Samsung Syncmaster 245BW

[zachn]

Hi, I have 4 of these monitors all of which do not power up the inverter. I have read this tread and check all the problem component listed, all tested ok. My problem however is I am only getting 8v where 24v should be. I am stumped. Does anyone have other suggestions of faulty components that would cause this problem?

[retiredcaps]

Originally Posted by zachn

My problem however is I am only getting 8v where 24v should be. I am stumped. Does anyone have other suggestions of faulty components that would cause this problem?

1) You could have bad caps on the secondary side. If you are only getting 8V, check the 470uF 35V or higher rated caps. Caps don't have to be swollen or bloated to be bad. They could be out of uF capacitance or have high ESR (ohms).

2) The Schottky diode could be bad? Measure the DC voltage at the Schottky diode to see if you get 24V or more.

3) Post pictures so we can make suggestions. Post clear focused pictures after reading

http://www.badcaps.net/forum/showthread.php?t=1868

4) Please do not post pictures inline.

5) Take your boards to a window on a sunny day, turn flash off, and use macro mode. Take a top down view of all your boards (front and back). Make sure the photo is legible so that we can read the PCB printing clearly. A shutter speed of 1/125 or faster will produce nice clear focus pictures. Try to get a photo that is 2000x2000 resolution or as close as possible.

Here is an example of the pictures we want.

http://www.badcaps.net/forum/showpos...94&postcount=1

[zachn]

The pics would be the same as the pics at the start of this thread. I have tested the caps with a fluke 177 and all the caps seem to be with in the range of error. Can I test the ESR just with the regular ohms check? Or would I need another testing tool?

Also the voltages in the 24v controller chip are good and one monitor I have seems to have an intermittent 8v error, but I have yet to narrow down the problem.

[retiredcaps]

Originally Posted by zachn

Can I test the ESR just with the regular ohms check?

You need an ESR tester to test for ESR.

[zachn]

I believe the problem is the semiconductor at position ZDTM851. The part number is KIA431A. Does anyone know where buy a replacement part on the internet?

[PlainBill]

Originally Posted by zachn

I believe the problem is the semiconductor at position ZDTM851. The part number is KIA431A. Does anyone know where buy a replacement part on the internet?

First, compare the part you have to this datasheet. If they match, you can buy the TL431A from a number of sources, including eBay, Digikey, Mouser, and just about any reputable electronics distributor. Google TL431A

PlainBill

[jackherer]

This is a very informative thread, thanks to everyone involved.

I found RB805 to be open circuit on my 245b, I replaced it and it has been operating fine for over 72 hours so far.

[zachn]

Originally Posted by PlainBill

First, compare the part you have to this datasheet. If they match, you can buy the TL431A from a number of sources, including eBay, Digikey, Mouser, and just about any reputable electronics distributor. Google TL431A

PlainBill

I replaced the KIA431A with new TL431AIZ and monitors are working now with a good 24v.

unfortunately, when i powered up one the monitors the screen was cracked. do you know of a good replacement or supplier for that part. i have the screen out but cant seem to find a good part number on it.

[Slang]

Hi
very good thread indeed.
But i still haven't been able to repair my 245B.
Symptoms: no 24 and no 5.3 V: standby voltage (5.2 V) ok; 68 ohms resistances are ok; nothing wrong with capacitors.
I tried to replace F9222L but no luck.
In power supply schematics posted some time ago there are two point marked B and M and in this points (in schematics, if i have understood) i should find 292V.
In my board, in these points i read 360V/370V. Anyone can explain?

I tested voltages present at pins of TDA4863G and all is as in the schematics but not on pin 5 (0.9V instead of 1.1V) and pin 7 (0.4V instead of 0.48V).

Also tested voltages at F9222L and found these voltages:
pin 4: about 0
pin 7: 19.36
pin 10: 4.97
pin 11: 4.60
pin 12: 4.97
pin 13: 3.04
pin 14: 0.70
pin 15: 2.69
pin 16: 0.00
pin 23: 390

All voltages measured with monitor ON (blu light on on power button).
There are problems on pin 11, 14, 15 and 16.

Still not tried QM802 (BQ in my board) exchange.

Can you better address my research?

Tia
Slang

[Slang]

PS: forgive my english

[PlainBill]

Originally Posted by Slang

PS: forgive my english

You English is not a problem. I'm sure I would do much worse with your language.

The higher voltage (360 instead of 292) is best explained by a working PFC circuit and should be considered normal, at least for the time being. Other demands on my time prevent me from fully studying the problem and suggesting test points, but there is no reason you can't do this. I would suggest the following approach.

The power supply has two sections, a standby supply which is always on, and a main supply which is switched on whenever the monitor is 'On'. For some reason the main supply is not turning on.

There is a control line from the logic card back to the power supply. It drives an opto-isolator, which turns on the SMPS controller (the F9222L) for the main supply.

There are two possibilities.

1. When this line goes active the main supply starts, 5.3V and 24V come up, but the logic card turns the control line off again.

2. When this line goes active the main supply fails to start.

The test is to check the outputs of the main supply and see if there is any sign of activity when the Power button is pressed. If there is none, see if the control signal actually reaches the F9222L.

PlainBill

[Slang]

Hi
thank you Bill for your answer.
No sign of voltages when i switch on the monitor.
All tests were done with lamps connected to the inverter but lcd panel disconnected : is this a right situation to make all tests or there are problems if i don't connect the lcd panel (i have many problems to take some measurements if i make all connections).
I changed BQ transistor (with BR: 2sc2412) but no improvements.
Thank you again.
Slang

[bermudahonk]

Hello guys,
I also posess a 245b without 24V. After looking around an taking measurements I only found that the resistor RB813 has no rings and is completly black. From a scematic attached by Zeha it should have a value of 1.5 Ohms. Can someone confirm this? You can find the resistor nearby TB810S. The resistor is not smelling burned, but it's odd to me that the body i just black. I'm reading 1.2 Ohms
Thanks in advance.
My readings on the F9222L (no 24V, blue light on):

Pin 04: 0V
Pin 07: 19,2V
Pin 10: 4,95V
Pin 11: 4,62V
Pin 12: 4,95V
Pin 13: 3,03V
Pin 14: 0,72V
Pin 15: 4,93V
Pin 16: 0V
Pin 19: 339V
Pin 20: jumping around 660V
Pin 23: 393V

[PlainBill]

Let's try working through this logically. I've attached a picture of the bottom of the power supply. Note the area outlined in blue. That contains the control line for the main power supply. Unfortunately the contrast is poor, and I can't trace the signal path.

Step 1. Using the Gnd pins within the blue area, do either S_B or PSON change voltage when the front panel power button is pushed?

Step 2. Above the area I circled is a long white label. Above that are the words 'HOT" and 'DC380V'. And above those are the solder pads for two leads. Understand what those mean - there is 380 VDC across those points. That is more than enough to give you a painful jolt, so BE CAREFUL!!!

The left one of these appears to be ground. Use that as the reference (ground) point for the following test. Back at the area in blue note PC802S. That appears to couple the control signal for the power supply. Does either of the two right hand pins of PC802S change voltage when the Power button on the front panel is pressed?

If they do, I will need better pictures of that area.

PlainBill

[bermudahonk]

Hi,
I provided some better photos. In my case I measured the QM802 and althought it should be a npn transistor from my readings I would guess it's a pnp transistor. So I think I should replace it.
I'm from germany . I would be glad for some pointers on where to get the replacement. So far I just found shops which only sell huge amounts.

[bonney]

http://obrazki.elektroda.net/73_1280397270.jpg
Drawing of PSU

[bonney]

http://obrazki.elektroda.net/22_1280397270.png
and F9923L

[Slang]

Originally Posted by bermudahonk

Hello guys,
I also posess a 245b without 24V. After looking around an taking measurements I only found that the resistor RB813 has no rings and is completly black. From a scematic attached by Zeha it should have a value of 1.5 Ohms. Can someone confirm this? You can find the resistor nearby TB810S. The resistor is not smelling burned, but it's odd to me that the body i just black. I'm reading 1.2 Ohms

Yes, mine is the same.

Thanks in advance.
My readings on the F9222L (no 24V, blue light on):

Pin 04: 0V
Pin 07: 19,2V
Pin 10: 4,95V
Pin 11: 4,62V
Pin 12: 4,95V
Pin 13: 3,03V
Pin 14: 0,72V
Pin 15: 4,93V
Pin 16: 0V
Pin 19: 339V
Pin 20: jumping around 660V
Pin 23: 393V

You are nearly im my same situation (my redaing on pin 15 is 2.70 but all other eradings match).

Slang

[bermudahonk]

Hello,
since no one has answered yet, I did the tests. In my case, I don't have 24V.

Originally Posted by PlainBill

Let's try working through this logically. I've attached a picture of the bottom of the power supply. Note the area outlined in blue. That contains the control line for the main power supply. Unfortunately the contrast is poor, and I can't trace the signal path.

Step 1. Using the Gnd pins within the blue area, do either S_B or PSON change voltage when the front panel power button is pushed?

Yes they do. Standby is (as the name indicates) always at 5,2V. PSON shows 0V when the power button is off and about 3,6V when ist on (blue light).

Originally Posted by PlainBill

Step 2. Above the area I circled is a long white label. Above that are the words 'HOT" and 'DC380V'. And above those are the solder pads for two leads. Understand what those mean - there is 380 VDC across those points. That is more than enough to give you a painful jolt, so BE CAREFUL!!!

The left one of these appears to be ground. Use that as the reference (ground) point for the following test. Back at the area in blue note PC802S. That appears to couple the control signal for the power supply. Does either of the two right hand pins of PC802S change voltage when the Power button on the front panel is pressed?

Althought there are no marks on that picture i just followed your instuctions. When the power button is off there ist just around 30V sitting on the bottom pin. When power button is on (blue light) there is also 30V on the upper one.

Originally Posted by PlainBill

If they do, I will need better pictures of that area.

PlainBill

In a few hours from now I will provide a macro shot of this area. I just need daylight.

I hope I could help.
Soon I will get two more broken TFTs. I'd be glad to find a solution. I'm still checking. After reviewing my results I have to corect my previous remark about tne QM802. I confused emitter, collector and base. The transistor seems to be OK.

[PlainBill]

Originally Posted by bermudahonk

Hello,
since no one has answered yet, I did the tests. In my case, I don't have 24V.


Yes they do. Standby is (as the name indicates) always at 5,2V. PSON shows 0V when the power button is off and about 3,6V when ist on (blue light).

Althought there are no marks on that picture i just followed your instuctions. When the power button is off there ist just around 30V sitting on the bottom pin. When power button is on (blue light) there is also 30V on the upper one.
In a few hours from now I will provide a macro shot of this area. I just need daylight.

I hope I could help.
Soon I will get two more broken TFTs. I'd be glad to find a solution. I'm still checking. After reviewing my results I have to corect my previous remark about tne QM802. I confused emitter, collector and base. The transistor seems to be OK.

Good work. No further pictures are necessary, thanks to bonney who provided a schematic.

In an earlier post you asked about RB813. The measurements you made, the function of the resistor (current sensing) , and the fact that the standby supply is working indicates the resistor is good. Not all resistors have color bands.

I'm going to have to study the data sheet extensively to determine the meaning of the various voltages.

PlainBill