Samsung SyncMaster 204b

[whotopia]

I have 3 Samsung 204b monitors. 1st-dead after period of long startup times, 2nd-long time to start up, 3rd seems relatively fine.

I bought appropriate capacitors from Digi-Key. For PSU (on 1st unit) I had to replace 3x330uf, 2x820uF & 1x47uF. Hopefully the other 3 monitors are the same as I bought them all at once.

After replacing caps monitor #1 still doesn't work. Some debugging: 13v present to main board, C105 has around 130V on it when on (with switch). Sometimes when I turn the unit on, the blue light will be on power briefly, but typically not (still a charged cap problem)?

Could the problem be the main board? I could test this theory by swapping main board from a working monitor. Could I harm the main board? Is it better to see if I actually fixed the power supply by swapping that into a unit where the main board is working?
Any other test points I should check?

[budm]

Re: Samsung SyncMaster 204b

Any pictures of the boards? There are more than one version of this model.
http://s807.photobucket.com/user/bud...?sort=3&page=1
http://s807.photobucket.com/user/bud...?sort=3&page=1
http://s807.photobucket.com/user/bud...?sort=3&page=1

[whotopia]

Re: Samsung SyncMaster 204b

Hi,
I've attached 2 pics of the PS board and the main logic board. After a bit more debugging, still no luck. However, I did find and buy a replacement PS for only 23usd on eBay. Once it arrives that may be helpful. I still haven't disassembled my other 2 semi-working monitors because I'm using them.

[whotopia]

Re: Samsung SyncMaster 204b

So I swapped in the new power supply, and there was NO improvement.
Therefore the problem must be with the Logic/Driver. I ordered a new one from here:
http://www.baoseek.com/index.php?mai...id=24434988294
But there are plenty of other source online for purchase.

I'd still like to get this logic board working. Can anyone suggest e.g. the top 5 things that may be broken?

Thanks!

[barthez]

Re: Samsung SyncMaster 204b

Apparently I'm stuck with the same problem as whotopia. I've got two 204B monitors. The first (A) failed years ago, but is working fine since replacement of the caps. Now the second (B) showed the known symptoms. I replaced the caps but the monitor won't power up.

By exchanging power boards and logic boards between the two monitors, I've confirmed both power boards to work fine, but the logic board from B causes the following behaviour: When the mains switch is turned on, the power button LED on the front panel lights up once. Same behaviour with all other parts exchanged (power board, LCD panel, control panel).

I'm more a software guy, so I'm at a loss as to what I should test next. Any hints will be much appreciated!

The logic board:
http://s1.directupload.net/file/d/3463/4tcuqrvn_jpg.htm

[Davi.p]

Re: Samsung SyncMaster 204b

Barthez as from the picture test the voltage on the electrolytic more to the left and the big pin on the 3 legs chip "1084-33"..

[barthez]

Re: Samsung SyncMaster 204b

Davi.p, thanks for your reply! I've measured as per your post and a few other points: http://s1.directupload.net/file/d/3464/pcgvs586_jpg.htm

[selldoor]

Re: Samsung SyncMaster 204b

those vrs look ok
It is useful for future help seekers if you upload the pictures to badcaps


Failure of these boards is common and difficult to pinpoint.
could be the genesis chip or any of the dozen small switching transistors.

How many of us switch everything off before plugging stuff in??

[Davi.p]

Re: Samsung SyncMaster 204b

The readings seems to be ok.. unfortunately ..
i only have a doubt on that cap marked with a 0,17v reading,
Barthez do you confirm the same as whotopia, therefore the mon. came dead gradually?
there's no much logic but can you test without power the transistor Q301 near the previous cap? After that try to put power and measure voltage on Q301 leg's down right, if is not it it's the down left, you must read i think 5v, i think it's a P mosfet.

[barthez]

Re: Samsung SyncMaster 204b

selldoo, Davi.p, thanks! The monitor died a slow, flickering death. Since I knew the problem from its sibling, I wasn't too worried. Maybe I killed an IC with a static discharge while removing the power board?

The code on the transistor looks like "TR7 N". I found a datasheet for TR7, which seems to be matching what you wrote, Davi.p:

With the red probe on the top pin (drain?), I get 6,2 kΩ to bottom right (source?) and 51.6 kΩ to bottom left (gate?). With the black probe on the top pin, I get 17 kΩ to bottom right and 115 kΩ to bottom left. Powered on, I get 5 V on bottom right, 4.54 V on bottom left, and top 0.17 V.

[Davi.p]

Re: Samsung SyncMaster 204b

Maybe I killed an IC with a static discharge while removing the power board?

in don't know but i think not.

The code on the transistor looks like "TR7 N". I found a datasheet for TR7,

it is that..

With the red probe on the top pin (drain?), I get 6,2 kΩ to bottom right (source?) and 51.6 kΩ to bottom left (gate?)...

i'm not confident with the ohm measurements, i use diode mode, anyway it seems that is not opened/shorted, please, tell me the panel (not monitor) model.. i would like to see if in these nowadays models there is a sort of serial comm that inform the mainb. if the panel is working..
i would want to say that these tests are a very little hope..

[barthez]

Re: Samsung SyncMaster 204b

i'm not confident with the ohm measurements, i use diode mode, anyway it seems that is not opened/shorted,

Using diode mode, I get "1" from top to bottom left and from bottom left to bottom right – both ways. For top to bottom right I get 1890 with the black probe at the top pin and 368 the other way round.

please, tell me the panel (not monitor) model.. i would like to see if in these nowadays models there is a sort of serial comm that inform the mainb. if the panel is working..
i would want to say that these tests are a very little hope..

That would be "LTM201UX-L01", I guess. The panel is OK, as verified using the logic board from the other 204B.

[Davi.p]

Re: Samsung SyncMaster 204b

there is anything like what i said about the panel, therefore i say that this path is unuseful.. sorry.. the p-mosfet switches panel on and off (for energy saving for example) but if he stay off is probably due to a malfunction of the mcu or what else, but i think not an IC becouse usually them fails in one time, the only thing remains to think to from what i've read on repairing guides is the quarz crystal oscillator.

[barthez]

Re: Samsung SyncMaster 204b

Thanks, Davi.p! If I read correctly, you're saying the mosfet is OK? Then, why don't the 4.5 V on the gate (?) suffice to make more of the 5 V on source flow through the mosfet to drain? My apologies if my question doesn't make any sense, last time I tried to learn some electronics theory I was a good 20 years younger…

Later this week I'll replace my old 204Bs, then I can cross-check between the working logic board and this one.

[Davi.p]

Re: Samsung SyncMaster 204b

plus.. on a Italian forum i've read about a tv equipped with a service rs232 line, it would not turn on, by connecting a pc he saw that it powered up correctly but it would not continue to boot, by sending a sequence of Esc characters it has booted and the tv became fully usable even in next times.. this is called programmed obsolescence...

[whotopia]

Re: Samsung SyncMaster 204b

I now have an oscilloscope at home for another project. I'm also going to try to cross check the logic board against a working in the coming days (weeks? have a day job too )
The replacement board that ordered from China still hasn't arrived Hope I haven't been scammed there.

[whotopia]

Re: Samsung SyncMaster 204b

Probably final update on this issue.

I ended up buying a replacement logic board for the monitor from DHgate. The board seemed to work fine until I connected the monitor to my hackintosh. Then, it would go black for a few seconds every few minutes. Weird.

After a bit of googling around, I discovered this is a known problem with 204B and some video cards. Apparently at full resolution 1600x1200 some 204B logic boards cannot handle 60Hz input. Sure enough, I tested the monitor at other resolutions and refresh rates, and all was well. I decided I would live with this issue, though my other 2 monitors work fine at 60Hz. There is a utility out there for OS X called SwitchResX which allows fine control of the refresh rates on multi-monitor configurations. I bought this little utility, set all the monitors to refresh at 58Hz, and now all is well. I'm pleased with the results, and this will hold me until I ultimately decide to replace all 3 screens.

[jetadm123]

Re: Samsung SyncMaster 204b

Thanks for reporting back on this issue. Many people don't give feedback on whether they got their monitor working and it adds to the frustration as to whether member's suggestions are helping or not.