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Old 11-18-2010, 08:33 AM   #1
newbie1
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Default Samsung 2233sw '2sec to black'. Need guidance please.

Hi guys,

& another one comes along..

Symptom/Problem
-2sec to black. Image visible if using torch light.
-If i leave the monitor on longer, 20 sec later the backlight will lit up again for about 2sec... then off.
-Power LED steady blue

Description/what's been done.. or not
- Age around 2-3years, But it is an export set so no warranty.
- No schematics at hand
- Have not replaced all caps because they all 'look' to be super fine. But will replace them if advised to do so.
- Use another panel (my 'dead' HP f1905 and working hp w20) to test ccfl (subtitute them one at a time or all at once), but still 2sec to black result.

Unplugged & measured resistances
- no short in between pins of D101(in circuit) & D107 (out of circuit)
- U201 BD9893F Pin 16 (Vcc) not shorted to Pin 6 (Gnd)
- on T301 (in-circuit)
: P1 =open to all
: P2 =1.2ohms to P3, increasing to P4, open to the rest,
: P3 =1.2ohms to P2, increasing to P4, open to the rest,
: P4 =increasing until max to P2, P3
: S1 to S2 =897ohms,
: S3 to S4 =initially 1500-1520ohms but drops to 943ohms after re-testing it again & again
: S1&S2 to S3&S4 = 191k ohms

Plugged & measured Voltages = backlight on (off)
- across Big cap = 330V (330V)
- CN2
13V = 12.2V (14.19) both unstable
5V = 5.2V (5.21V) both stable
3V = 3.27 (3.27) both stable
- U201 BD9893F
Pin 16 (VCC) = 11.01 (10.9)
Pin 9 (Comp) = 0.61 (0.51)
- on T301
: S1 & S2 - Over volt (almost busted my DMM again)
: S3 & S4 - 6.2-6.5V?!!

So 1 side of the transformer is reading less voltage than the other.. So is this transformer faulty & need to be replaced?.
Or are there other components or test points that i missed out?..
Am i troubleshooting it correctly?..
Hope the experts here can guide me along.. again thanks..
Attached Images
File Type: jpg 2233sw top.jpg (404.2 KB, 567 views)
File Type: jpg 2233sw btm-1.jpg (458.8 KB, 392 views)
Attached Files
File Type: pdf bd9893f-e.pdf (155.9 KB, 386 views)

Last edited by newbie1; 11-18-2010 at 08:36 AM..
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Old 11-18-2010, 09:19 AM   #2
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Default Re: Samsung 2233sw '2sec to black'. Need guidance please.

Hello! I'm guessing that U202 is a duo mosfet (?) that is used to drive the inverter transformer. Try checking it for shorts.


Don't try measuring the inverter voltage output (approx 700-900VAC).


: S1 to S2 =897ohms,
: S3 to S4 =initially 1500-1520ohms but drops to 943ohms after re-testing it again & again
: S1&S2 to S3&S4 = 191k ohms

Odd transformer readings. You may have to remove it from the board and retest S1&S2, S3&S4.

Last edited by jetadm123; 11-18-2010 at 09:40 AM..
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Old 11-18-2010, 10:30 AM   #3
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Default Re: Samsung 2233sw '2sec to black'. Need guidance please.

Quote:
Originally Posted by newbie1 View Post
Hi guys,

- Use another panel (my 'dead' HP f1905 and working hp w20) to test ccfl
so you're sayign you HAVE done this? just clarifying.



also, what brand(s) are those caps. those yellow guys (or gals) look an awful lot like the "yc" and identical "fuhjyyus" (so same copmany i guess) that were completely bad. thanks...
and yes if they are a crap brand i may have you replace the m
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Old 11-18-2010, 11:01 AM   #4
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Default Re: Samsung 2233sw '2sec to black'. Need guidance please.

Quote:
Originally Posted by newbie1 View Post
Symptom/Problem
-If i leave the monitor on longer, 20 sec later the backlight will lit up again for about 2sec... then off.
Odd, this is the first time I have seen anyone report this particularity.

Quote:
- on T301 (in-circuit)
: S1 to S2 =897ohms,
: S3 to S4 =initially 1500-1520ohms but drops to 943ohms after re-testing it again & again
Odd that it jumps and then settles.

Quote:
Plugged & measured Voltages = backlight on (off)
- CN2
13V = 12.2V (14.19) both unstable
5V = 5.2V (5.21V) both stable
3V = 3.27 (3.27) both stable
- on T301
: S1 & S2 - Over volt (almost busted my DMM again)
: S3 & S4 - 6.2-6.5V?!!
Like jetadm123 said, don't try measuring the voltage. 700V AC can do more than just damage your multimeter. You could be on the floor hoping someone calls 911.

On the 13V rail, please clarify what you mean by unstable? Does the voltage drop steadily or flucutate all over the place? What caps are on the 13V rail? They should be the caps that are rated 25V and higher.

PS. Great clear focused pics.
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Old 11-18-2010, 11:06 AM   #5
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Default Re: Samsung 2233sw '2sec to black'. Need guidance please.

@retiredcaps: why did you say that the 13v caps should be 25v rated at minimum? 16v caps would be fine, right?
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Old 11-18-2010, 11:37 AM   #6
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Default Re: Samsung 2233sw '2sec to black'. Need guidance please.

Quote:
Originally Posted by shovenose View Post
@retiredcaps: why did you say that the 13v caps should be 25v rated at minimum? 16v caps would be fine, right?
Almost all the LCDs that I have worked on have caps voltage ratings significantly higher than the "desired" voltage. Significantly means 50% higher or higher. These past observations made me think of 25V instead of 16V.

16V would be fine, but it doesn't leave much "headroom" if the voltage were to momentarily go higher than the "desired" 13V.

I don't think there is a correct answer here. I think it depends on the original design criteria and how conservative the designers are in choosing their tolerances.
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Old 11-18-2010, 12:21 PM   #7
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Default Re: Samsung 2233sw '2sec to black'. Need guidance please.

Quote:
Originally Posted by shovenose View Post
@retiredcaps: why did you say that the 13v caps should be 25v rated at minimum? 16v caps would be fine, right?
No. On most power supplies the 5V supply is regulated, the other (12V, 13V, etc) is not. In this case, 13V is the nominal voltage under load - with the CCFLs on. It will go higher if the CCFLs are off. The power supply is on whenever the monitor is plugged in. That means that there is very little margin. Spend the extra $.10 and get caps with an adequate voltage margin.

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Old 11-18-2010, 06:49 PM   #8
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Default Re: Samsung 2233sw '2sec to black'. Need guidance please.

hey guys, thanks for all your inputs. I will try to clarify/answer all the queries here. If I am not clear enough in my explanation or missout something, do ask more..

* CCFL - yes, shovenose. I did swap the CCFL with another panel. Same result.

* U202 (Dual channel Mode FET - STU312D) - jetadm123, using DMM set at 200, I cannot detect any shorting in between the pins. thanks for the info about the output voltage of the transformer.

* retiredcaps, noted on the warning. I certainly do not want any incident or accident to happen here. Yes, i feel its odd as well that if i leave it on a little while longer the backlight light-up then 2sec to black again. As for the transformer S3 to S4 resistance, initial reading when i opened it up was 1500-1520ohms, AFTER i did all the voltage measurements i measured it again & it drops to 943ohms. Now, after overnight, it is still steady at 940+ohms.
For the 13V, what i mean by unstable is that at backlight on, it reads 12.2V but when off it fluctuates between 14.19-14.90V. Not forgetting the caps, I have labelled the top side pix (thanks for the compliment, takes me a hell lot of hours waiting for the right sunshine angle to take them), kindly see below
Cap A - don't know what brand, dark blue color, what i can see is W0C PET, rating hidden below, 4x11 (estimated mm as i am using ruler, not calliper)
Cap B - Samyoung, NXB 330uf 10V, 7x10
Cap C - Samyoung, NXH 1000uf 10V, 10x12
Cap D - Samyoung, NXB 820uf 25V, 10x20
Cap E - don't know what brand, dark blue color, what i can see is WF W9C PET, 47uf 50V, 6x10
add: oops i just noticed while typing that i missed C116, i think its the same size with C114 (Cap A) but light blue in color.

* PlainBill, thanks for sharing the information on the caps.. $0.10 certainly wouldn't justify cracking open the LCD again.. better be safe, rather than.... having my fingernails bruised again..

Next, I should be de-soldering the transfomer & measure resistance again right?. What kind of resistance you guys suspect I should be getting?..
Attached Images
File Type: jpg 2233sw top-1.jpg (403.3 KB, 223 views)
Attached Files
File Type: pdf stu312D datasheet.pdf (177.9 KB, 189 views)

Last edited by newbie1; 11-18-2010 at 06:55 PM..
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Old 11-18-2010, 07:07 PM   #9
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Default Re: Samsung 2233sw '2sec to black'. Need guidance please.

You say,
“If i leave the monitor on longer, 20 sec later the backlight will lit up again for about 2sec... then off.”
Will the monitor continue to do this over and over if you leave it plugged in?
Al.
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Old 11-18-2010, 07:15 PM   #10
retiredcaps
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Default Re: Samsung 2233sw '2sec to black'. Need guidance please.

Quote:
Originally Posted by newbie1 View Post
For the 13V, what i mean by unstable is that at backlight on, it reads 12.2V but when off it fluctuates between 14.19-14.90V.

Cap D - Samyoung, NXB 820uf 25V, 10x20
I'm off somewhere, but will leave a quick note and check back later.

With LCD plugged in and power OFF, measure the diode (just next to R105) for DC V. The middle pin should be where the red probe goes and a ground screw for the black probe. It should read a steady 14.xy DC V.

If it is steady, I suggest replacing the 820uF 25V caps to see if that solves the problem. As a test, you can use anything handy if you don't have the proper low ESR caps. Even 1000uF 25V as a temp test should work? You cn replace them 1 at a time or all 3. I would do 1 at a time, but that is me trying to find "root" cause.

My suspicion is that 12.2V is too low.

If that works, replace all the caps afterwards.
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Old 11-18-2010, 07:49 PM   #11
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Default Re: Samsung 2233sw '2sec to black'. Need guidance please.

Quote:
Originally Posted by newbie1 View Post
hey guys, thanks for all your inputs. I will try to clarify/answer all the queries here. If I am not clear enough in my explanation or missout something, do ask more..

<SNIP>

Next, I should be de-soldering the transfomer & measure resistance again right?. What kind of resistance you guys suspect I should be getting?..
Definitely desolder the transformer and measure the secondaries. I would expect something in the 890-920 ohm range and both windings match to within 3%.

Several people have mentioned that the backlights coming back on after the 'two seconds to black' is unusual. One possibile explanation is the BD9893F contains an over-temperature shut down circuit.

PlainBill
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Old 11-18-2010, 10:43 PM   #12
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Default Re: Samsung 2233sw '2sec to black'. Need guidance please.

Quote:
Originally Posted by retiredcaps View Post
..., I suggest replacing the 820uF 25V caps to see if that solves the problem. ...
I agreed , I should do according to retiredcaps's recommendation first.

Caps may be fail even they're look good, and I guess they're already failed.
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Old 11-19-2010, 01:02 AM   #13
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Default Re: Samsung 2233sw '2sec to black'. Need guidance please.

I have noticed in other Monitors where there are Diodes in the Main Tmfr secondary,and not just Schottky diodes,to produce the 5v and 12v etc etc, that without a load the voltage does look unstable, but is fine on load.I would not concern myself with that at the moment.
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Old 11-19-2010, 04:07 AM   #14
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Default Re: Samsung 2233sw '2sec to black'. Need guidance please.

this is what i can afford to update as of now,

*Al, nope. I did try to leave it for about 1 min but it did the 2sec-to-black twice only.. One during start-up & the second one 20sec later.. After that couldn't detect anymore 2sec-to-black..

* retiredcaps & POM_MJ ('sawadee krap', fellow Asian), I manage to swap the three caps 820uf 25v (one at a time) with three caps 1000uf 25V Panasonic FM (12.5x20mm) & here are the result of the voltage measurement taken at middle pin of the diode (D107)
[backlight on > backlight off-power led on > all off but power plugged]
= 1st cap changed - 12.2V > 14.18V > 13.43V
= 2nd & 3rd cap changed - same as above
FYI, i did further measure some other points near the secondaries (see attached), hope i did the right thing
[backlight on > backlight off-power led on]
V1 = 3.7V > 0V
V2, V3, V4,V5 = 0V > 0V
V6 = 0V! > 0V
I am a bit puzzled by this, why V6 is not reading the same as V1?.. hhmm.. Is it indicating transformer problem or circuit on that side of the transformer?..

*Rtech, thanks for sharing.. i think swapping caps still gives me 12.2V at backlight on, which i kinda belief caps are not causing this problem.. anyway, if you guys think otherwise, i am open to all ideas..

*PlainBill, sorry i could not desolder & measure the transformer yet,, The 'Queen' is having her shopping session & i'm stuck with my little rascals at home.. ..I will try to do it in a few hours time..
Attached Images
File Type: jpg 2233sw btm-2.jpg (459.0 KB, 227 views)
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Old 11-19-2010, 05:15 AM   #15
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Default Re: Samsung 2233sw '2sec to black'. Need guidance please.

Quote:
Originally Posted by newbie1 View Post
* retiredcaps & POM_MJ ('sawadee krap', fellow Asian), I manage to swap the three caps 820uf 25v (one at a time) with three caps 1000uf 25V Panasonic FM (12.5x20mm) & here are the result of the voltage measurement taken at middle pin of the diode (D107)
[backlight on > backlight off-power led on > all off but power plugged]
= 1st cap changed - 12.2V > 14.18V > 13.43V
= 2nd & 3rd cap changed - same as above ...
Yes, 'Sawasdee Krab' is greeting in Thai language.

While [backlight on] and you've got 12.2V, the temp. of D107 is just warm or too hot?
if it too hot, maybe voltage drop by overload in your CCFLs drive circuit.
if not, the 13.8V supply has defected somewhere.
just guess.
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Old 11-19-2010, 05:17 AM   #16
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Default Re: Samsung 2233sw '2sec to black'. Need guidance please.

Quote:
Originally Posted by newbie1 View Post
FYI, i did further measure some other points near the secondaries (see attached), hope i did the right thing
[backlight on > backlight off-power led on]
V1 = 3.7V > 0V
V2, V3, V4,V5 = 0V > 0V
V6 = 0V! > 0V
I am a bit puzzled by this, why V6 is not reading the same as V1?.. hhmm.. Is it indicating transformer problem or circuit on that side of the transformer?..
Just to add, I did swap the pair of CCFL connectors but voltage readings on V1 to V7 are the same.
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Old 11-19-2010, 05:27 AM   #17
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Default Re: Samsung 2233sw '2sec to black'. Need guidance please.

Quote:
Originally Posted by POM_MJ View Post
Yes, 'Sawasdee Krab' is greeting in Thai language.

While [backlight on] and you've got 12.2V, the temp. of D107 is just warm or too hot?
if it too hot, maybe voltage drop by overload in your CCFLs drive circuit.
if not, the 13.8V supply has defected somewhere.
just guess.
thanks.. I did not notice earlier & now I have already de-soldered the transformer.. Maybe later once I have re-assembled, i take note of it..
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Old 11-19-2010, 05:44 AM   #18
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Default Re: Samsung 2233sw '2sec to black'. Need guidance please.

Quote:
Originally Posted by PlainBill View Post
Definitely desolder the transformer and measure the secondaries. I would expect something in the 890-920 ohm range and both windings match to within 3%.

Several people have mentioned that the backlights coming back on after the 'two seconds to black' is unusual. One possibile explanation is the BD9893F contains an over-temperature shut down circuit.

PlainBill
Ok managed to re-soldered the transformer & measure the resistance

- on T301 (out-of-circuit)
: P1 = open to all
: P2 = 0.3ohms to P3, open to the rest,
: P3 = 0.3ohms to P3, open to the rest,
: P4 = open to all
: S1 to S2 = 904ohms,
: S3 to S4 = 981ohms

comparing to T301 (in-circuit)
: P1 =open to all
: P2 =1.2ohms to P3, increasing to P4, open to the rest,
: P3 =1.2ohms to P2, increasing to P4, open to the rest,
: P4 =increasing to P2, P3
: S1 to S2 =897ohms,
: S3 to S4 =initially 1500-1520ohms but drops to 943ohms after re-testing it again & again
: S1&S2 to S3&S4 = 191k ohms

Any thoughts?

So currently, on the board now are the replaced 13V caps (820uf) with 1000uf and it is without Transformer T301..
Attached Images
File Type: jpg T301-top.jpg (272.6 KB, 208 views)
File Type: jpg T301-btm.jpg (286.9 KB, 205 views)

Last edited by newbie1; 11-19-2010 at 05:47 AM..
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Old 11-19-2010, 08:35 AM   #19
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Default Re: Samsung 2233sw '2sec to black'. Need guidance please.

Looks to be a greater than 3% difference between S1&S2, S3&S4. Suggest you start looking for a new inverter transformer.
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Old 11-19-2010, 10:54 AM   #20
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Default Re: Samsung 2233sw '2sec to black'. Need guidance please.

Quote:
Originally Posted by jetadm123 View Post
Looks to be a greater than 3% difference between S1&S2, S3&S4. Suggest you start looking for a new inverter transformer.
$16 USD on ebay.

http://cgi.ebay.ca/TM-0815-Inverter-...-/150488882117

Seller is in Hong Kong.
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