Samsung 931BF, the infamous "two seconds to black" problem.

[29a]

Hello.

So my 931BF has the typical "two seconds to black" problem. On a rare ocassion, the backlight will stay on if i power cycle it alot of times, but this takes time and there's a scary buzzing sound coming from inside the monitor and the backlight flickers. Every time i turn it on, the inverter transformer makes a really weird short noise that resembles the sound of a moving laser inside a cdrom. This short noise from the inverter is always heard, even if i disconnect the CCFL's. There's also some constant hiss coming from the yellow transformer. So far i have tried blindly replacing all the caps and the inverter transformer. The problem persists. The original caps were C(r)apXon's. Almost all the caps are replaced with new ones except the 22uf/50V which i salvaged from an old but perfectly working stereo. Also, one 330uf/25V cap is left unchanged since i didn't have enough caps. I did try replacing it with a new 470uf/25V but it didn't make a difference. The biggest cap is also left unchanged. I also blindly replaced the inverter transformer with a new one bought on ebay. I ran continuity tests on the F101 and F202 fuses, the are both closed. I have very little EE knowledge and experience but i can use a solder and i do have a DMM. I never measured anything on a powered on circuit.

I don't know what to do next so any advice is very appreciated.

Here are some pictures of the board.

http://img231.imagevenue.com/img.php...A_122_57lo.jpg
http://img151.imagevenue.com/img.php..._122_194lo.jpg
http://img297.imagevenue.com/img.php..._122_547lo.jpg
http://img287.imagevenue.com/img.php...8_122_79lo.jpg

[jsog]

Re: Samsung 931BF, the infamous "two seconds to black" problem.

That it stays on once in a while could still be a capacitor problem. Were the replacements low ESR? It could also be a CCFL going bad, which may not be practical to fix.

The 22uF from a stereo would have a different problem. It's probably only rated for 85 degrees C, not 105.

[mariushm]

Re: Samsung 931BF, the infamous "two seconds to black" problem.

Is the big capacitor swollen in the second picture or is it just my eyes playing tricks?

Just yesterday someone was complaining his monitor was buzzing and it turned out his big capacitor was swollen as well.

[Th3_uN1Qu3]

Re: Samsung 931BF, the infamous "two seconds to black" problem.

Is the big capacitor swollen in the second picture or is it just my eyes playing tricks?

Considering it's the exact same type of cap, it's likely. It could just be glue tho, can't tell from this angle... but if the big cap is bloated, here's your replacement: http://search.digikey.com/scripts/Dk...me=565-1481-ND

[29a]

Re: Samsung 931BF, the infamous "two seconds to black" problem.

Here are more pictures of the big cap.

http://img203.imagevenue.com/img.php..._122_545lo.jpg
http://img296.imagevenue.com/img.php..._122_171lo.jpg

The replacement caps mostly came from a lcd repair kit bought on ebay. I accidentally ordered the wrong kit so i only half of them were usable on my power supply. These are Luxon and Nichicon branded. I got the missing ones from a local electronic repair guy. These are KSC branded. And yes, the 22uf is rated for 85 degrees.

[jsog]

Re: Samsung 931BF, the infamous "two seconds to black" problem.

Well, it isn't swollen. But only an ESR meter will really tell if it's still working.

Luxon... not a good brand. Never heard of KSC, might or might not be a problem. It's the low ESR that's important.

The last picture shows a United Chemicon (I think) SME series, which is 85 degree and not low ESR, either. The label looks weird. Counterfeit?

The 22uF is probably a startup cap, it can cause this problem. Use something good, like this or this.

[29a]

Re: Samsung 931BF, the infamous "two seconds to black" problem.

Actually, there's only a single Nichicon and a single Luxon. The Luxon is a 330uf/25V 312B(M). Nichicon is 1000uf/25V H9523. 47uf/64V is an Antel, no series markings. The KSC ones have no series markings. One 470uf, the one closest to the inverter is SME branded and rated at 85 degrees. the other two 470uf are KSC's.

[jsog]

Re: Samsung 931BF, the infamous "two seconds to black" problem.

Nichicon should have a two-letter series code. The one in the last picture has the UCC/Chemi-con shield logo, and SME is the series. The printing matches some UCC caps I have, so never mind. It's real SME, but the SME series isn't low-ESR.

[29a]

Re: Samsung 931BF, the infamous "two seconds to black" problem.

Ok, things just got weird. I replaced two 470uf KSC capacitors with original CapXon ones since i can't find specs for the KSC capacitors (KSC == KINGSUN ELECTRONIC). And the backlight came to life. It works, there's no backlight flicker, but there's a nasty, very irritating hiss coming from the power supply. The weirdest thing is that it only works if i remove this aluminum plate. Here's a picture.

http://img186.imagevenue.com/img.php..._122_499lo.jpg

Original capacitor set is a mixture of capXon KF and KM series.
Right now, 47uf, 22uf, 1000uf and a single 470uf are replaced and the rest of them are original capXon ones. The replaced 470uf is rated as low esr and is currently replaced with a KSC cap.

[Th3_uN1Qu3]

Re: Samsung 931BF, the infamous "two seconds to black" problem.

A power supply operating on the edge can behave in many funny ways. My recommendation is to replace all C(r)apxon capacitors with good quality ones like Rubycon, Samxon or Nichicon. The capacitors you have bought are obviously not adequate.

[lti]

Re: Samsung 931BF, the infamous "two seconds to black" problem.

Your image host sucks as well. It displayed an ad over the entire image, and the X in the corner of the ad did not close the ad. Instead, it opened a fake porn site that was designed to do nothing but steal your identity and infect your computer.

[Th3_uN1Qu3]

Re: Samsung 931BF, the infamous "two seconds to black" problem.

I have Fanboy's Adblock List. Maybe you should too.

[PlainBill]

Re: Samsung 931BF, the infamous "two seconds to black" problem.

Your image host sucks as well. It displayed an ad over the entire image, and the X in the corner of the ad did not close the ad. Instead, it opened a fake porn site that was designed to do nothing but steal your identity and infect your computer.

Which brings us to several things which have not been mentioned.

1. It is STRONGLY suggested that all pictures be attached to the post by using 'Manage Attachments' - below the text entry area.

2. Hosting images on this forum means the picture will always be available.

3. Experiences like Iti's and similar events is the reason I will not view pictures hosted off-site. Others feel the same way.

PlainBill

[29a]

Re: Samsung 931BF, the infamous "two seconds to black" problem.

My apologies for my choice of the image hoster. I am not aware of the ads since Adblock blocks almost all of them. I will reupload the pictures.

I have also noticed that the lower part of the lcd panel is dimmer than the upper part.

[PlainBill]

Re: Samsung 931BF, the infamous "two seconds to black" problem.

My apologies for my choice of the image hoster. I am not aware of the ads since Adblock blocks almost all of them. I will reupload the pictures.

I have also noticed that the lower part of the lcd panel is dimmer than the upper part.

Those are excellent pictures (OK, the first one suffers from camera glare). I hope to be able to read component identifiers; on these I can almost read the resistor's values!!

I'll confirm what others are saying. The best approach is to use name brand low ESR caps. In particular, the small (22-100uF) caps can cause weird behavior.

If you still have 'two seconds to black' after replacing the caps, the most likely cause is is the CCFLs or the wiring to the CCFLs.

PlainBill

[Duke7213]

Re: Samsung 931BF, the infamous "two seconds to black" problem.

My monitor would stay on at first for about 20 minutes then shut off. The problem gradually got worse and the monitor would no longer stay on for more than a few seconds. I thought for sure it needed new caps so I bought a cap kit. I removed the power supply and visually inspected the capacitors and they appeared to be fine. I figured one must still be bad but I took a closer look (with a magnifying glass) at the board looking for weak solder joints. Sure enough, I counted 12 joints that had the infamous solder "ring" indicating the joints that had gone bad. I used a fine tip soldering iron and touched them all up. The monitor has been working flawlessly for over a month! I should have replaced the capacitors while I had it apart but I'm good to go for now. Bad solder joints may be something to consider with your monitors.

Duke7213

[Behemot]

Re: Samsung 931BF, the infamous "two seconds to black" problem.

Got this model with 2 secs to black, the diode turned off as well so it wen't to short protection I think. After complete recap now I see image for two secs, than it goes to black, but diode is still on and when I toggle the SOURCE button, I see image for 2 secs every time.

Any idea? All semiconductors I tried seemed fine, inverter transformer measures ~1250 and 1650 ohms.

[Behemot]

Re: Samsung 931BF, the infamous "two seconds to black" problem.

Resoldered most of the colder-joint looking joints, nothing. Problem seems to be in the inverter area. Without CCFLs it's OK, with different CCFLs I get the same problems. There is double transistor AP4525GEH which however does not seem to be opened to me. Do you think it may be bad transformer? It shows 1227 and 1594 ohms after resoldering on it's secondary. Seems still as a too high difference to me.

[retiredcaps]

Re: Samsung 931BF, the infamous "two seconds to black" problem.

inverter transformer measures ~1250 and 1650 ohms.

The difference between the 2 should be less than 3%.

If you have TMS91365CT, the suggested resistance is around 950 ohms as per

http://lcdparts.net/TransformerDetai...ProductID=3715

Replacement on ebay for $6.50 USD + free shipping.

http://www.ebay.com/itm/150706207569

[Behemot]

Re: Samsung 931BF, the infamous "two seconds to black" problem.

There's TMS91429CT. Found these for 1,88 USD only http://www.ebay.com/itm/1-pcs-Invert...item5d3c907bc4 so I guess I will take a few