LCD Desktop Monitor Fading to White, then Black

) =A0 =A0 =A0 =A0Length (mm)

(mm) =A0 =A0 =A0 Mouser

=A0 =A0 =A020 =A0 =A0 =A07 =A0 =A0 =A0 661-EKMQ451VN151MP40

..

=A024 =A0 =A0 =A05 =A0 =A0 =A0 5 =A0 =A0 =A0 667-ECA-1HHG470

..

22 =A0 =A0 =A010 =A0 =A0 =A05 =A0 =A0 =A0 667-EEU-FC1E681

..

22 =A0 =A0 =A010 =A0 =A0 =A05 =A0 =A0 =A0 667-EEU-FC1E681

..

24 =A0 =A0 =A010 =A0 =A0 =A05 =A0 =A0 =A0 598-361R821M025EG0E

..

24 =A0 =A0 =A010 =A0 =A0 =A05 =A0 =A0 =A0 598-361R821M025EG0E

..

24 =A0 =A0 =A010 =A0 =A0 =A05 =A0 =A0 =A0 667-EEU-FC1E331

..

Thanks for reviewing & the feedback. I'm glad I don't need to change the large cap.

I'm looking for a cap w/ a lower ESR for the C107 cap (47uF, 50V). I don't see 'ESR' in the data sheet. What do I look for? Would this one be better:

?

Most of these caps were near, if not at, the physical size limit. All of the 25V caps have

If the ESR isn't specified, then look for loss tangent or dissipation factor (tan sigma). Dissipation factor does NOT directly translate to ESR, but it's proportional when comparing caps at the same frequency. The lower number is better.

ESR = DF / (Pi * freq * C) You can calculate ESR, but there's a problem. The dissipation of the dielectric varies with frequency where the ESR number specified is only valid at the test frequency. When DF or loss tangents are specified, it's sometimes at 120Hz, where the capacitor is intended for a linear type AC power supply filter. When ESR is specified, it's usually at 100KHz which implies that it's for a switching power supply. The Panasonic EEU-FC series you included specifies ESR as impedance at 100KHz. For comparison, a 47uF/50v Panasonic EEU-FC series cap as below shows 0.6 ohms max ESR.

Well, for 47uf/50v the Panasonic EEU shows 0.15 DF. The previous Chemicon KMQ series cap shows 0.12 DF. I would call the Chemicon capacitor slightly better.

Unfortunately, the sanity check doesn't quite work. The ESR at 100KHz grinds out to: ESR = DF / (2Pi * freq * C) ESR = 0.15 / (6.28 * 0.1*10^6 * 47*10^-6) ESR = 0.15 / 29.8 = 0.0005 which is about 1000 times too small to be for real. When my brain recovers from this cold or flu, I'll try to figure out what I've done wrong. (I hate it when that happens).

Looking at the photos of the board, some of the caps look fairly tight. I guess you should probably leave it at 25V.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

saber850 wrote in news: snipped-for-privacy@37g2000yqm.googlegroups.com:

ESR Equivalent Series Resistance

ESR is usually NOT 'important' on new capacitors. One 'common' failure mode for electrolytic capacitors in an increase in ESR, especially in caps that have defective designs.

--
bz    	73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an 
infinite set.

..

Thanks for all the info.

Which tool(s) should I consider getting to help w/ the desoldering? I'm guessing there's something to help get the solder out of the PCB hole. Braided copper? Solder sucker?

Sigh. We're really down to the basics. You're probably dealing with RoHS solder. That means an 850F tip and a temperature controlled soldering iron. 750F will work, but takes a bit longer. I haven't looked at cheap soldering irons for a long time, so I don't have a specific recommendation. Note that if the soldering iron is rated only in watts, not temperature, go find something else. It's probably not temperature controlled.

I recently bought one of these conglomerations:

but haven't had a reason to use it yet. It looks big, clumsy, and has a rather large tip, but looks useful for some things. I don't think cleaning the pump is going to be fun while attached to a hot iron. We shall see.

Some kind of vacuum solder sucker should work:

Radio Shack also carries these. Lots more on eBay. Solder braid might also be handy, but not really necessary.

Most LCD power supply boards are single sided with no plated through holes. Those are the easiest boards to work with. When I recently replaced all the electrolytics on a Samsung LCD display (which didn't fix the problem), I just heated up the leads, and pulled on the capacitor case. No need for anything more elaborate. If the board was double sided or multi-layer, which have plated through holes, the solder sucker and solder wick would be needed.

If you haven't done much soldering, I suggest you practice with some scrap boards before attacking.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Solder suckers seem best suited for vacuum tube sockets and terminal strips. Solder Wick(tm) Seems best suited for lifting traces.

I've had extremely good luck using one of these:

Put the hole in the tip over the exposed lead, add a bit of solder then when it all melts, push the button on the vacuum and move the tool in a circular motion around the pin. Turn the vacuum off after you've removed the tool from the lead.

Occasionally, I get a lead stuck in the hole, but a simple chisel tip can get it free. Go back over, add solder and re- vacuum the hole to get it empty afterwards.

The key to ANY soldering operation whether it is assembly or desoldering is hot enough, fast and clean.

Of course, like the other Jeff I do this for a living, so investing in the correct tools is money well spent.

Jeff

--
?Egotism is the anesthetic that dulls the pain of stupidity.?
Frank Leahy, Head coach, Notre Dame 1941-1954

http://www.stay-connect.com

I just hate to agree with you, but you're right. Still, it is possible to remove components with either device if you're careful. However, for massive desoldering jobs, nothing beats a propane torch, air compressor, and blow gun.

Retch. I suffered with one of those for about a year at a former employer. About every 5 sucks, I had to clean the self clogging tip. There were about 5 of them in the lab and all of them clogged exactly the same way.

I switched to an overpriced Pace desoldering station and sucked happily ever after.

Big and ugly really is better.

Circular motion? Won't that tear up the pad? If I don't get all the solder in the first suck, I add some more solder and/or flux, get the joint hot, and suck again. Flux is the key as you can't suck dross. Moving the tip around the joint just seems to make a mess and more dross.

Yep.

Yep, yep, yep.

You call this living? I'm still agonizing over buying a hot air SMT desoldering station. I was borrowing one for a while and became addicted.

The other Jeff. (I haven't mailed the Symbol junk yet. Sorry.)

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

I like to think of it as "circling the drain". Obviously you don't press down on the pad, but I've found that doing this circular motion makes all the difference in the world sucking up enough solder to get an empty hole and exposed lead.

No rush.

Jeff

--
?Egotism is the anesthetic that dulls the pain of stupidity.?
Frank Leahy, Head coach, Notre Dame 1941-1954

http://www.stay-connect.com

..and don't have a big ground area, for me can even work a poor 25W iron.. maybe but depends on how big the board, to be sure start with a 50W one that comes much useful for other works like recapping pc mainboards.. i say only to save some money..

s

a good brand of low esr type. (105c)

er

Sanyo, Rubycon, Panasonic

ense-use,

safer and instructive

. but it is no so safe whitout

and face outside is more

So the "working" monitor stopped working today w/ the same symptoms. The only difference is that it has remained in this malfunctioning state all day--the longest I've ever experienced. I can't help but wonder if there's some truth to the theory that this is contagious. Fortunately, I ordered 2x the caps a couple days ago. So hopefully the problem is in fact the caps and I'll have both fixed soon.

I warned you. Unfortunately, this one good guess does not make up for all my other screwups.

This is the way rumors and religions are started.

Good move by planning ahead. What else can go wrong.... Well, work on one monitor at a time, so that you have the other board as a sample for which way to insert the capacitors, and where the connectors and screws are located. It should be easy (famous last assumptions).

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com               jeffl@cruzio.com
# http://www.LearnByDestroying.com               AE6KS

In article , saber850 writes

It'd be interesting to hear how you got on.

--
(\__/)   
(='.'=)  Bunny's thinking about giving Windows 7
(")_(")  a go despite what he's said about it...

Absolutely! I intend on posting back with my next steps.

At this point, I'm still waiting for the parts (currently expected to arrive tomorrow). I'll say I'm not thrilled to have paid >$8 to ship a 0.4lb package which takes 5 business days to arrive. Perhaps I'm spoiled by NewEgg's ship time & prices.

Fortunately, my monitors seem to be playing tag-team on functioning correctly, so I can still function at this point.

I just completed soldering all the new caps to one of the boards! For desoldering, I found it easier to simply heat each lead and gently pull the cap out. The braided copper didn't really help, perhaps because the pins are so small.

The good news is that the monitor functions fine (I thought I may have messed up one of the caps). The unfortunate news is that only time will tell if the problem is really solved.

I will post back with the status after a couple days. If all goes well, I'll repeat the procedure on the other board.

Thank you all for your help thus far!

So the "working" monitor stopped working today w/ the same symptoms.

------ what do you mean for 'working', them still had power boards swapped? A monitor can't contaminate anything, it's a stupid thought.. maybe your monitors are produced same day as them has been bopught same day and caps are equal and fails near same month or week.

ay

Before and after I had swapped the power boards, only one of the two monitors worked--and it contained the same power board each time.

Yes, both monitors were bought at the same time, and used roughly equally. But one monitor started failing over 18 months ago, while the other just started this month.

y

Bad news: the monitor w/ the new caps exhibited the same problem when I first powered it on this morning. Ugh...

Yes, both monitors were bought at the same time, and used roughly equally. But one monitor started failing over 18 months ago, while the other just started this month.

--- OK, the contamination doesn't exists then ... i'm sorry for your bad news.. i would to think to monitoring the pow.supply outputs and then evaluate if is a power board problem and which part of it, it is useful to know if want to buy an used or new board or continue to repair . If i'm not wrong the 12v line powers the inverter that by the video seems to work well, there is a 5v and nothing more or a 3,3v, test them, you can also supply 5v from another p.s.u. to have a verify. If 5v is stable there is maybe a transistor that powers the panel, it makes the on/off function for st.by mode, i have i Benq with this failed. you can test it, or test the supply pin to the panel, u need the datasheet of the panel for pinout, it is possible to make a bypass of this to supply the panel like i did for test.