samsung 226bw

[liquias]

Hi,
This is my first post here.
First I'd like to thank the creators of this forum, and everyone involved in helping out. I think you are doing a wonderful job !

I am trying to troubleshoot a samsung syncmaster 226bw.
The monitor apears to be completely dead. no blue led, not 2 seconds to black, nothing.
I opened it up and looked for bloated caps on the power supply board. found 4 bloated caps. I decided to recap all electrolytic caps on the power supply board. nothing ! (no blue led , and I can't turn on the monitor).
I found a service manual for the 226bw (which is only close to the circuits in the monitor) and started checking for voltages.

Listed are the voltages I found at the connector to the logic board:
Pin 1-> ~0v should be ~0v
Pins 2,3,4 -> 0v (these are gnd pins)
Pins 5,6,7 -> 15.2v should be 13V
Pin 8 -> ~0v
Pin 9 -> 0.465v I think this should be higher.

Now, on the logic board I found the three regulators for 5V 3.3V and for 1.8V to be working fine (all output the correct output).
I scoped the crystal oscillator and it oscillates at the correct frequency.

Pictures of the boards are after recapping the PS board. I can also upload the service manual for the monitor if needed.

At this point I ran out of ideas.

Any ideas ?

[jetadm123]

Re: samsung 226bw

The 15.2V is probably ok, since it's an unregulated output and will drop under load. Do you have an idea what pin 9 is for? Have you checked the output voltage for the buck regulator, IC702?

[liquias]

Re: samsung 226bw

Hi,
On the PCB pin 9 is described as 'on/off' which makes sense as I fear this must be related with the problem.
The service manual describes pin 9 to be 'BL_EN' I'm guessing 'BackLight_Enable' ?

IC702 - 1501-50 Buck regulator for 5v gives 5.12v

Thanks !

[jetadm123]

Re: samsung 226bw

Pin 9 should read approx 3.0-3.3v. Also, try reseating the cable at both ends that connects the pushbutton switch to the logic board. It appears that transistor Q601 is connected to pin 9. Try checking it for shorts.

It also might help if you posted the schematic of the logic board.

[liquias]

Re: samsung 226bw

Q601 is definitely not shorted.
I can trace the 0.465v back to pin 1 of the LM353 OpAmp IC (see schematic).
I suspect it might have something to do with the problem also.

Cable is seated OK, also it's not shorted or disconnected, I've double checked that.

I'm posting the schematic I found, but it's only close to the logic circuit (The general idea looks the same but parts are a little different and part numbering is way off).

Again, thank you!

[jetadm123]

Re: samsung 226bw

From your schematic, any chance that what's called C709 (connected to pin 1 of the LM353) is shorted to ground?

At this point, I've pretty much run out of ideas.

[liquias]

Re: samsung 226bw

Well, I have to admit I haven't checked it specifically, but i'm sure its not, since if C709 was shorted I would find a short between the transistor's (Q601/Q700->SM) collector and emitter, and as I mentioned above the transistor is surely not shorted. Plus, I don't know which cap on the PCB is the one marked as C709 in the schematic (C611 or maybe C610 ??).

I am wondering though, in your opinion, is it safe to assume the problem is within the logic board ?
I would like to find the problem, and so I haven't given up yet, but if all else will fail, I might consider getting a whole new logic board.
I would love to know if you, or anyone else, might think of something more that comes to mind...

jetadm123, do you have any chance to measure voltages across this circuit? can you say what is the voltage across pins 4 and 8 of the LM-393 OpAmp? can you say what you see on pins 3,2,1 of this IC ?

Does anyone know what IC204 on the actual board does? What is it?

[jetadm123]

Re: samsung 226bw

Well, I have to admit I haven't checked it specifically, but i'm sure its not, since if C709 was shorted I would find a short between the transistor's (Q601/Q700->SM) collector and emitter, and as I mentioned above the transistor is surely not shorted. Plus, I don't know which cap on the PCB is the one marked as C709 in the schematic (C611 or maybe C610 ??).

I am wondering though, in your opinion, is it safe to assume the problem is within the logic board ?
I would like to find the problem, and so I haven't given up yet, but if all else will fail, I might consider getting a whole new logic board.
I would love to know if you, or anyone else, might think of something more that comes to mind...

jetadm123, do you have any chance to measure voltages across this circuit? can you say what is the voltage across pins 4 and 8 of the LM-393 OpAmp? can you say what you see on pins 3,2,1 of this IC ?

Does anyone know what IC204 on the actual board does? What is it?

Apparently, the 223BW also used the same logic board. You can take a look at this link:

https://www.badcaps.net/forum/showth...ighlight=223bw

Unfortunately, they were not able to solve the problem.

Please note that I don't have this model board in front of me, so I can't measure anything for you. I'm going strictly by your photos, my own experience and the schematic you supplied.

Yes, I do think the logic board is at fault and replacement boards are available on Ebay.

Can you read the part number off of IC204?

[liquias]

Re: samsung 226bw

Well thanks, I've actually read this post before I delved into the details of the problem I have, and so I didn't notice it was the same logic board.

I've also found this post :
https://www.badcaps.net/forum/showth...=SAMSUNG+226BW
In-which da.chisel seems to have the exact same problem I have, and retiredcaps suggests it may be a problem with the 3.3v regulator.

I double checked, the 3.3v regulator seems fine.

jetadm123, you had such accurate insight that I never realized you don't have the board (monitor) to take measures from. (: I guess this means you are doing a great job !

The part number of IC204 on my logic board is :
6P 741
In other picture posts I've found, I see that 6P is reoccurring and that the second segment (741) is a different number on every board.

so my guess is that the part number is only 6P.

SMD can be so frustrating!

[retiredcaps]

Re: samsung 226bw

In-which da.chisel seems to have the exact same problem I have, and retiredcaps suggests it may be a problem with the 3.3v regulator.

I never heard back if replacing those voltage regulators worked or not. When people don't update their thread it could be:

1) they got it fixed, but never came back to update the thread or thank people.

2) some people post on multiple boards and they may have found their answer on another board and don't bother with #1 above.

3) they gave up.

4) something happened to them and fixing it is a low priority.

5) they lost all initiative and interest?

PS. Those are excellent pictures.

[liquias]

Re: samsung 226bw

Yeah, I figured it must be something like that. It's nice to know you follow up on your threads even when they are only mentioned as reference...

But hey, maybe you have an idea what the mystery IC204 is ?
Its marked 6P and it's an SOT223-4 package.

I'm clueless.
anyone ???

[retiredcaps]

Re: samsung 226bw

Its marked 6P and it's an SOT223-4 package.

I searched for "mendel ve ic204" and found

http://www.scribd.com/doc/61780258/S...NW-216BW-sw77i

says it is an

IC-Vol detector; 7024; sot-89; 3p,-,plasti

which might be

[jetadm123]

Re: samsung 226bw

Have you tried measuring the input pin voltage of the LM353 op amp when pressing the power on/off button on the front panel? Also, measure the Vcc voltage of that op amp. If you see no voltage change, then check the continuity of the on/off switch itself.

[liquias]

Re: samsung 226bw

retiredcaps:
Thanks. I don't know how I missed this in the service manual. It does seem like this is the right description for IC204. I thought this section of the service manual (Electrical part list) is useless in my case, since schematics is not very accurate.

jetadm123:
I will take these measurements as soon as I can and I will update.
I did check for voltage change (while pressing the button) in the input of the op amp, and I think I did not see any. I will double check this when I take the voltages. I am sure though that continuity to the ON/OFF switch is fine because:
a) I checked it for shorts and open connections.
b) I later checked voltages on the connector to the buttons panel. I get 3X1.8v and one gnd. one of the 1.8v pulls down to 0v when I press the power button.
I guess somewhere on the logic board this signal is lost. As I said, I will double check.

I am about to have less time on my hands, and so I think it might take me some time to go further into repairing this screen.

I PROMISE to update as soon as I have new details.

Thank you both !
Liquias.

[franzz]

Re: samsung 226bw

Is this thread still alive? I'm having exactly the same problem with exactly the same monitor.

All the voltages are ok, except Pin 9 of the connector, which is 0.7V. I traced this back to the pin #1 of IC603 (LM393).

Now, as far as I understand, Pin 1 of LM393 should be 5V if Pin 3 (5V) is higher than Pin 2 (3.3V), right? On the other hand, the (inaccurate) schematics from the service manual show a transistor (Q700) here, which could pull it down.

Another thing I noticed is that R226 (next to IC204) is missing. It's also missing on my board, and on the one from da.chisel on the other thread.

If there is anything I can do to hel get these monitors running again, let me know (today or tomorrow - then I'll be off for a few weeks)

Thanks

[PlainBill]

Re: samsung 226bw

Is this thread still alive? I'm having exactly the same problem with exactly the same monitor.

All the voltages are ok, except Pin 9 of the connector, which is 0.7V. I traced this back to the pin #1 of IC603 (LM393).

Now, as far as I understand, Pin 1 of LM393 should be 5V if Pin 3 (5V) is higher than Pin 2 (3.3V), right? On the other hand, the (inaccurate) schematics from the service manual show a transistor (Q700) here, which could pull it down.

Another thing I noticed is that R226 (next to IC204) is missing. It's also missing on my board, and on the one from da.chisel on the other thread.

If there is anything I can do to hel get these monitors running again, let me know (today or tomorrow - then I'll be off for a few weeks)

Thanks

All threads are alive.

One of the problems with old threads is a post that starts exactly like yours. Frequently the poster has a different monitor or different problem. As it is, I have no idea what problem the OP had, and would have to read through 16 posts to find out.

There are perhaps a dozen of us regulars, and if it is too difficult to figure out the problem we often skip to the next thread. So here's the way to get attention:

It's not necessary to start a new thread, and you have done a significant amount of troubleshooting - I prefer to help those who are trying to help themselves. In your next post provide a brief description of the problem. Also a few pictures would help - one over-all picture of the cards in the monitor, and another of both top and bottom sides of the board that you are focusing on. Attach the pictures using 'Manage Attachments - below the test entry area.

PlainBill

[liquias]

Re: samsung 226bw

This thread IS alive, as fa as I'm concerned.
I have some exams in the near future so I can't do much.
Please let me know if I can help....


Liquias.

[franzz]

Re: samsung 226bw

As it is, I have no idea what problem the OP had, and would have to read through 16 posts to find out.

Thanks Bill. I'll be on a business trip now, but after that I'll be back with all information.

Franz

[Scenic]

Re: samsung 226bw

I'm still alive as well. And I still have the dead 223BW jetadm123 linked to my old thread in post #8

Curious if someone finally finds out what's wrong with the Mendel_VE (BN41-00885B) mainboard.
I'm tempted to buy a "universal" mainboard from the overly friendly chinese guys on ebay to finally fix this thing, even though that'll be quite a botch job to wire up..

[paulp246]

Re: samsung 226bw

Q601 is definitely not shorted.
I can trace the 0.465v back to pin 1 of the LM353 OpAmp IC (see schematic).
I suspect it might have something to do with the problem also.

Cable is seated OK, also it's not shorted or disconnected, I've double checked that.

I'm posting the schematic I found, but it's only close to the logic circuit (The general idea looks the same but parts are a little different and part numbering is way off).

Again, thank you!

Will you post the power supply schematic? I have a 226BW and may be able to help.