Samsung 2253BW replaced caps and fuse still broken :(

[darkphreekquency]

Ok so I have a Samsung 2253bw that died on me the other day. I woke it up from sleeping and it flickered once and went black (as in the back-lights went out) I can see an image if I shine a light into the monitor. I opened it up and found 4 domed up caps on the power board. I replaced the bad caps (820uf 25v 105c) x 4 then tested. Still getting a solid power light and no back-lights (slight hum coming from inverter when plugged in).

Took it apart again and did some more research to find out about the small green pico fuse on the board which in my case was 4 amps. I couldn't find one around so I replaced it with a glass fuse (also 4amps 125v) soldered to some leads. It is set on the board away from everything and is not shorting on anything at all. I also decided to replace the 2 1000uf 16v caps on the board and the 1 330uf 10v (replaced with a 330uf 25v) I ordered the caps from Digikey. Now the monitor does something different. As soon as it is plugged in you can here an intermittent clicking from the power board and the power button does nothing. No power light at all.

It seems like this happened after replacing the fuse. My guess it that there is another problem here and when the fuse was replaced it is now evident. Im surprised replacing the blown caps didn't just fix it. Any ideas? I have videos but there just on my computer at the moment I can take a few pics of the board if its needed.

Is there anyone that knows the exact sequence of events pretty much that takes place upon inserting the power cable? there is one cap i did not replace near the power button connector but when the fuse was the pico fuse (blown) the power lights worked fine and I could push the button and see an image on the screen (with no backlights) . .. really sorry for the long post and it is my first so I apologize if I didn't include what i needed to I tried to be thorough I am just frustrated. I frequently repair small electronics so I am no stranger to a soldering iron all my contacts are solid (tested with a multimeter)

Any help at all id really appreciate it. This site is amazing thank you all for all you have contributed

[PlainBill]

Re: Samsung 2253BW replaced caps and fuse still broken

Classic description of a short on one of the power supply outputs. Go over your soldering, check the orientation of the caps you installed (you wouldn't be the first to put a cap in backwards), and if you don't find any problems lift the fuse you installed.

There is one other possibility - there is a small (10 -100uF, 50V) cap near the smps transformer. If that is bad it will create the same symptoms, but I' check for a short first.

PlainBill

[darkphreekquency]

Re: Samsung 2253BW replaced caps and fuse still broken

Thank you so much for responding so quickly, this is my personal monitor and its killing me not having it as I am a 3d designer. went over everything with a multimeter to make sure my cap connections were good. they are all in the correct direction. Im looking through all my parts for another 50v 47uf cap ... surprising its not in the 2 power supplies I have. Ive got a whole slew of motherboards to and nothing even close . I get continuity on the fuse even at remote locations and the small pico fuse is just the same as a glass fuse correct? just smaller and cheaper? The pico fuse has no continuity so I figured that was it when I tested it. You think the only other things could be that cap? Its not domed at all but im sure like with other things it could be bad without a visible sign. I wish I had capacitance on my meter

[PlainBill]

Re: Samsung 2253BW replaced caps and fuse still broken

Thank you so much for responding so quickly, this is my personal monitor and its killing me not having it as I am a 3d designer. went over everything with a multimeter to make sure my cap connections were good. they are all in the correct direction. Im looking through all my parts for another 50v 47uf cap ... surprising its not in the 2 power supplies I have. Ive got a whole slew of motherboards to and nothing even close . I get continuity on the fuse even at remote locations and the small pico fuse is just the same as a glass fuse correct? just smaller and cheaper? The pico fuse has no continuity so I figured that was it when I tested it. You think the only other things could be that cap? Its not domed at all but im sure like with other things it could be bad without a visible sign. I wish I had capacitance on my meter

There are two likely explanations for the 'clicking'. Both depend on the SMPS design used in virtually every monitor.

In a nutshell, the startup cap (47uF, 50V in this case) is charged through a high resistance until it reaches the startup threshold for the SMPS controller, typically 12 volts. The smps controller starts driving the power FET, producing voltage pulses on the outputs of the secondary AND on a tertiary winding. This tertiary winding provides run power for the SMPS controller.

The clicking occurs if the voltage across the startup cap drops below the run threshold of the SMPS controller before the power from the tertiary winding can maintain it. The two usual causes of this are an excessive load (short) on the output of the power supply, or a defective startup cap.

Before you start tearing apart something to find a suitable cap, let's eliminate other possibilities. With the power supply disconnected from the signal card, what is the resistance from each DC output to ground? What happens if you disconnect the fuse you used as a replacement for the picofuse?

(There is nothing wrong with using a glass fuse, but you have not established the reason the picofuse blew.)

Also, pictures REALLy help.

PlainBill

[darkphreekquency]

Re: Samsung 2253BW replaced caps and fuse still broken

Here are some pictures Im not sure where the dc outputs would be is that where the 4 cables to the backlights connect? and I Would just test the resistance to ground? I am a bit confused but im going to pullt he fuse now just wanted to get some pictures up

[darkphreekquency]

Re: Samsung 2253BW replaced caps and fuse still broken

Pictures

[darkphreekquency]

Re: Samsung 2253BW replaced caps and fuse still broken

Ok so with the fuse removed as soon as i plug it in a hear a feint high pitch whining. When I push the power button the light comes on and the noise goes goes away (this is all with the 4 leads to the lights removed). That start-up cap maybe?

[darkphreekquency]

Re: Samsung 2253BW replaced caps and fuse still broken

ok so i replaced the start-up cap with another one from a new power supply ( I have a ton of them and most are outdated and have low output) and I put back the fuse. now I am getting a much faster clicking from the board and the power button does nothing like before. Sorry for posting so much im not impatient or anything just trying to be as informative as possible

[PlainBill]

Re: Samsung 2253BW replaced caps and fuse still broken

ok so i replaced the start-up cap with another one from a new power supply ( I have a ton of them and most are outdated and have low output) and I put back the fuse. now I am getting a much faster clicking from the board and the power button does nothing like before. Sorry for posting so much im not impatient or anything just trying to be as informative as possible

Well, the results from lifting the fuse is pretty definitive. The problem lies in the inverter. The picture of the top is quite good, but the one of the bottom of the board isn't, so I will have to improvise.

The inverter controller is the 24 pin IC; the drivers are the two 8 pin ICs. What are the part numbers of the drivers?

You might as well put the original starup cap back in; it's not the cause of your problems.

PlainBill

[darkphreekquency]

Re: Samsung 2253BW replaced caps and fuse still broken

no writting on the small chips or maybe it burned off big IC is sem2006 0749

[darkphreekquency]

Re: Samsung 2253BW replaced caps and fuse still broken

here is a closer pic. There is a scratch on the pcb. I was really concerned but it didn't destroy the trace. I have a crazy cat that likes to jump on my shoulders when im doing things that are important lol.

[alexanna]

Re: Samsung 2253BW replaced caps and fuse still broken

https://www.badcaps.net/forum/showth...ghlight=2253bw
Wonder if the 8 pin ICs are the same as in the above thread post # 12

[PlainBill]

Re: Samsung 2253BW replaced caps and fuse still broken

here is a closer pic. There is a scratch on the pcb. I was really concerned but it didn't destroy the trace. I have a crazy cat that likes to jump on my shoulders when im doing things that are important lol.

Explain to the cat that such behavior is unacceptable. Then lock it in another room.

Alexanna's suggestion seems to be correct - these ICs (dual transistors) are very probably STM8309 or equivalent. But rather than just ordering, let's test them.

Since you are the type of person who puts up with a disruptive cat, I'll assume the worst. Wikipedia has the numbering for the package. The package contains two transistors. Pins 1, 2, and 7&8 are one transistor; pins 3, 4, and 5&6 are the other. Set your DMM on the 200 ohms range and measure the resistance between pins 1 and 2; between 1 and 7&8; and between 7&8 and 2 (& means you can use either pin 7 or 8). Do the same for pins 3, 4, and 5&6. Then do the same for the other package.

The criteria are simple - if you measure less than 20 ohms between any pin combination I listed, the IC is bad. If one is bad, replace both. As mentioned in the other thread, they are available on eBay, but I suspect equivalent packages are available from other vendors.

Now go let the cat out.

PlainBill

[darkphreekquency]

Re: Samsung 2253BW replaced caps and fuse still broken

This cat is just a nut. Hes a climber and loves to jump up on people shoulders and hang out. I just need to get a large dog lol, looks like you guys are right and the 1 IC is bad im getting around 1 ohm on some of the tests. After some digging I ordered the 2 IC's that were mentioned in the other thread. It looks like the same board design so I imagine those are correct. They look a little crispy too I bet that's why I cant see the part # any more. Any tips for soldering stuff so small? (other than tying the cat up haha)

Thank you guys so much. I looked at that thread before but I didn't see the part about the inverter drivers. I appreciate the help. Hopefully I get them installed alright and we are a go. This project has kind of been more of a first time LCD learning experience than a cost effective repair at this point. I shouldn't have shipped the CAPS 2 day USPS

[PlainBill]

Re: Samsung 2253BW replaced caps and fuse still broken

This cat is just a nut. Hes a climber and loves to jump up on people shoulders and hang out. I just need to get a large dog lol, looks like you guys are right and the 1 IC is bad im getting around 1 ohm on some of the tests. After some digging I ordered the 2 IC's that were mentioned in the other thread. It looks like the same board design so I imagine those are correct. They look a little crispy too I bet that's why I cant see the part # any more. Any tips for soldering stuff so small? (other than tying the cat up haha)

Thank you guys so much. I looked at that thread before but I didn't see the part about the inverter drivers. I appreciate the help. Hopefully I get them installed alright and we are a go. This project has kind of been more of a first time LCD learning experience than a cost effective repair at this point. I shouldn't have shipped the CAPS 2 day USPS

Get a Border Collie as playmate for the cat.

There are several youtube videos on soldering SMD parts. I suggest using ChipQuik to remove them, solder braid to clean up the board, then apply a little flux to the board to hold the new IC in place. Nudge it into position, solder one corner, then solder the other corner, then do the rest of the pins. I use a 27 watt iron, it's easy.

PlainBill

[alexanna]

Re: Samsung 2253BW replaced caps and fuse still broken

The first surface mount multiple pin IC ,I remember as being very scary.
ChipQuik really makes removal a snap, Be careful some of the ICs are glued in place so don't force removal.
As PlainBill recommended use Flux to hold the chip in place.
I have had the best luck using a rosin-core solder,Melt some solder on the tip of your iron and starting at the solder pad draw a line dragging the solder to the pin.
If for some reason you bridge two pins together,Apply some flux to the bridge and with the help of solder braid drag the solder from between the two pins.

[mariushm]

Re: Samsung 2253BW replaced caps and fuse still broken

See this video: http://www.youtube.com/watch?v=fYz5nIHH0iY and this one : http://www.youtube.com/watch?v=b9FC9fAlfQE

It shows several methods of soldering stuff, including ICs with lots of pins. The second one shows surface mount soldering in particular but both are very informative.

[darkphreekquency]

Re: Samsung 2253BW replaced caps and fuse still broken

thank you all for the tips. Ive been soldering for quite some time now ( I think I was 8 when I first melted some wires together incorrectly lol) I was probably 14 or so before I really understood how to do it properly and im 28 now. Ive never tried surface mount stuff before so Ill have to get some chipquick and/or practice on some other stuff I have here. Watched some vids on chipquick though and I really couldn't imagine not using it. Ill post again when I get these chips in (supposedly the 6th) It would be so nice if Radioshack actually carried one useful component. Every time I need something its just never there. Last time I went I was looking for a simple 7805 5v regulator and there was an assorted bag of LED's where they were supposed to be. LED holders, a million different sizes and colors, Project boxes to stick all your LED's. I must admit I do love light but seriously there are other things people need haha.

sorry for the rant

[PlainBill]

Re: Samsung 2253BW replaced caps and fuse still broken

I understand the rant. The problem is Radio Shack makes more money selling someone a scanner, stereo, or DVD player than they do selling overpriced components. So they don't carry useful parts in hope that people will decide to buy a scanner, stereo, or DVD player instead.

PlainBill

[AkosLukacs]

Re: Samsung 2253BW replaced caps and fuse still broken

Hi everybody.

Don't want to open a new thread, since i have the same monitor, and the attached pictures of the boards look pretty much like mine. Hope it's not a problem.

So, my case: no backlight, but otherwise working electronics => replaced four caps, the fuse, and seems to be working again. Just powered it for a short time, since had no 4A fuse, temporarily just used a piece of wire...

My question: Four caps were visibly bulged, and replaced those.
(look @ the pictures in #6 for cap position)
Two on the left side, close to the output transformers, blue in the picture, and originally in my monitor are 25V/820uF SAMWHA XC 105°C caps. (can't find a datasheet for these)
Two on the right side, right above the mains transformer, also blue in the picture, and originally 25V/820uF SAMWHA WB 105°C caps. Although the datasheet doesn't list 820uF ones...

But can't find a (hungarian) supplier with suitable 820uF ones in stock, and no 820uF caps in my drawers either, so used Rubycon YXG caps: 25YXG1000M 1000uF/25V 105°C ESR=0.035ohm caps.

What do you think? Would it be OK, to use the monitor with these caps, 1000uF instead of original 820uF?

Thanks.