Dell E171FP saved ... almost ... well maybe

[chevelle_nut]

I took in a Dell E171FP 17" the other day. Top half black screen, lower half white screen. Then no picture at all, just the 'ol orange light.

I pull it apart and visually find swollen lytic on the inverter board. Phew an easy one for a change, so I thought. I swap the cap on the inverter and check voltages. I got 7.59v on what I suspect is the 12v rail and 4.16v on the 5v rail. So I now figure something is pulling the supply down, so I disconnect the AD board (that also feeds the seperate inverter board) and the ps is now at 12v and 5v.I disconnect the inverter and try just the p.s. and the AD board, still back to 7.59/4.16.

At this point, maybe the supply is not really good as it pulls down with just the AD load, no real signs of heating up on the AD just low voltages. I google around and see "repair kits" listed - they replace the 6 CapXon filter caps on the power supply. Maybe choppy power causing my woes. I replace the (2) 2200uf@10v and (1)470uf@25v and the (3) 1000@25v and power it up, same 7.59/4.16.

So now I look at the AD board again and start sizing up the sm 'lytics and a couple of thru hole caps as well. I lay out all I have in stock and swap as many out as I can with what I have at arms length. Still no improvement in voltages. As a last ditch effort I reconnect the inverter , plug in the ccfl's and the power switch cable. Power it up and wooohooo!!! it works, I can see the dell self test blah blah blah. So power down and connect video source, tah dah picture perfect. I check the 5v/12v supply when the unit is powered on and they are right on the money 5.03v/12.18v. As soon as the power button is hit they go back to 7.59/4.16... grrrrr. I feel like I was chasing a ghost.

Happy ending ? NO. Seems the 2200uf caps I had in stock are 16v and are about 3/16" too tall and are now preventing me from reassembling this unit. So here is my question, the 5v rail filter consists of (2) 2200uf@10v and (1)470uf@25v all in parallel can I replace the combined 4870uf worth of caps with (3) 1500uf @16v I have in stock? seems like it would be close enough for horseshoes or hand grenades. Also, can someone shed some light on why there is a 25v rated cap with the 2 larger 10v ones? Especially confusing as all of this is on the 5v line anyway.

Oh, btw the 5v on the power supply I think is just for standby power/on off functions. The AD board has a 5v regulator on it that runs off the 12 supply. Even with the low input power condition 7.59v it still managed 5.03v @ the regulator out.

[chevelle_nut]

Re: Dell E171FP saved ... almost ... well maybe

I'll post pics and list of caps I replaced in the morning. Things are getting blurry now too much rosin fumes I suspect.

[jetadm123]

Re: Dell E171FP saved ... almost ... well maybe

If you go with your current idea and this is filtering for the 5V rail, then I think 4500uf vs the original 4870uf is way too low. Any chance you have a spare 470uf that you can parallel (if it fits) with one of the 1500uf? At least you'll be over by 100uf. Of couse, there's no guarantee that this will work either.

As for the 25V cap, you may want to double check to make sure it's on the 5V rail and not the 12V one. If it's on the 5V rail, then maybe that was the only thing available at the time that would fit.

[pedro]

Re: Dell E171FP saved ... almost ... well maybe

4500uF vs 4870uF is no drama for me, especially while you are chasing another issue - it is well inside the usual +/- 10% or 20%.

You indicated no heating observed on the video board when the 5/12V rails are pulled down. That suggests to me that the PSU isn't handling load at all well (i.e. poor regulation). Check that the main filter cap voltage doesn't droop when the video board is present. If that's OK I'd be looking into the SMPS feedback area, and I'd use a CRO (if you have one) on both these areas. Beware the grounded_CRO-live_target when looking at the main cap.

[chevelle_nut]

Re: Dell E171FP saved ... almost ... well maybe

4500uF vs 4870uF is no drama for me, especially while you are chasing another issue - it is well inside the usual +/- 10% or 20%.

You indicated no heating observed on the video board when the 5/12V rails are pulled down. That suggests to me that the PSU isn't handling load at all well (i.e. poor regulation). Check that the main filter cap voltage doesn't droop when the video board is present. If that's OK I'd be looking into the SMPS feedback area, and I'd use a CRO (if you have one) on both these areas. Beware the grounded_CRO-live_target when looking at the main cap.

I was thinking my 3 Rubycon MBZ's are probably closer than those CapXon's ever were to being spec. I was referring to the no heat up issue on the AD board because I was thinking something should be giving off heat if it is pulling the rails down. Now I am not sure if they actually DO get pulled down or just sit idle until the power button is pushed. When the unit is in the "ON" condition, the rails come right up to 5v and 12v. I was checking them in the "OFF" state, and I kept chasing problem because I thought the rails needed to be at full voltage, even when off. I guess I was wrong. The unit works great as it sits right now, with the non-fitting 2200's. I am going to swap out those this morning and try the 1500's in all 3 locations.

[Th3_uN1Qu3]

Re: Dell E171FP saved ... almost ... well maybe

The only rail that might be present in standby will be the 5v (logic) rail. But not even that is a rule - i just fixed a 22" Horizon yesterday and it shut down both 5v and 12v when it went into standby. It probably had a "5vsb" ala PC power supplies.

[chevelle_nut]

Re: Dell E171FP saved ... almost ... well maybe

No joy, 4500uf gives me just the orange light. <sniff>

I am going to pull the last 1500uf out and wrap the legs of the 470uf@25 I had in there with another 1500uf like Jetadm123 suggested. I have some real estate on that side I could maybe eek something into. Maybe 4970uf works...

<fingers crossed>

[chevelle_nut]

Dell E171FP saved... YESSSSSS!!!!!

Gold star to jetadm123 !!! You nailed it, I was figuring the 10% would be close enough given the tolerances but 4500 did not cut it.

I added the 470uf that was in my original replacement group to bump up the total to 4970uf albeit 100uf more than original and 470uf more than my first try, it is working like a champ ! I am letting it burn in right now but so far I neither see nor smell smoke (and that's good, right?).

Those Samsung guys have some seriously good calculators. It is amazing that they can build stuff with junk caps and make it just last long enough to get through the warranty period. Don't get me wrong though, if it weren't for the junk caps we'd have little to talk about here... just a thought.

I need a few moments for the coffee to kick in then I'll start uploading the pics.

[Th3_uN1Qu3]

Re: Dell E171FP saved ... almost ... well maybe

They probably run the thing at the maximum voltage ripple allowed by the picture processor... That's why even a single bad cap usually makes a monitor unable to start. And those junk caps probably won't be dead if they were installed in an area with less heat, or if they stopped doing nonsense like installing 25v general purpose caps in place of 16v low-ESR ones.

[smason]

Re: Dell E171FP saved... YESSSSSS!!!!!

Gold star to jetadm123 !!! You nailed it, I was figuring the 10% would be close enough given the tolerances but 4500 did not cut it.

I added the 470uf that was in my original replacement group to bump up the total to 4970uf albeit 100uf more than original and 470uf more than my first try, it is working like a champ !

<Spock> Fascinating</Spock>

It would be very interesting to see scope screenshots of the ripple with the 2 different capacitance values.

[pedro]

Re: Dell E171FP saved... YESSSSSS!!!!!

Gold star to jetadm123 !!! You nailed it, I was figuring the 10% would be close enough given the tolerances but 4500 did not cut it.

Assuming your 4500 really was 4500, that is almost in the unbelievable category - less than 10% drop in capacitance changed the result, when cap tolerances are greater than that. How could they accommodate (in production) cases where caps all came in at -10%?

I added the 470uf that was in my original replacement group to bump up the total to 4970uf albeit 100uf more than original and 470uf more than my first try, it is working like a champ ! I am letting it burn in right now but so far I neither see nor smell smoke (and that's good, right?).

Those Samsung guys have some seriously good calculators. It is amazing that they can build stuff with junk caps and make it just last long enough to get through the warranty period. Don't get me wrong though, if it weren't for the junk caps we'd have little to talk about here... just a thought.

Samsung!! Did somebody say Samsung?

[chevelle_nut]

Re: Dell E171FP saved ... almost ... well maybe

Here are the pics:
First picture swollen cap on inverter
Second is original group of power supply - nothing visually bad (just CapXon on the label)
Third is new caps in final configuration (3) 1500uf@16v + 470uf@25v on the 5v rail, (3) 1000@16v on 12v rail.
I did not get a full picture of the AD board but after recap but you can see some of the radials sticking up in the last shot. Those are 100uf@16v one was an sm the other thru-hole. I also replaced a few 10uf@10v.

PlainBill what app do you use for marking up photos? I have a pre-op picture of AD board I can mark up to show the other caps I replaced.

[jetadm123]

Re: Dell E171FP saved ... almost ... well maybe

Glad it worked out! Another monitor saved from the landfill!

[PlainBill]

Re: Dell E171FP saved ... almost ... well maybe

Here are the pics:
First picture swollen cap on inverter
Second is original group of power supply - nothing visually bad (just CapXon on the label)
Third is new caps in final configuration (3) 1500uf@16v + 470uf@25v on the 5v rail, (3) 1000@16v on 12v rail.
I did not get a full picture of the AD board but after recap but you can see some of the radials sticking up in the last shot. Those are 100uf@16v one was an sm the other thru-hole. I also replaced a few 10uf@10v.

PlainBill what app do you use for marking up photos? I have a pre-op picture of AD board I can mark up to show the other caps I replaced.

I use the Yugo of photo marking software - MS Paint.

PlainBill