goes dim.

1) If you hookup a working computer with your favourite wallpaper, do you see it?

2) If you shine a flashlight on the lcd, do you see the wallpaper?

3) Does screen come on for 2 seconds and then go black?

I have recapped the 5 470uF 35V caps

Let me guess, you got these caps from Radio Shack?

If yes, Radio Shack does not sell low ESR caps which are required on the power board.

[sandltechnologies]

Re: Dell E172fpb

1) If you hookup a working computer with your favourite wallpaper, do you see it?

2) If you shine a flashlight on the lcd, do you see the wallpaper?

3) Does screen come on for 2 seconds and then go black?



Let me guess, you got these caps from Radio Shack?

If yes, Radio Shack does not sell low ESR caps which are required on the power board.

Yes as I said it is just dim looks similar to a CCFL or an inverter going out in a laptop, but with a few seconds delay... Thanks to self test technology we don't need a computer to test screens anymore not even that crazy little box that makes rectangles with the 9V battery. Planning on pulling transistors and checking them with the huntron tomorrow should show me the correct graphs I guess I will start there even if they have capacitance or something else inside skewing them from their normal working area.

Yes, both screens show the same kind of come on little self test scrolls a little bi screen goes dim use my desk lamp can still see the image. Don't assume I know nothing because I haven't posted before this site has given me p/ns for components that lost all their magic smoke.

And no we buy all our supplies through mouser - generally do motherboard repairs on towers.

I did redo every solder connection on one board and it started working again. Didn't see any bad solder joints, but I guess that was one of the problems. I did read this entire thing last night and slept on it... So it was very helpful so far....

[alexanna]

Re: Dell E172fpb

^ No one is assuming that that you know little, we just have to start somewhere.
Have you done anything to rule out a ccfl problem? I am sure you know just one failed or marginal ccfl can cause the problem you are having.

[jetadm123]

Re: Dell E172fpb

First of all, you get a gold star for reading all 23 pages of this thread! Due to the age of this monitor one or more of the CCFL tubes could be drawing excess current, causing shutdown. Do you have any spare CCFL tubes that you can substitute one or two at a time for the existing CCFL tubes? If you don't have spare CCFL's try connecting some of the CCFL's from the other monitor you have in different combinations to see if you can get all 4 tubes to stay lit.

[kaboom]

Re: Dell E172fpb

I would like to give some transistor subs for the 2SC5707 as well as share another E172FPB story.

Just had one of these monitors, top backlight inverter dead as usual. One transistor shorted, one open. Complaint was 'lines through the screen' suddenly. When the inverter transistor(s) shorted, ripple from the 'brightness control' buck converter operating into a short was modulating with ripple from the (poorly filtered due to craps) power supply. The lines on the screen were the resulting beat notes that not only got TO the signal board, but went THROUGH it.

Plenty of poor joints on the four tuning caps as well as the jumpers in and around both inverters. Resoldered entire backlight/power board and recapped. Capacitors were Nichicon PW, except B+ filter cap, which was Nichicon PZ. Tubes were OK.

(Mouser P/N's)

B+ filter cap:
647-UPZ2D151MHD

Backlight power/15 volt supply:
647-UPW1E681MPD1TD

5/3.3V:
647-UPW1A122MPD

All others, including signal board:
647-UPW1H101MPD
647-UPW1H100MDD1TD
647-UPW1H4R7MDD
647-UPW1H2R2MDD
647-UPW2A010MDD
647-UPW1J680MPD
647-UPW1E220MDD
647-UPW1E100MDD

Transistors:
757-2SC3074-Y(Q)
512-KSD1691GS

This unit will only ever operate on 120 vac (USA), so instead of a 400/450 volt cap, I used a 200v unit for the filter cap.

Both of those transistors work.

Here are some measurements of what the inverters draw, lamps connected, with power applied between cathode of the diode in the brightness buck converter and the heatsink of the 15 volt rectifier:

5v test supply 15v test supply thru 10ohm resistor 15v test supply
2SC5707 210mA 690-710mA 1.38-1.45A
2SC3074-Y same same same
KSD1691G same same same

Got it back together and tested for 4-5 hours, and returned to owners. It's been two days and they tell me all is well.

-Paul

[el3ctroded]

Re: Dell E172fpb

I just wanted to submit some info I found about the Benq inverter circuit:

The C5707 is not used because of the high current capability, nor for it's high gain (hfe), nor for it's high Vce of 80V. It appears to have been chosen for it's low output capacitance, and possibly it's low Vce Saturation voltage.

I have determined this by trying several different transistors while looking through my existing parts to repair a monitor I had without having to order more stuff right now.

I found that a TIP120, which has a similar hfe but higher Output capacitance would not work. It overheated quickly, likely due to it's inability to switch fast enough with it's relatively high output capacitance.

In the past I used a TIP3055, which has worked well, and is still in use today, but they get warmer than the c5707s. The TIP3055 has a low hfe, low Vce(sat) and little higher output capacitance compared to the C5707, so I knew the gain was not important, but likely the Vce(sat) or output capacitance was.

I then tried a MJD44H11. It works beautifully. It has a low gain, low output capacitance, and relatively low (but higher than a c5707) Vce(sat).

El3ctroded

[jetadm123]

Re: Dell E172fpb

I just wanted to submit some info I found about the Benq inverter circuit:

The C5707 is not used because of the high current capability, nor for it's high gain (hfe), nor for it's high Vce of 80V. It appears to have been chosen for it's low output capacitance, and possibly it's low Vce Saturation voltage.

I have determined this by trying several different transistors while looking through my existing parts to repair a monitor I had without having to order more stuff right now.

I found that a TIP120, which has a similar hfe but higher Output capacitance would not work. It overheated quickly, likely due to it's inability to switch fast enough with it's relatively high output capacitance.

In the past I used a TIP3055, which has worked well, and is still in use today, but they get warmer than the c5707s. The TIP3055 has a low hfe, low Vce(sat) and little higher output capacitance compared to the C5707, so I knew the gain was not important, but likely the Vce(sat) or output capacitance was.

I then tried a MJD44H11. It works beautifully. It has a low gain, low output capacitance, and relatively low (but higher than a c5707) Vce(sat).

El3ctroded

Thanks for sharing. It's always good to hear about substitutions for the OEM parts. Radio Shack has the TIP3055 (a little pricey and it's a T-220 case, but if you don't wanna wait....) and Digikey carries the MJD44H11.

[lessthanchris1]

Re: Dell E172fpb

Found one of these monitors the other day. The screen is dark, but I can see images on the LCD with a flashlight. I took it apart, but the caps all look ok and the solder joints also look perfect on both boards.

Is there a way to check if the ccfl lamps are bad? I'm still in the process of reading all 23 pages, made is about 1/4 of the way through...

[Scenic]

Re: Dell E172fpb

^ it's "only" 12 pages when you set it to 40posts per page
https://www.badcaps.net/forum/profil...do=editoptions

[pamr4]

Re: Dell E172fpb

After you replaced those 4 C5707, you have to replace and those 4 caps between c5707.

[PlainBill]

Re: Dell E172fpb

Found one of these monitors the other day. The screen is dark, but I can see images on the LCD with a flashlight. I took it apart, but the caps all look ok and the solder joints also look perfect on both boards.

Is there a way to check if the ccfl lamps are bad? I'm still in the process of reading all 23 pages, made is about 1/4 of the way through...

Have you checked the Picofuse?

PlainBill

[lessthanchris1]

Re: Dell E172fpb

Have you checked the Picofuse?

PlainBill

I had no idea there was one. I see it now, PF 751. I will check when I grab my meter, its at home, i'm at college. It looked like a regular diode. I have three of the lelon caps that everyone says are bad, so I will start by checking the fuse and replacing the caps. At this point, the panel is from 2003, so I'm not sure the ccfls are any good to begin with... They don't look burned..

More to come when i grab the meter!

[Rtech]

Re: Dell E172fpb

The CCFLs from these much older Dell Models, seem to be very good, and it is only rarely that I have to replace one...saying that, I have one for repair this morning,so you just know what the fault will be !!!

[AlwaysImpedes]

Re: Dell E172fpb

Hey, I have the same problem can someone help find the correct capacitors on Digikey? I have a DELL E198FPb with the same issue. I have taken the picture to board and removed two capacitors that were bulging with burn marks on top.
Here are the capacitor info:
1). Lelon -A701 (M) RGA 105c - 470uF, 16v X 2
2). Lelon -A701 (M) RGA 105c - 47uF, 50v x 3
3). Elite - L(0710) EL (M) 105c - 689uf, 16 X 2 (the one's I removed) C701 & 708 at top right hand corner.
4). Elite - L(0710) EL (M) 105c - 330uF, 35V X 4

I dont know which capacitors to order, like the OHM and Impedance or do I even have to worry about that as long as the Uf and Voltage match?
Thanks in advance.

[retiredcaps]

Re: Dell E172fpb

I dont know which capacitors to order, like the OHM and Impedance or do I even have to worry about that as long as the Uf and Voltage match?

1) PCBONEZ talks about the various parameters such as ESR, voltage, uF, etc at

https://www.badcaps.net/forum/showpo...30&postcount=7

2) I don't expect you to digest all the above, but if you want a "simple" choice of Panasonic caps, then PlainBill wrote a procedure on how to choose Panasonic FR, FM, and FC caps at

https://www.badcaps.net/forum/showpo...33&postcount=2

The Panasonic FR, FM, FC are likely to exceed the original cap specifications.

3) If you want a more streamlined approached, goto digikey.com. Try this.

a) Check the "in stock" box.
b) In the search field type in "470uF 25V FR". If it comes back successful, check the diameter and height to make sure they fit. Repeat for all other caps.
c) If the FR search was unsuccessful, try "470uF 25V FM". If that also fails, try "470uF 25V FC".

Basically your first choice is FR, then FM, and finally FC.

4) Capacitors die from age, heat, and shoddy build quality. Capacitors DO NOT have to be visibly bloated in order to bad. They can be out of tolerance uF (a 1000uF measures 20uF) and/or have high ESR (ohm). A multimeter will be insufficient to test for ESR. For that you need an ESR tester which costs between $50 and $300.

Most members here will recommend that you replace ALL capacitors except the largest one which rarely, but not never, fails.

[PlainBill]

Re: Dell E172fpb

One thing I would add. When ordering replacement caps, make sure they will fit. Measure the height and diameter of any of the original caps that are close together (diameter), and close to the cover. Make sure the replacements will fit.

From experience, it is embarrassing when you can't get the monitor back together because you ordered the wrong size cap.

PlainBill