Dell E172fpb

[cadillacman]

Re: Dell E172fpb

hmm.. looks like im measuring 140ohms across the center and third leg of the little "2sc" transistors everyone is talking about. Time to pull them and see if i have an odd man out. Im hoping i have one shorted compared to the rest, at least i will know thats what it is. A repair kit on feebay for only like $8 so , if i find my odd duck out i will order that kit. The caps visual check ok but i know that doesent mean mean much.

[cadillacman]

Re: Dell E172fpb

Ugh. nevermind. Stepped out of my car tonight after work, monitor disassembled in a bag. Shit the car door, prosseded to slip and slide all over some nasty slick ice, and broke the heck out of the lcd. Ugh.

Oh well. At least i have parts for the next one i suppose.

[doorynrun]

Re: Dell E172fpb

Hello All,
I'm new to this forum. I joined a couple of weeks ago to better understand what it might take to repair a Dell e172fpb I'm trying to save from the landfill.

It started out as a 2 Seconds To Black problem that was traced to a couple of '5707s being shorted. After getting a transistor/fet/fuse repair kit from eBay it then started doing the Power Light Flashing mode, so I got a replacement cap kit from eBay. Really there was only one obvious cap failure, one of the 1000mf @ 10V ones...but what the heck put them all in.

I've finally discovered the true nature of the problem: a bad CCFL. It took a while, but I noticed arching along the edge of the LCD panel. After disassembling the panel I could see a burn marks at the end one of the tubes.

It looks like CCFL-Warehouse has the lamp assemblies for $35 or so. I haven't decided yet to put out the cash. It's really not worth it, but the inverter and digital boards are in good shape. Is there any interest in anyone buying these boards?
--Cheers!

[selldoor]

Re: Dell E172fpb

On old ccfls there will always be some burn marks - Sometimes it just needs rewired and the insulation improved - got to be worth a try.

PM cadillacman see if after his crash he has any bulbs.?

[doorynrun]

Re: Dell E172fpb

On old ccfls there will always be some burn marks - Sometimes it just needs rewired and the insulation improved - got to be worth a try.

Thanks for the tip! It made me re-think the situation and try more troubleshooting. Now that the CCFLs are out of the case, bench-testing is easier to see what's really happening. Only one set of lamps tries to fire; but exchanging them between connectors on the inverter/ps board, both try to fire. I should say here I'm back to the Power Button flashing mode. Connector CN753 which would connect to the lower CCFL is not producing HV.

So, back to the drawing board and try to figure out why that section is causing an overload shutdown.
--Cheers!

[selldoor]

Re: Dell E172fpb

You may need to recheck your 5707s again. I dont think you have said if you resoldered everything big on the board. A poster recently did all that you did only to have his 5707s go again.
I will try and find the post and add it in for you to read.


Here you dont need to read all the thread - life is too short
just the last few posts. (Some Benqs and dells are similar)

https://www.badcaps.net/forum/showthread.php?t=4304

[doorynrun]

Re: Dell E172fpb

Thanks again SellDoor,
You are right, life is too short! But, I have gone over this thread as well as a similar Benq 17" thread. There I located a good schematic of the ps/inverter board. But, I have yet to go over re-soldering the board. I've been over it with magnifying glasses and the solder side "looks" OK. But it won't hurt retouching it a bit. Also, I've decided to go ahead and get the rest of the electrolytic caps changed. Let's see how it goes!

[selldoor]

Re: Dell E172fpb

Resoldering should be FIRST. Retouching a bit will not do it - you need to remove the old solder and re apply fresh. Did you re test your 5707s.

[doorynrun]

Re: Dell E172fpb

I have checked them in-circuit with my DMM set to diode mode. I'm comparing my readings with the matching pair.
You make a good point about resoldering. I ordered some additional Solder-Wick with my caps from Digi-Key. I will take your advice!
One other observation I'd like to relay from a little earlier in the troubleshooting phase was that I removed the pico fuse to see if the +5 and +3.3 supplies would stabilize. With the inverter circuitry connected and the power button flashing on/off I measured fluctuations on +5 and +3.3 that followed the flashing.
As you can guess, removing the pico fuse allowed the 5/3.3V supplies to remain solid and the power button on/off function actually worked.
Looking at the schematic it looks like there's no feedback coming from the inverter supply. So why would component faults on that side of the pico fuse have any effect on +5/+3.3? I can only guess that something like a shorted N5707 causing a large current demand in the inverter supply would cause some disruption to +5/+3.3 and send a feedback pulse to shut the whole front end of the SMPS down?
Well I may not have an exactly perfect schematic; and I apologize for not digging up a reference to it.

I'll work on the resoldering job first and theory second. --Cheers!!

[doorynrun]

Re: Dell E172fpb

Here's the link to the Benq schematic; I think it bears a very close resemblance to what I've got:
https://www.badcaps.net/forum/showth...enq+17&page=15
It's attached to Post #299

Also, thanks for not asking for good close-ups of the board. I can get them to this forum soon!

[doorynrun]

Re: Dell E172fpb

I'm happy to report my E172fpb is working again! I'm very sure SellDoor's advice about resoldering the board did the trick. I did get the other electrolytic caps on the PS board replaced. I decided to not replace the caps on the digital board.

BUT, I'm somewhat embarrassed to report I was not careful about mounting the two 5707's located towards the edge of the PC board and one or both collector tabs we touching the case causing an overload. They were sitting too high; I was thinking it would help the airflow. I'm lucky they didn't short out!!

It took me a bit to try and get it working outside of the case where I could get to measuring places on the circuit board. Then things started to make sense. Well, I guess we'll see how long the repair will last. I don't have too much need for an analog input LCD, but it's nice to have a spare and get this one fixed!

SellDoor, thanks again for your support!!

[226BWytics]

Re: Dell E172fpb

Hi guys,

My Dell E172fpb died on me this week after more than 10+ years of service. With your help, i will hopefully extend its lifetime a while longer. I am a noob with electronics, i have replaced some badcaps here and there but that's about it. The monitor works for 2 seconds and then goes black with the LED flashing in orange.

I checked the PCB and saw that one of the trannies (Q760) was completely burnt. Dockarl suggested 10 years ago to use D44H8 as a replacement for the trannies, but i dunno if that information is obsolete and there are better options now. Clearly i am getting the Q760 replaced, but i am still figuring out if there are any other good candidates for replacement given that im gona get my hands dirty. From what i read in this thread, some people had problems with other trannies and caps. I have some idea of which caps i should be replacing from some posts and some pictures from a repair kit i found in amazon:

https://www.amazon.com/Repair-E172FP.../dp/B006FE35VQ

but i am not sure if replacing anything else is recommended. Btw, would getting the repair kit be a good idea or is it better to get my parts from a major distributor (i.e. RS)? Should i desolder parts and test them with a multimeter to check further what i should replace?

I am a bit lost

Cheers.

Edit: I forgot to mention that some of the caps are really close to the PCB and i dunno if its because they are bulging from the bottom or just really pushed into the board.

[boyebaran]

Re: Dell E172fpb

Hi
you must check CCfl before getting repair kit.

[226BWytics]

Re: Dell E172fpb

Hi again,

I checked the ccfl's and the wires are pretty well attached to the tubes. Could you walk me through testing them with the PCB? I don't own one of those lab PSU's to test them out.

Cheers.

[stj]

Re: Dell E172fpb

i would replace *all* the electrolytics other than the big 400v one with panasonic FR first on a monitor that age.
including the small ones on the video board - that fixes 80% of problems just doing that.

[226BWytics]

Re: Dell E172fpb

Yeah, i will probably do that. I also have to replace the burnt transistor, what would you recommend as a replacement for that?

Cheers.

[stj]

Re: Dell E172fpb

no idea.
someone who has worked that model should answer

[226BWytics]

Re: Dell E172fpb

Hi again,

I replaced the transistor and some known to fail caps but the problem still persists.

When you suggested me to replace also the small electrolytics, you meant only the ones from the video card (i understand that is the small PCB) or from both cards? On the biggest card, counting the little ones, there are easily 30 caps, replacing all of them feels like an overkill.

Cheers.

[stj]

Re: Dell E172fpb

30? got a foto?

[226BWytics]

Re: Dell E172fpb

Here :
http://m.imgur.com/a/0B0FP
http://imgur.com/a/IAT1b