[Syncmaster 245B Plus] Problems with power board BN44-00195A

[FredFloete]

Hello everbody!

Two weeks ago my old good Samsung Syncmaster 245B Plus with a faint hiss. So I took a look into the problem and found many problems with the BN44-00195A (https://cdn.badcaps-static.com/pdfs/...f8a620fd8c.pdf) on the internet. Also here, where some users had problems with bad caps. In my case all caps are looking fine and the problem may be a bit more complicated.

After I took a look at the power board if found a blown resistor with the number RM801 (22 Ohm, 1W). The two fuses were also blown. I replaced the resistor and the two fuses and gave it another shot. What could I say. Seconds after putting the power back on the same resistor has been blown again.

So I tried to find more faulty components on the power board. It seems that the diodes DM804 and DM809 are also faulty. I tried to test them with my multimeter and current flows in both directions. As far as I can tell QM802 and QM803 are still fine.

So at the moment I’ve no clue what caused this damage and I’m sure when I replace the diodes too everything will blow up again.

Does anybody of you had any kind of experience with this error and could provide me some hints where I have to look next? Thanks a lot!

[euromatlox]

Re: [Syncmaster 245B Plus] Problems with power board BN44-00195A

Best option is to use board BN44-00173A instead. Of course before buying/trying that it's recommended to check that other parts (boards) are ok. Those board also cost some money, and you must also decide what is your limit to spend.

For BN44-00173A it is recommended to replace at least 4 electrolytic caps and three 68ohm resistors. To be more safe, some other resistors and caps can be replaced too. You can easily find information about this procedure.

It's common that that '195A' has some broken smd components too. If you like to battle with that board, search some older information in this forum, for instance:

https://www.badcaps.net/forum/showthread.php?t=22008

[FredFloete]

Re: [Syncmaster 245B Plus] Problems with power board BN44-00195A

For BN44-00173A it is recommended to replace at least 4 electrolytic caps and three 68ohm resistors. To be more safe, some other resistors and caps can be replaced too. You can easily find information about this procedure.

It's common that that '195A' has some broken smd components too.

Thanks for the reply. Are the 00173A and 195A fully compatible? By replacing these components do you think this is just about the aging process of the components or do I have to do it before replacing the board in general?

And what did you mean by saying the 195A has some broken smd components? In case of a failure or in general? Can you imaging what causes the error of the burning resister on my power board?

[euromatlox]

Re: [Syncmaster 245B Plus] Problems with power board BN44-00195A

Are the 00173A and 195A fully compatible?
And what did you mean by saying the 195A has some broken smd components? In case of a failure or in general? Can you imaging what causes the error of the burning resister on my power board?

Yes, those boards are fully compatible, at least when '195A' is replaced with '173A'. If I remember correct, there is a small amperage difference, the amperage table is printed in the board.

I have installed '173A' inside a 245B plus, which model originally had '195A'. Very easy replacement, but of course must be careful, for instance that black plastic insulating piece under the board must not be forgotten.

SMD components are those very very tiny (and usually black color) components in the other side of the power board. In my '195A' it was a smd zener diode, which was broken. I replaced it and some caps - board worked for a while, but soon stopped working. I ended up using '173A' instead.

I have heard that the glue they use around the board can become conductive, that might be one explanation. Those carbon resistors are originally only 1W (power) resistors. In '173A' it's common that some of those three serially connected 68ohm 1W resistors will burn in (long) time. Recommended is to replace them with 68ohm 2W (or 3W) resistors. I have personally replaced also the other two 'upward' resistors (which usually have some glue in them) with bigger wattage ones.

If resistor burns immediately or very soon, and possibly with some smoke in the air, then it indicates some kind of short circuit somewhere.

[Joe Black]

Re: [Syncmaster 245B Plus] Problems with power board BN44-00195A

After I took a look at the power board if found a blown resistor with the number RM801 (22 Ohm, 1W). The two fuses were also blown. I replaced the resistor and the two fuses and gave it another shot. What could I say. Seconds after putting the power back on the same resistor has been blown again.

So I tried to find more faulty components on the power board. It seems that the diodes DM804 and DM809 are also faulty. I tried to test them with my multimeter and current flows in both directions. As far as I can tell QM802 and QM803 are still fine.

So at the moment I've no clue what caused this damage and I'm sure when I replace the diodes too everything will blow up again.

Have you checked for a short? Start by posting nice clear pictures of your board...

[budm]

Re: [Syncmaster 245B Plus] Problems with power board BN44-00195A

Did you remove ALL the glues?
Snubber cap CM810 not shorted?

[FredFloete]

Re: [Syncmaster 245B Plus] Problems with power board BN44-00195A

Hi guys,

thank you for your replies. I added some pictures of the pcb. Tbh I dont know how I can remove the glue without damaging some of the components. Its very hard to remove all the glue with a screwdriver or something similar. The burned resistor is missing in the pcb because i soldered it out already.

[euromatlox]

Re: [Syncmaster 245B Plus] Problems with power board BN44-00195A

You can check the 8008HFE regulator if it's shorted or otherwise broken. I did replace that part in my '195A' expirement, since the readings I got using a multimeter felt abnormal. There are also three electrolytic capacitors quite near it, I recommend replacing them all, although they seem to be okay in the picture.

https://www.semicon.sanken-ele.co.jp...il/SI-8008HFE/

You might also want to check some SMD parts too:

https://www.badcaps.net/forum/showth...t=18966&page=2

[budm]

Re: [Syncmaster 245B Plus] Problems with power board BN44-00195A

https://www.badcaps.net/forum/attach...4&d=1476304736
Check the resistance between the two legs of that small blue cap covered all over with glue, it is just above jumper J824, that is one of the high Voltage section.
You also have lots of glue on the resistors by the ICB801S.
See what bad glues will do to your board.
https://www.badcaps.net/forum/showth...ight=bad+glues

[FredFloete]

Re: [Syncmaster 245B Plus] Problems with power board BN44-00195A

You can check the 8008HFE regulator if it's shorted or otherwise broken. I did replace that part in my '195A' expirement, since the readings I got using a multimeter felt abnormal. There are also three electrolytic capacitors quite near it, I recommend replacing them all, although they seem to be okay in the picture.

https://www.semicon.sanken-ele.co.jp...il/SI-8008HFE/

You might also want to check some SMD parts too:

https://www.badcaps.net/forum/showth...t=18966&page=2

Maybe I'm blind but I was not able to locate the SI-8008HFE. do I have to desolder the parts before testing? Beside that I think checking the SMDs are a pain in the ... . And because I'm not that experienced in electronics, I'm not able to replace SMD parts atm. Its said, I know...

https://www.badcaps.net/forum/attach...4&d=1476304736
Check the resistance between the two legs of that small blue cap covered all over with glue, it is just above jumper J824, that is one of the high Voltage section.
You also have lots of glue on the resistors by the ICB801S.
See what bad glues will do to your board.
https://www.badcaps.net/forum/showth...ight=bad+glues

The varistor above J824 its CM809 and shows ~1.99 kOhm. There is a 2nd part which looks like varistor called CM802 which only has a resistance 0.5 Ohm. The schematic says 47pF/1KV, so it might be just a capacitor.

The two resistors you mentioned are RB802 and RB801. one has 72 the other 75 kOhm. Seems fine to me. Anyway do you have a tip how to get rid of the glue without damaging any components? What do you use?

[euromatlox]

Re: [Syncmaster 245B Plus] Problems with power board BN44-00195A

The SI-8008HFE is behind a coil, the one on right side. It has five legs. All other similar looking components on board have only three legs.

The most suspicious glue is there near the biggest electrolytic capacitor, it seems to have some color changes. I'm not a big believer of the 'glue theory', at least multimeter measurements (resistance) have shown nothing extraordinary. I think the glue must have had some enviromental changes (raise of temperature, burning) to become conductive. But I'm not a 'professor' in these things. If only a millimeter or half is the distance between component legs, and glue is located there 'connecting them', it might be better to remove the glue somehow using a knife etc.

I still have a spare '195A' (which is probably broken however). There seems to be different type of glue in the legs of FQPF9N50C mosfet transistors, which are in the middle of the board near the 'huge capacitor'. That seems pretty suspicious to me...I think there might be some glue in your '195A' too. I would remove that glue.

I have replaced some electrolytic caps and resistors of four 245B:s, each having '173A' board. Those have since then worked without problems. Never done any SMD repair for that version of power board.

[budm]

Re: [Syncmaster 245B Plus] Problems with power board BN44-00195A

"The varistor above J824 its CM809 and shows ~1.99 kOhm. There is a 2nd part which looks like varistor called CM802 which only has a resistance 0.5 Ohm. "
CM = CAPACITOR. You need to remove those caps to measure the resistance off the board, good cap should show open circuit.

[FredFloete]

Re: [Syncmaster 245B Plus] Problems with power board BN44-00195A

"The varistor above J824 its CM809 and shows ~1.99 kOhm. There is a 2nd part which looks like varistor called CM802 which only has a resistance 0.5 Ohm. "
CM = CAPACITOR. You need to remove those caps to measure the resistance off the board, good cap should show open circuit.

THIS power supply is causing me nightmares. I dont know what happened here, but I'm a huge amound of bad luck trying to fix this thingy. After I desoldered CM809, the PCB around the whole went off and I lost contact to the items marked red in the picture I attached. So my question here is: Can I just make a bridge with a cable to one of these components? Not sure because all of the in the red marked zone are connected to each other regarding my continuity test. Anny tips here?

The SI-8008HFE is behind a coil, the one on right side. It has five legs. All other similar looking components on board have only three legs.

I removed most of the glue. Will see what will happen next.

[euromatlox]

Re: [Syncmaster 245B Plus] Problems with power board BN44-00195A

Sometimes happens that pcb copper film breaks away, and then the only solution is to fix the circuit by soldering some wire. Of course must be careful that the connections are electrically similar as before. Some glue (non conducting hot melt glue) can be helpful in this situation too.

[FredFloete]

Re: [Syncmaster 245B Plus] Problems with power board BN44-00195A

Sometimes happens that pcb copper film breaks away, and then the only solution is to fix the circuit by soldering some wire. Of course must be careful that the connections are electrically similar as before. Some glue (non conducting hot melt glue) can be helpful in this situation too.

Can I solder the broken part (see picture) to any of the other solder joints?

[R_J]

Re: [Syncmaster 245B Plus] Problems with power board BN44-00195A

Just solder a piece of wire between the two points to reconnect the broken trace

[FredFloete]

Re: [Syncmaster 245B Plus] Problems with power board BN44-00195A

"The varistor above J824 its CM809 and shows ~1.99 kOhm. There is a 2nd part which looks like varistor called CM802 which only has a resistance 0.5 Ohm. "
CM = CAPACITOR. You need to remove those caps to measure the resistance off the board, good cap should show open circuit.

So I desoldered the both Caps and my multimeter showed 0L in resistance mode. I also removed the glue as good as I could for components who are connected/bridged by the glue. But still the same error. After replacing the fault transistor the new one burned instantly. So the glue wasnt the fault in my case. Till I only have a mm here I dont know how to check 8008HFE. Any suggestions?

[budm]

Re: [Syncmaster 245B Plus] Problems with power board BN44-00195A

So the cap CM802 did not show 0.5 Ohms reading off the board that means the short circuit has to be top MOSFET QM802 is shorted or the cap CM803 which is connected in PARALLEL with QM802 is shorted, but for sure QM803 is shorted for sure for you to get 0.5 Ohms on the CM802'S solder pads because QM802 is connected in SERIES with QM803.
"After replacing the fault transistor the new one burned instantly." So which fault transistor is that?
See the pictures to see how those parts are connected to form the circuit.

[FredFloete]

Re: [Syncmaster 245B Plus] Problems with power board BN44-00195A

So the cap CM802 did not show 0.5 Ohms reading off the board that means the short circuit has to be top MOSFET QM802 is shorted or the cap CM803 which is connected in PARALLEL with QM802 is shorted, but for sure QM803 is shorted for sure for you to get 0.5 Ohms on the CM802'S solder pads because QM802 is connected in SERIES with QM803.
"After replacing the fault transistor the new one burned instantly." So which fault transistor is that?
See the pictures to see how those parts are connected to form the circuit.

I desoldered CM802 and my mm showed 0L. I havent measured the solder pads. Instead I measured the CM802 while still at the board. Therefore I got results of 0.7 Ohm dropping to 0.1 Ohm slowly after 5 seconds. I also attached a picture which resistor burned. Its my fault, it wasnt a transistor that blows, still the same resistor I replaced for the 2nd time now for testing purposes.

[budm]

Re: [Syncmaster 245B Plus] Problems with power board BN44-00195A

As explained and as you can see the marking I made on the board, you still have shorted circuit on the board since the the Cm802 shows OL. You need to check those Two MOSFETs by checking the resistance between S and D pin for low resistance.
Btw, leave out the resistor for now when checking the MOSFETs.