samsung LE40B551A6W black screen with sound

[andrewblueboy]

hi all

i have a samsung LE40B551A6W black screen with sound, when i got it i new a bulb needed changing, (my mistake took bulb holder off and broke tube) then tested all bulbs and all worked fine. now ive put it all together.
so now this is how i got the tv no picture but with sound. iive taken the in power inverter board off and checkedthe transformers and come a cross a difference in the readings.
heres a pic to explain

the one on the right has different readings, could this be the cause or is it normal as this one has a different letter with black edgeing tape

any infor appricated

thankyou

[R_J]

Re: samsung LE40B551A6W black screen with sound

That transformer on the right is different as it only has to drive 2 lamps, the others each drive 4 lamps. both secodaries on that check the same so it is likely ok.
Do you at least get a quick flash of the backlights when first turned on?
If you disconnect the plug going to the main board do the backlights come on?
On the first 3 transformers primaries you show OL, that is not right, it should be low around 1 Ω or less

Also on the first 3 transformers the two secondaries are not connected together, on the third one they do connect the secondaries together at the 2 center pins. this is normal
Another item to check is CI817 (square white cap) If it looks slightly bulged it is bad

[Andrew F. Ali]

Re: samsung LE40B551A6W black screen with sound

I am not sure but I think the transformers should carry the same numbers and the odd numbered one seems to be bad one. Wait on others to chime in before deciding.

[R_J]

Re: samsung LE40B551A6W black screen with sound

You may want to check the connections on the circuit side of the board, all the transformer primaries should be connected in parallel, so if TI804 measures 1395, that is wrong, it should be very low, like a short.

[andrewblueboy]

Re: samsung LE40B551A6W black screen with sound

That transformer on the right is different as it only has to drive 2 lamps, the others each drive 4 lamps. both secodaries on that check the same so it is likely ok.
Do you at least get a quick flash of the backlights when first turned on?
If you disconnect the plug going to the main board do the backlights come on?
On the first 3 transformers primaries you show OL, that is not right, it should be low around 1 Ω or less

Also on the first 3 transformers the two secondaries are not connected together, on the third one they do connect the secondaries together at the 2 center pins. this is normal
Another item to check is CI817 (square white cap) If it looks slightly bulged it is bad

the meter i use is a fluke 113 so i used the ohms as auto, i shall try the manual range and see if it measures 1 or less.
i shall try in the morning and see how i get on

thanks for your input

[andrewblueboy]

Re: samsung LE40B551A6W black screen with sound

ive the measurement in the different range and the only one that seems diff is the one on the right on pic its 0.2 as it jumps from 0.2 to 0.1 and

CI187 0.435 v one way and OL differenr direction.

in ohms its 3265 one way OL different location and not swollen

[andrewblueboy]

Re: samsung LE40B551A6W black screen with sound

hi all

ive taken readings with tv on and standby hopefully it will help out as to how the tv is at the momment. when on tv blank but you can see the snow effect on tv channel with a torch. so for some reason the back light is going off after 2 seconds

[R_J]

Re: samsung LE40B551A6W black screen with sound

If the backlights come on for 2 seconds, I suspect the inverter board is ok, and there is a bad ccfl lamp in the panel.
The backlight will shut off if it sees an error on one of the ccfl's ie: it did'nt light. It could be hard to isolate as you can't just disconnect a single lamp output and it can be hard to see if all the lamps light for 2 sec without opening the panel.

as for CI187, it must be ok if you get the 2 sec.of backlight, also it can't be checked with a multimeter unless it has a capacitor test function.

[R_J]

Re: samsung LE40B551A6W black screen with sound

I was just over at another repair shop and noticed the same board sitting around, he said he had 3 tv's and all had bad ccfl's and the boards were all good, so it is a good bet a ccfl is bad in your tv.

[andrewblueboy]

Re: samsung LE40B551A6W black screen with sound

thankyou for comments about the ccfl, looks light this will be the next job taking it apart again and test those bulbs.

[andrewblueboy]

Re: samsung LE40B551A6W black screen with sound

right this time i used my light tester and all re working but yet the tv stays on, no green light or anything just has if the tv was off . with torch still snow haze and with sound. im now stuck on this now never seem to get any further.

[R_J]

Re: samsung LE40B551A6W black screen with sound

How are you testing the ccfl tubes? check the lamp contacts, they sometimes go bad

[andrewblueboy]

Re: samsung LE40B551A6W black screen with sound

just switched the main board with another and still the same problem

[andrewblueboy]

Re: samsung LE40B551A6W black screen with sound

How are you testing the ccfl tubes? check the lamp contacts, they sometimes go bad

hi

i have a ccfl tube tester i took inverter boar off and place neg on back panel and postive in the slot that the invertor board slides into and i can see the tube light up thro the holes in back panel

when i first got tv had i had tv stripped down and tested them on both ends and they were fine.

now they come on 2 secounds give a little buzz then off

[dick_barton]

Re: samsung LE40B551A6W black screen with sound

Where did you get the replacement tube from. Perhaps it's not to the same specification as the ones you already have in the set and may be causing an error signal.


On the prmary side of each CCFL transformers, have you checked (using you meter set to ohms) that pin1 of each of the transformers are connect together and also all the pin 2's are all connect together. As suggested by RJ in post #4

When you power up what voltage do you have at DET_5V?. If it's low then there is an error.

What voltage do you have at the Inverter On/OFF pin when you power up?

[andrewblueboy]

Re: samsung LE40B551A6W black screen with sound

Where did you get the replacement tube from. Perhaps it's not to the same specification as the ones you already have in the set and may be causing an error signal.

the tube was from ebay same model of tv. i shall be dismantling the tv again tomorrow checking bulbs and connectors incase anything loose causing a short.

if i take front off down to the tubes can i attach power invertor board and power up. would this be safe to see what happens or is this a NO leaving the tubes exposed

thankyou for your input and also to others who have given me advice on this tv

[dick_barton]

Re: samsung LE40B551A6W black screen with sound

You can do all the checks mentioned before stripping down the set.

Also worth viewing the following youtube video

[andrewblueboy]

Re: samsung LE40B551A6W black screen with sound

Where did you get the replacement tube from. Perhaps it's not to the same specification as the ones you already have in the set and may be causing an error signal.


On the prmary side of each CCFL transformers, have you checked (using you meter set to ohms) that pin1 of each of the transformers are connect together and also all the pin 2's are all connect together. As suggested by RJ in post #4

When you power up what voltage do you have at DET_5V?. If it's low then there is an error.

What voltage do you have at the Inverter On/OFF pin when you power up?

the inverter on /off as far as i can rember no reading as that why i left it blank on my picture i added
the 5v det when on showed OL, think im going after recheck these readings

you mentioned the primary pin 1 and 2 primary , im not sure how you mean with this .
still a huge learning curve this for me and very greatfull with the infor. im determind to get this working even tho its a challange

[dick_barton]

Re: samsung LE40B551A6W black screen with sound

It's the dc voltages at the pin 23 & 25 being asked for. With the black lead on the chassis and red meter lead on Pin 23 (Inverter On/Off), power on the set and give the voltage the meter reads. Repeat for pin 25 (Det_5V)

With the set off and using your meter set to ohms do all the "A" connect together and all the "B"

[budm]

Re: samsung LE40B551A6W black screen with sound

Most CCFL tester does not have detection/.protection circuit to detect lamp over current draw, bad worn out lamp (which draw more current than normal) will still light up with tester so keep that in mind.
Det_5V is normally HIGH (it is active low, LOW = PROBLEM in backlights circuit).