Samsung Syncmaster 245BW

[kmoonen]

Hi There

I have a Samsung Syncmaster 245BW, I have 8,96 volts coming from the 24 volts that powers the inverter. Black Screen, blue power light turns the power on and off, but no backlight...

Ken

[retiredcaps]

Re: Samsung Syncmaster 245BW

See the instructions below on how to post top down view pictures of your boards. Please follow the instructions below exactly.

The cause of your low voltage (9V) could be bad caps.

[Toasty]

Re: Samsung Syncmaster 245BW

Welcome!

There are several threads involving this display. Use the search for 245BW.

Please identify the part numbers for the power supply board and inverter. BN44-???? etc.

Toast

[kmoonen]

Re: Samsung Syncmaster 245BW

Here are the pictures . all of the caps on the entire board were replaced, and rechecked to make sure all were correct, as well as the 3 resistors that commonly are a problem (RB805, RB806 and RB807)

[retiredcaps]

Re: Samsung Syncmaster 245BW

1) What brand and series are the replacement caps?

2) What is the DC voltage across the legs of CM851 and CM852?

3) Just above CM851 and CM852 are two diodes mounted on heatsinks. What are the DC voltage on these diodes?

4) CN803 shows a legend with 5 pins marked as 24V DC. Are these pins showing 24V DC?

5) If you disconnect the inverter board from the power supply board, does CN803 measure 24V DC?

[alexanna]

Re: Samsung Syncmaster 245BW

1) What brand and series are the replacement caps?

2) What is the DC voltage across the legs of CM851 and CM852?

3) Just above CM851 and CM852 are two diodes mounted on heatsinks. What are the DC voltage on these diodes?

4) CN803 shows a legend with 5 pins marked as 24V DC. Are these pins showing 24V DC?

5) If you disconnect the inverter board from the power supply board, does CN803 measure 24V DC?

Don't forget to see retiredcaps above post.
Here is another thing you can check, if my memory is correct the capacitor I have circled in red is a known failure item and if it is bad you will have stand by voltage but you will lose the 24v rail.
Chances are you will see no obvious failure, but if you remove it from the board you may notice slight burning on the pins.

[kmoonen]

Re: Samsung Syncmaster 245BW

I will get aound to getting all those reading a little later today .. I do have voltage across the 24v , but it is only 8.6 volts...
even with the inverter disconnected still 8.6 volts

[kmoonen]

Re: Samsung Syncmaster 245BW

How do i measure the voltage of the 2 diodes ?.

[retiredcaps]

Re: Samsung Syncmaster 245BW

How do i measure the voltage of the 2 diodes ?.

It is most likely a 3 pin diode that looks like this

-><-

Put your black probe on a ground screw. Put your red probe on the middle pin. You should get a DC voltage reading.

[kmoonen]

Re: Samsung Syncmaster 245BW

8.12VDC , And 8.10VDC

[retiredcaps]

Re: Samsung Syncmaster 245BW

8.12VDC , And 8.10VDC

Hmm, that is really low. Just to verify we are looking at the right diodes ...

1) What are the part numbers for both?

2) What are the cap ratings for CM851 and CM852?

I was expecting the DC voltages at the diodes to be slightly higher than 24 V DC.

[kmoonen]

Re: Samsung Syncmaster 245BW

FCH20U10 for both Diodes
Both Caps 35V 1000uF

[retiredcaps]

Re: Samsung Syncmaster 245BW

This took some research, but thanks to zeha in the mega 245BW thread, I found his schematic in post

https://www.badcaps.net/forum/showpo...&postcount=326

I zoomed into the appropriate section and posted it here.

Now, I'm not very good at reading schematics, but FCH20U10 is directly getting its feed from the transformer. So if it is 8.x V DC there, then that leads me to think one or more of the following:

1) The TM801S transformer is bad. Rare, but not impossible.
2) Both FCH20U10 are bad. Two diodes bad at the same time? Maybe not.
3) F9222L might not be working 100% and causing the primary side to misbehave?

In his pdf schematic, it shows the expected voltages for F9222L. Compare it with your lcd. Pin 23 is the interesting one.

[retiredcaps]

Re: Samsung Syncmaster 245BW

PS. Warning high voltage alert. Note pin 23 is 392V DC.

[Toasty]

Re: Samsung Syncmaster 245BW

Can you answer the model number questions and the caps brand/series questions please?

What is the voltage across the mains cap in standby vs. on?

[PlainBill]

Re: Samsung Syncmaster 245BW

This took some research, but thanks to zeha in the mega 245BW thread, I found his schematic in post

https://www.badcaps.net/forum/showpo...&postcount=326

I zoomed into the appropriate section and posted it here.

Now, I'm not very good at reading schematics, but FCH20U10 is directly getting its feed from the transformer. So if it is 8.x V DC there, then that leads me to think one or more of the following:

1) The TM801S transformer is bad. Rare, but not impossible.
2) Both FCH20U10 are bad. Two diodes bad at the same time? Maybe not.
3) F9222L might not be working 100% and causing the primary side to misbehave?

In his pdf schematic, it shows the expected voltages for F9222L. Compare it with your lcd. Pin 23 is the interesting one.

You are missing an important point. Pin 23 is the DC input for the drivers, it should be at 385V with little ripple. Pin 19 is the output of the drivers (this is called a totem pole output - Q1 and Q2 of the F9222L alternately pull it low (Q1) and high (Q2)). NOTE CM802!!!! That provides the return path for the primary windings. If it is bad you will get no output or very low output from the transformer.

PlainBill

[Toasty]

Re: Samsung Syncmaster 245BW

But, none of it works (correctly) unless you have the ~385v, correct?

Kinda like wondering why the car won't start, and nobody's checked the gas gauge...

[kmoonen]

Re: Samsung Syncmaster 245BW

CM802 is broken from the board... didnt even notice it.. I cant read the top, does anyone know what the replacement info is .?.

[Toasty]

Re: Samsung Syncmaster 245BW

More questions, still no answers...?

[PlainBill]

Re: Samsung Syncmaster 245BW

CM802 is broken from the board... didnt even notice it.. I cant read the top, does anyone know what the replacement info is .?.

It's in the schematic posted above. 18 nF, 650 volts, 5% Digi-Key stock number P14550-ND should work.

PlainBill