Samsung BN44-00264A Power Board

[cicabu72]

Re: Samsung BN44-00264A Power Board

Important update

I replaced STRW6252 with another spare part I discovered at home and TV now is powering up and shows channels, but.. it only lasts 10-15 seconds, then shuts off, standby led blink some times and TV restarts, in a sort of loop!
I feel we're very close to the solution, time to replace also CM808?

[R_J]

Re: Samsung BN44-00264A Power Board

I would replace CM804 and CM808, and even CM809 & CB804 while you are at it. Those small caps dry out over time but will look amd sometimes check ok.

[Davi.p]

Re: Samsung BN44-00264A Power Board

Keep consideration that there is a story of defective STRW sold on market, you must take them from reputable markets, like Farnell, Distrelec, RS, or at least UK sellers on ebay. You must also test psu at bench with dummy loads.

[cicabu72]

Re: Samsung BN44-00264A Power Board

I would replace CM804 and CM808, and even CM809 & CB804 while you are at it. Those small caps dry out over time but will look amd sometimes check ok.

Replaced CM804, CM808 and CB804, now TV stays ON for a longer period but after 5 minutes the loop reappears. I did not find CM809, also looking at schematics, were you referring to another capacitor?

[dick_barton]

Re: Samsung BN44-00264A Power Board

Turn down the backlights as low as you can go and still have a reasonable picture and see if it stays on longer.

[Davi.p]

Re: Samsung BN44-00264A Power Board

and this what means?

check the connectors of cable between psu and main, it may have burnt pins like the b620 that i have fixed (same psu)

[dick_barton]

Re: Samsung BN44-00264A Power Board

My error. It's a CCFL set not led so ignore turning down backlights.

[R_J]

Re: Samsung BN44-00264A Power Board

Replaced CM804, CM808 and CB804, now TV stays ON for a longer period but after 5 minutes the loop reappears. I did not find CM809, also looking at schematics, were you referring to another capacitor?

I must have made a mistake on CM809, I likely ment CP809, The small caps on the VCC lines for the primary ic's.
Check the voltage across CM804 and then check the voltage on QB801 emitter using hot ground. (or check the voltage across CP809) This voltage should be about 16vdc, These voltages will tell you if you have a high enough vcc for the ic's to stay working.

[cicabu72]

Re: Samsung BN44-00264A Power Board

I must have made a mistake on CM809, I likely ment CP809, The small caps on the VCC lines for the primary ic's.
Check the voltage across CM804 and then check the voltage on QB801 emitter using hot ground. (or check the voltage across CP809) This voltage should be about 16vdc, These voltages will tell you if you have a high enough vcc for the ic's to stay working.

Hello there, some updates after summer holidays

- Installed a brand new STRW6252 (the other was a spare part, I was not really sure if it was working properly) = same random reboots
- CM804 (replaced) reaches 18.1V when TV is ON, when a reboot appears, it drops to 16.8 and then come back to 18. I noticed that after a reboot (red power led flashing), additional reboots may also appear until TV stays ON for a while
- CB804 (replaced) stays all the time to 0.03V, is it normal?
- CP809 (replaced) but I have to test the voltage yet, the position is a little bit tricky, so I need some test clips
- I get weak signal on the channels I am watching just before a reboot, remote become unresponsive, could be this a sign that some voltages are dropping (normal conditions 12.50 on 13V and 5.1 on 5.3V, all measured on CNM802, way too low?).

[Davi.p]

Re: Samsung BN44-00264A Power Board

Read BETTER comments, i told you to: " You must also test psu at bench with dummy loads", this test is mandatory, tell me why you have to search for a board error if you don't even know if you have an error... i told you also to check cable connectors, read back..

[cicabu72]

Re: Samsung BN44-00264A Power Board

Read BETTER comments, i told you to: " You must also test psu at bench with dummy loads", this test is mandatory, tell me why you have to search for a board error if you don't even know if you have an error... i told you also to check cable connectors, read back..

I checked the pins from both side and they seem fine, multimeter in continuity mode beeped at every pin.
Anyway, today I disconnected the cable from the main board and the backlight was fine for one hour. How can I test the PSU with loads, do I need some specific equipment? Bear in mind that this is not my work, TV is mine
Nevertheless, I am now suspecting that the main board is not working properly, I told you about the weak signals just before a reboot, the unresponsiveness of the remote, but today connecting an external HDD to USB port caused many unsuccessful starts until I disconnected it (power led red flashing). Weird

[Davi.p]

Re: Samsung BN44-00264A Power Board

You need only power resistors, for the standby 5v you can load 1A, 5v/1A=5ohm/5W, 5V*1A=5W.
For the A5V you can load 2A so 2,5ohm 10w, for the 12v at least 2A, since there are not all the resistor you want take example 2 10W, so 20W/12V=1,8xxA , 12/1,8xxA=~7ohm/2=~3,3ohm/10w x2 in series.
For 12v you can use a 12v 20w ceiling or car lamp, halogen

[cicabu72]

Re: Samsung BN44-00264A Power Board

You need only power resistors, for the standby 5v you can load 1A, 5v/1A=5ohm/5W, 5V*1A=5W.
For the A5V you can load 2A so 2,5ohm 10w, for the 12v at least 2A, since there are not all the resistor you want take example 2 10W, so 20W/12V=1,8xxA , 12/1,8xxA=~7ohm/2=~3,3ohm/10w x2 in series.
For 12v you can use a 12v 20w ceiling or car lamp, halogen

I connected a 12V 40W halogen lamp to 12V connector CNM802, I can say that the lamp stayed ON for 1 hour with the same intensity. Power board seems stable in this condition, but I noticed that I am not getting 12V but 10.3V (on the connector) and 9.5V on the pins towards the lamp. The only connected load is the lamp right now, as you can see in the image. What do you think, should I proceed with 5V tests?

[Davi.p]

Re: Samsung BN44-00264A Power Board

The board must be load on all outputs, 1h is too much time, needed only 1min. and see the voltage across load, anyway since the 12v and B5V comes from the same transformer i guess there's a problem in the feedback components, change the tl431 small TO92 component and the optocoupler connected to it.

[cicabu72]

Re: Samsung BN44-00264A Power Board

The board must be load on all outputs, 1h is too much time, needed only 1min. and see the voltage across load, anyway since the 12v and B5V comes from the same transformer i guess there's a problem in the feedback components, change the tl431 small TO92 component and the optocoupler connected to it.

Do you mean QB801? What is the optocoupler name in the circuit?

[Davi.p]

Re: Samsung BN44-00264A Power Board

I can't judge by a photo, and my board is too much "infognated" :-)))), check under side across the thick black line there are 3 - 4 pins components one attached to the other, them are optocouplers, watching that zone there are some sot23 components, one is marked 431 on the body and Uxxx on the position, that is the tl431 i mentioned and is pin connected to the right opto. Good luck..

[cicabu72]

Re: Samsung BN44-00264A Power Board

I can't judge by a photo, and my board is too much "infognated" :-)))), check under side across the thick black line there are 3 - 4 pins components one attached to the other, them are optocouplers, watching that zone there are some sot23 components, one is marked 431 on the body and Uxxx on the position, that is the tl431 i mentioned and is pin connected to the right opto. Good luck..

QB801 (on the front) has D1347 C K913 on it and seems to be a TO92 component. Can you tell me if you see the optocouples in the attached image (back)? Thank you!

[Davi.p]

Re: Samsung BN44-00264A Power Board

Leave alone TO92 package, i was expecting that but 431 is in format sot23, search it to the right of those three opto in your last photo.

[cicabu72]

Re: Samsung BN44-00264A Power Board

Leave alone TO92 package, i was expecting that but 431 is in format sot23, search it to the right of those three opto in your last photo.

I think I found it, UM801, in the scheme is marked as KA431SLMF2, but I was not able to read tl431 on top of it. In the attached image you can see it, is it possible to do some test with a multimeter before replacing it?

[Davi.p]

Re: Samsung BN44-00264A Power Board

My last mess. seems lost... as i've said it is printed only 431, it has a pin connected to the right opto
checking it is.maybe possible but to be safer better to replace it.
..