Sun LCD (Samsung BR24CS) 24.1" - 2.3v Instead Of 6.2v Secondary

[fzabkar]

Re: Sun LCD (Samsung BR24CS) 24.1" - 2.3v Instead Of 6.2v Secondary

Fail it did, I put it aside. (My wife questioned this).

I replaced the capacitor from a circuit board I pulled out of a stove that recently fried on me. (Wife also wanted to know why I was keeping that).

Sounds like you might be a hoarder. Is your wife your therapist? :-)

[jgauthier]

Re: Sun LCD (Samsung BR24CS) 24.1" - 2.3v Instead Of 6.2v Secondary

Hello everyone!

This thread is 2 years old! But I thought it was valuable to share this. I have had this monitor since 2007. 8 years, and an amazing monitor it has been. I had some weird issues with it, and I knew it was going to fail. Fail it did, I put it aside. (My wife questioned this).

Today, I cracked it open and started probing around the power supply. I was also devoid of the promised 6.3v. However, my skill set did not lend me to figuring out why, but I knew enough to suspect a capacitor. Nothing was obvious. I found this thread, using some google-fu.

I replaced the capacitor from a circuit board I pulled out of a stove that recently fried on me. (Wife also wanted to know why I was keeping that). I change it with a 50v 47uF, and viola! POWER!

Even though I replaced the monitor, I am extremely excited to get this one back, as I love it!

Thanks everyone!

[avdocatwork]

Re: Sun LCD (Samsung BR24CS) 24.1" - 2.3v Instead Of 6.2v Secondary

Samsung LS24BRBAB-XAA with the same PSLF101401A Power Supply. I replaced the Caps in the following order to get the set running.

[misiu_mp]

Re: Sun LCD (Samsung BR24CS) 24.1" - 2.3v Instead Of 6.2v Secondary

Big thanks guys!
I found this nice looking 244t screen lying in the garbage. It showed no sign of life which was encouraging because power supplies are easier to fix than silicon logic. Replacing the obviously blown caps didn't help, but then I re-discovered this wonderful site with all the invaluable advice in it.
Indeed, replacing the standby transformer's startup capacitor brought life back to the machine and now it looks like I'm gonna have myself a nice screen for cheap!
I only had a 47uF at 50V but it did the trick. I attach some pictures to show where it is on the board.

[MdPhoenix]

Re: Sun LCD (Samsung BR24CS) 24.1" - 2.3v Instead Of 6.2v Secondary

I'd just like to add, even though this is over a year old. I have the same monitor in my basement with the same problem for a friend. After replacing all of the bad caps, and it wouldn't fire up, the startup cap was bad on mine as well. A little research goes a long way.

Thanks for a great repository of information!

[ryankam]

Re: Sun LCD (Samsung BR24CS) 24.1" - 2.3v Instead Of 6.2v Secondary

One of the most educational monitors I had was a 17" Gateway. The Lady who gave it to me said it wouldn't come out of sleep mode one day, so she unplugged it and plugged it in again, then she didn't get any power LED.

I pop it open, sure enough half the caps on the secondary are bulging. When I check the 5V line it's got a slight 'twitch'. So I replace all the 'important' caps in the secondary. Plug it in, still no power, still the same twitch. After a great deal of searching I came across a reference to a 47uF, 50 volt cap - the startup cap. Replaced that, and away it went.

Now when someone insists on changing only the obviously bad caps, I just grin at the problems they will be having.

PlainBill

Hahah Very well said. My hats off to you. We now share the same pain! And knowledge. Thanks again buddy!

[PlainBill]

Re: Sun LCD (Samsung BR24CS) 24.1" - 2.3v Instead Of 6.2v Secondary

Customer tells me he got some caps from ebay and some laying around the house. Hahaha. Never trust the CUSTOMER!

One of the most educational monitors I had was a 17" Gateway. The Lady who gave it to me said it wouldn't come out of sleep mode one day, so she unplugged it and plugged it in again, then she didn't get any power LED.

I pop it open, sure enough half the caps on the secondary are bulging. When I check the 5V line it's got a slight 'twitch'. So I replace all the 'important' caps in the secondary. Plug it in, still no power, still the same twitch. After a great deal of searching I came across a reference to a 47uF, 50 volt cap - the startup cap. Replaced that, and away it went.

Now when someone insists on changing only the obviously bad caps, I just grin at the problems they will be having.

PlainBill

[ryankam]

Re: Sun LCD (Samsung BR24CS) 24.1" - 2.3v Instead Of 6.2v Secondary

Hmm, I would not have suspected caps since they were "all replaced" in post #1 and then AGAIN in post #17.

Customer tells me he got some caps from ebay and some laying around the house. Hahaha. Never trust the CUSTOMER!

[ryankam]

Re: Sun LCD (Samsung BR24CS) 24.1" - 2.3v Instead Of 6.2v Secondary

Definitely unusual, since you say that ALL the caps were previously replaced. Even if the replacement cap wasn't a low-esr one, I would expect it to work long enough, for testing purposes, to power on the supply. So, the original 10uf cap went bad and was replaced by another cap that apparently also didn't work and you got it to work by using a 22uf cap?

Yes the 22uf cap worked fine. I guess it has nothing to do with timing so the uF wasn't to important. Yea I never trust a customer word when they say I did xyz so I just redid the board one by one starting with that startup cap and hit it on the head.

[ryankam]

Re: Sun LCD (Samsung BR24CS) 24.1" - Repair Success - Thanks Guys!

This IS a strange one, I've never seen it before. There is a startup cap on every SMPS controller. If it's bad, usually you see nothing but a pulsing output. I've never seen one where you got a steady, but very low, output voltage.

Anyway, glad you got it working.

PlainBill

The odd thing is both power supplies had the exact same bad cap. Customer said he replaced all caps but I think he did not. But come caps on the board were capxon and the replaced ones were samxon. The startup one was samxon but I double customer touched it. Anyway on one power supply I got 11.25 V and no power at all on the secondary side. The other was giving 11.50v and giving 2.62v on the secondary. So there certainly is a fragile balance. Thanks again guys.

[jetadm123]

Re: Sun LCD (Samsung BR24CS) 24.1" - 2.3v Instead Of 6.2v Secondary

Hmm, I would not have suspected caps since they were "all replaced" in post #1 and then AGAIN in post #17.

Oops! I missed post #17. So, that means the startup cap was replaced 3 times?!

[retiredcaps]

Re: Sun LCD (Samsung BR24CS) 24.1" - 2.3v Instead Of 6.2v Secondary

Definitely unusual, since you say that ALL the caps were previously replaced.

Hmm, I would not have suspected caps since they were "all replaced" in post #1 and then AGAIN in post #17.

[jetadm123]

Re: Sun LCD (Samsung BR24CS) 24.1" - 2.3v Instead Of 6.2v Secondary

Definitely unusual, since you say that ALL the caps were previously replaced. Even if the replacement cap wasn't a low-esr one, I would expect it to work long enough, for testing purposes, to power on the supply. So, the original 10uf cap went bad and was replaced by another cap that apparently also didn't work and you got it to work by using a 22uf cap?

[PlainBill]

Re: Sun LCD (Samsung BR24CS) 24.1" - Repair Success - Thanks Guys!

Hey Everyone,
Thank you for your input. I remember reading a post by I believe plainbill a while ago where he stated that the startup capacitor for the standby transformer may be bad but not visibly. I was getting 11.50V on the Q that was saying it should get 12V before it turns on and hands over power. I thought the 11.50V was enough or close enough. I said you know what let me change that 50V/10uF cap out and put this 50V/22uF cap in here and see what happens. I did this on the primary side of the power supply. I instantly tested the secondary side and got the 6.23V I was supposed to get. Boom! Plugged it in, powered it up, and now I am writing an invoice for the customer and raving over here. Thanks a million you guys. PlainBill you are a legend. Period! When you had mentioned to me voltage was being brought down by possibly caps. I removed caps on the secondary side and never thought of them causing voltage drop on the primary side. So on a hunch I removed that cap I mentioned, plugged that sucker in, and boom. We are in business. Thanks again guys I will surely be posting more success stories soon im sure.

Ryan - RNK Computers and Electronics

This IS a strange one, I've never seen it before. There is a startup cap on every SMPS controller. If it's bad, usually you see nothing but a pulsing output. I've never seen one where you got a steady, but very low, output voltage.

Anyway, glad you got it working.

PlainBill

[ryankam]

Re: Sun LCD (Samsung BR24CS) 24.1" - Repair Success - Thanks Guys!

Hey Everyone,
Thank you for your input. I remember reading a post by I believe plainbill a while ago where he stated that the startup capacitor for the standby transformer may be bad but not visibly. I was getting 11.50V on the Q that was saying it should get 12V before it turns on and hands over power. I thought the 11.50V was enough or close enough. I said you know what let me change that 50V/10uF cap out and put this 50V/22uF cap in here and see what happens. I did this on the primary side of the power supply. I instantly tested the secondary side and got the 6.23V I was supposed to get. Boom! Plugged it in, powered it up, and now I am writing an invoice for the customer and raving over here. Thanks a million you guys. PlainBill you are a legend. Period! When you had mentioned to me voltage was being brought down by possibly caps. I removed caps on the secondary side and never thought of them causing voltage drop on the primary side. So on a hunch I removed that cap I mentioned, plugged that sucker in, and boom. We are in business. Thanks again guys I will surely be posting more success stories soon im sure.

Ryan - RNK Computers and Electronics

[ryankam]

Re: Sun LCD (Samsung BR24CS) 24.1" - 2.3v Instead Of 6.2v Secondary

OK Update. Here are some new pics. Also I removed caps one by one and the voltage kept rising. The highest I got was 3.98V I notice as I connect it back to the logic board it drops to 2.6v again. I believe that drop is so it can achieve the 5v since it says it gives off 6.2V. Not sure. Anyhow I have included detailed pics. Please let me know what you may think. Thanks plain bill again. Also I have replaced all caps again on this board. Not just ones customer changed.

[ryankam]

Re: Sun LCD (Samsung BR24CS) 24.1" - 2.3v Instead Of 6.2v Secondary

It's a very unusual problem. And I can't think of many likely causes. Let me explain a little bit of how these work.

You have already noticed that there are three main boards to this monitor - the power supply, the signal board, and the inverter. The power supply is a dual supply. There is the standby section, which is always on whenever the monitor is plugged in. That usually powers the entire signal card; the signal card draws relatively little power. When the signal card detects a video signal (or when it is turned on by the power button, or when it first receives power) it sends a control signal back to the power supply. That signal turns on the main supply and the PFC front end. The main supply powers the inverter and possibly the LCD panel.

Both sections of the power supply (standby and main) are relatively simple. By design, they offer excellent regulation of the output voltage. This involves feeding the actual output voltage back to the controller IC. About the only reasons for a low output are really bad capacitors, a failure in the output voltage sensor / feedback loop, or excessive load.

One thing to try is to operate the power supply disconnected from the signal board. The main supply won't turn on, but the standby section will. With no load, the output voltage should be stable and correct. If the output is correct when by itself, but drops with the signal card hooked up, it points to either excessive load or bad caps.

Good pictures are essential to assisting in troubleshooting. Saying 'Check the current sense resistor' doesn't help much unless you already know which resistor it is, or I can tell you which it is.

PlainBill

Very good bill. I do understand to that standpoint how they work. I should have been more clear in explaining that the power was tested for secondary power with nothing connected to it but the wall plug. So there was no load at all. There is one 2200uf cap the customer did not change. I highly doubt that one cap is causing all this trouble but then again there are many ghosts in the machine. I Am going to post a few highdef pics just to see if you can see anything im missing. I am going to remove the one cap the customer forgot on the secondary side and see if that raises any voltages.

[PlainBill]

Re: Sun LCD (Samsung BR24CS) 24.1" - 2.3v Instead Of 6.2v Secondary

I didnt know he asked for it he just said it was not so good a pic. Ill do that when I am home in the AM. I posted their voltage ratings but ill get the pic.

What I was hoping for was if someone knew a common reason why something that is normally supposed to be at a certain voltage is 4 volts lower than what it's supposed to be. Is it common for bad caps to pull down voltage, or for bad fets to do so. Or maybe a resistor outta range. I tested all resistors though.

It's a very unusual problem. And I can't think of many likely causes. Let me explain a little bit of how these work.

You have already noticed that there are three main boards to this monitor - the power supply, the signal board, and the inverter. The power supply is a dual supply. There is the standby section, which is always on whenever the monitor is plugged in. That usually powers the entire signal card; the signal card draws relatively little power. When the signal card detects a video signal (or when it is turned on by the power button, or when it first receives power) it sends a control signal back to the power supply. That signal turns on the main supply and the PFC front end. The main supply powers the inverter and possibly the LCD panel.

Both sections of the power supply (standby and main) are relatively simple. By design, they offer excellent regulation of the output voltage. This involves feeding the actual output voltage back to the controller IC. About the only reasons for a low output are really bad capacitors, a failure in the output voltage sensor / feedback loop, or excessive load.

One thing to try is to operate the power supply disconnected from the signal board. The main supply won't turn on, but the standby section will. With no load, the output voltage should be stable and correct. If the output is correct when by itself, but drops with the signal card hooked up, it points to either excessive load or bad caps.

Good pictures are essential to assisting in troubleshooting. Saying 'Check the current sense resistor' doesn't help much unless you already know which resistor it is, or I can tell you which it is.

PlainBill

[ryankam]

Re: Sun LCD (Samsung BR24CS) 24.1" - 2.3v Instead Of 6.2v Secondary

See PlainBill's post #9 asking for a clear focused picture of the connectors so we can see the legends.

I didnt know he asked for it he just said it was not so good a pic. Ill do that when I am home in the AM. I posted their voltage ratings but ill get the pic.

What I was hoping for was if someone knew a common reason why something that is normally supposed to be at a certain voltage is 4 volts lower than what it's supposed to be. Is it common for bad caps to pull down voltage, or for bad fets to do so. Or maybe a resistor outta range. I tested all resistors though.

[retiredcaps]

Re: Sun LCD (Samsung BR24CS) 24.1" - 2.3v Instead Of 6.2v Secondary

See PlainBill's post #9 asking for a clear focused picture of the connectors so we can see the legends.