Samsung Syncmaster 220T - flickers.

[carbonfiber]

Hello all,
got this monitor to fix.
The symptom- when turned on, works for a minute or so but then starts to flicker slowly. sometimes the backlight just turns off momentarily and back on, but sometimes it's off for longer - and in that case the monitor just turns off and back on after couple of seconds (the whole monitor restarts) and i hear some sqeal for SMPS tranformer area.
I got 5v steady. But as for the 15v line which i suspect - with main board disconnected it measures ~17.5-18v. when monitor is working fine - this line is 14.5v (good) but while the monitor restarts this climbs up to 18-19v.
i read some posts suspecting startup cap, does it fit to symptoms ?
would appreciate any thoughts

[Rtech]

Re: Samsung Syncmaster 220T - flickers.

Normally only the 5v is regulated,so the 14.5/15v line varies with load.Using the Power supply only connected to the mains ie No Logic Board etc,measure the voltages again and see if the 5v varies.Also the DC Voltage across the BIG Cap,PLEASE BE CAREFUL.

[carbonfiber]

Re: Samsung Syncmaster 220T - flickers.

Hello Rtech and thanks for replying!
well.. BIG cap: when just plugged in without main, it fluctuates a bit between 310-313 vdc.
when monitor works 305 v, when flicker occurs - ~ 310 v.
5v is rock steady at 5.2v under all circumstances. while it shuts down momentarily i hear a clear sequel from SMPS transformer (i think) also it gets a little warm, don't know if thats OK.

[selldoor]

Re: Samsung Syncmaster 220T - flickers.

This board has been "worked" before some caps replaced and whilst C104 looks to have been moved it looks like an original? perhaps has been tested or just resoldered?
I am thinking your problem could be ccfl lamp related bulb or wiring - do you have any spare bulbs or a panel you could use to test?

[carbonfiber]

Re: Samsung Syncmaster 220T - flickers.

Hello,
this board has been worked on caps by me but with no luck.
selldoor, just tried to hook up another panel - the same symptoms appear and even worse (backlight just stays off + high pitched noise). so i suppose it's not bad lamps. i am thinking that some component is not supplying enough power, just don't know which.
any ideas?

[selldoor]

Re: Samsung Syncmaster 220T - flickers.

Ok - the caps you replaced what make are they - where did you get them?
( Thinking Ebay fakes?)
Can we have a picture of the panel board ( tcon) - may be attached to the panel?

[carbonfiber]

Re: Samsung Syncmaster 220T - flickers.

here are TCON pics,
about the caps - most Rubycon (yes, from eBay -fake? ) and some unbranded.
even if the caps are not top quality - can it cause failure even when they are new?
just did a test - connected the panel to a known working PSU - worked good. so the culprit lies in some bad PSU component. how can i test the inverter transformer? and what does the high pitched noise from MSPS transformer indicate?
many thanks for helping

[selldoor]

Re: Samsung Syncmaster 220T - flickers.

Lots of fakes on ebay and on a PSU may be bad enough to stop it working even if new.
They might work ok as general caps in a different environment.
If you have any left over post a picture in the "identifying bad caps and related syptoms" forum and see what the cap experts think- post pics of the sides, top and bottom plug.

Good testing the panel - thats another problem out of the way.

The screeching is usually caused by the transformer producing power that is not used.
so it is pumping out 15volts for the panel light and when it shuts off there is nowhere
for it to go. I will work out testing the inverter transformers and post shortly

[carbonfiber]

Re: Samsung Syncmaster 220T - flickers.

The screeching is usually caused by the transformer producing power that is not used.
so it is pumping out 15volts for the panel light and when it shuts off there is nowhere
for it to go. I will work out testing the inverter transformers and post shortly

Thanks!

[selldoor]

Re: Samsung Syncmaster 220T - flickers.

Ok Inverter transformer test.
Power OFF board doesnt need to be connected. Meter on Ohms 2000

Test S1>S2 and S3>S4 as marked on attached.

[carbonfiber]

Re: Samsung Syncmaster 220T - flickers.

hey,
i got an autoranging DMM.
i got the board disconnected. (not sure what you mean by "Power OFF board doesnt need to be connected")
resistance between S1-S2 = 1.164 kohm
resistance between S3-S4 = 1.182 kohm

[selldoor]

Re: Samsung Syncmaster 220T - flickers.

Power OFF = Monitor switched off - I usually say that since someone tried to do the test with it all connected up and switched on..

Those results are great - another thing less.

The flat cable with "Hung" on it can you see where the other end goes
does it plug directly into the panel or is there another board

[carbonfiber]

Re: Samsung Syncmaster 220T - flickers.

i see, just punctuation misunderstanding
i am posting a picture of the whole set.
if you mean the LVDS cable then it's attached directly without additional boards.

[selldoor]

Re: Samsung Syncmaster 220T - flickers.

ok well next thing to test might be the stu407DH transistors on the bottom of the power board.

Datasheet is here
http://html.alldatasheet.com/html-pd.../STU407DH.html

and testing method (for shorts) is here. This is an excellent guide for 2 seconds to black written by retiredcaps start at post19 there is a section on mosfets and transistors.
https://www.badcaps.net/forum/showthread.php?t=10419.

[carbonfiber]

Re: Samsung Syncmaster 220T - flickers.

hey,
i did the resistance measuring on the transistors and the all have kilo/Mega ohms resistances, so i beleive they are fine. i also checked them with DMM using diode mode.
some new info: the signal that is marked on the pic (on the TCON it's printed BL-EN and on the PS the same pin is labeled ON/OFF).
i noticed that when light goes out this signal drops from 2.7v to 0v.
so apparently the PS is getting a command to turn backlight off ?!
maybe the problem is in the TCON?
i am thinking maybe to cut the wire and give it a contant voltage and see if it helps. should i ? maybe better ideas?
Thanks very much so far

[selldoor]

Re: Samsung Syncmaster 220T - flickers.

I have seen this done in another post quite recently - remember to cut it where
you have enough space to splice it back together easily


EDIT - Here
https://www.badcaps.net/forum/showth...=splice&page=6

start at post 112.

[carbonfiber]

Re: Samsung Syncmaster 220T - flickers.

I just want to be sure about the direction of this signal.
Can you tell for sure that this signal is originated by TCON and going into the PSU?
some more findings:
i have found the two diodes and the regulator (all circled) to become quite warm though the output of the regulator is ~1.8v and looks stable.

[selldoor]

Re: Samsung Syncmaster 220T - flickers.

I just want to be sure about the direction of this signal.
Can you tell for sure that this signal is originated by TCON and going into the PSU?

No I am not sure either - can you trace back from pin 8 on the psu to see where it comes from/to

[selldoor]

Re: Samsung Syncmaster 220T - flickers.

While you are into voltage regulators may as well test the others IC601 in that area and one on the left side of the board.

I have to go and make Dinner so missing for an hour or so - I am surprised no others have joined us.

[carbonfiber]

Re: Samsung Syncmaster 220T - flickers.

hey thanks for the guidance!
i think i will give it a rest as well..
meanwhile i tried connecting a very similar TCON from another samsung. all the pins are match by the label. plugged it in and it was even worse - a very quick flash on start up and darkness afterwards
though with this TCON the BL_ON signal stayed 2.7v all the time and still no back light.