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

[ryankam]

Hello All,
I have a power supply from this monitor that is giving me only 2.3V instead of the 6.2V listed on the board secondary. All the caps were replaced by the customer so I have no clue what the original sizes or voltages should have been but he said he kept all the voltages the same or increased them and the uF were the same so I have to take his word for it. Anyhow the PWM is a FSDM0565RB and I did some voltage tests on it but am not sure if that would determine if anything was shorted or not. I get 11.23v on the VCC pin and 1V on the Vfb pin. The main cap gives me 167V and I have checked all fuses. Bridge Rectifiers are fine. Varistors/Thermistors seem ok. Just stumpped as to why the secondary would not give me full power. I suspect the FSDM0565RB is the cause but not sure or if there is a bad resistor/ cap somewhere. I have no esr meter to test caps but like I said they are replaced. The resistors and diodes are all within specs. I only tested the ones within the vacinity of the PWM and near the Main power and all seem fine. Any input would be great. Board says it is a kinari24 which I cant find anywhere.

[retiredcaps]

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

We always want to see clear focused pictures of the boards using the manage attachments (see my sig file below) so we know what we are dealing with and can suggest test points.

[ryankam]

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

Thanks retired caps you had to give me about 30 more seconds the server kept telling me there was a security token error contact admin. I just resized images and now it works. Haha!

[seanc]

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

If the customer replaced the caps, then why does that still look like the factory glue still all over them?

[ryankam]

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

If you notice the glue has two points of contact. One is supposed to be on the cap the other is on what ever else. The glue is not touching any of the caps, they just didnt remove it. Any technical information is helpful. Thanks though sean.

[ryankam]

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

If the customer replaced the caps, then why does that still look like the factory glue still all over them?

Looks are deceiving in pictures.

I found a model number for the board: pslf101401a

[seanc]

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

Google says that PSU is in a Samsung 244T

[retiredcaps]

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

The main cap gives me 167V

1) On larger sized monitors, there are usually two power supplies. One is the 5V standby, and the other is the normal SMPS with optional PFC.

2) Please attach a picture of the logic board.

3) Please verify that 5V DC standby is present and showing steady voltage.

4) List any voltages on the logic card connector. In particular, see if the voltage regulators are working properly. If the voltage regulator is part number AL1117-33, the suffix, implies the output voltage. In this example, it would be 3.3V DC.

5) If this SMPS has a PFC, the voltage across the main cap should be around the 300V DC range.

[PlainBill]

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

Definitely a dual supply, and it looks like a PFC front end may be present.

Two questions come to mind.

1. What caps (brand and series) were used as replacements?

2. The picture of the bottom of the power supply is useless, the top is much better, but still falls a little short. There appear to be two output connectors. Are the pins of those connectors labeled? 6.2V is an unusual output voltage.

PlainBill

[ryankam]

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

Google says that PSU is in a Samsung 244T

hey sean thanks again. I looked at that monitor on google and it looks dead onto the monitor I have. But this one is branded SUN. So thanks now I know where I can find another supply if this is bad to the point of no repair. Thanks bud.

[ryankam]

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

SeanC - The logic board says 244T on it by the way I just noticed it.

1) On larger sized monitors, there are usually two power supplies. One is the 5V standby, and the other is the normal SMPS with optional PFC.

--Just one in this monitor. I have only seen two in plasma tv's.

2) Please attach a picture of the logic board.

--- Pic of logic attached and pic of power/logic attached. This is all thats under the hood besides inverter and tcon.

3) Please verify that 5V DC standby is present and showing steady voltage.
--- I wish I could get the 5V DC but that is the whole problem I am not getting 5 I am supposed to get 6.2 according to the board markings but I get around 2.3V.


4) List any voltages on the logic card connector. In particular, see if the voltage regulators are working properly. If the voltage regulator is part number AL1117-33, the suffix, implies the output voltage. In this example, it would be 3.3V DC.
---Voltage Reg is: 1501-33. I tested all pins to ground. 0.00V. But I expected this since im getting nothing from secondary.


5) If this SMPS has a PFC, the voltage across the main cap should be around the 300V DC range.

-158.2 is across main cap.

[ryankam]

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

Definitely a dual supply, and it looks like a PFC front end may be present.

Two questions come to mind.

1. What caps (brand and series) were used as replacements?
--Caps Are Samxon 35v 1000uf caps. The main one which the user did not see popping is capxon and there is one more capxon that looks to have not been replaced.

2. The picture of the bottom of the power supply is useless, the top is much better, but still falls a little short. There appear to be two output connectors. Are the pins of those connectors labeled? 6.2V is an unusual output voltage.
--Ya I only put the bottom of the supply because I see others post that way sometimes I always thought it was useless too. If need be I can get out the big boy and take a highdef pic. But I dont know if there servers can handle that. It was already giving me trouble uploading with an iphone pic. I agree 6.2v is odd but there is a sticker on the top of a covered transformer that reads:
24V 3A
13V .5A
5.4V 3.5A
6.2V 1.0

And that 6.2v is on the 3 pin (Only get 2.62V) connector which reads. On/off | Gnd | 6.2V

The other large connector looks like it is just passing voltage over to the inverter throught the logic board.And that is where the 13V/24V/5V writings are on the board.


PlainBill

sss

[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.

[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.

[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

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.

[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" - 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

[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

[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?