Ex Serviceman Needs Help

[adrianed]

After 15 years retired and never having serviced a flat screen Tv I am hoping someone might help me to repair my own TV
Its a Samsung La40C 550 Jif
The power board is well known Code BN44-00340B
The Tv has sound and the picture can be seen with a flashlight but the backlights are off
The voltage on the two big yellow caps is 322volts across its two leads, same for each of them which I think is probably a bit low
The voltage doesn't change if I unplug the Tv main board
No appearance of hot spots anywhere on the board
I would buy another power board if I could be sure that the problem is not on the next board that supplies power to the lights
Any suggestions would be welcome
Adrian

[Gdog215]

Re: Ex Serviceman Needs Help

Try unplugging the main board from the power board, than power on the tv. See if the backlights come on first than you will know if your power board is good and main board Is bad. You should get a lighted blue screen. Try that first.

[R_J]

Re: Ex Serviceman Needs Help

Is the fuse FI801s ok? what voltage do you get on the fuse (use hot ground)? Have a close look at CI802 cap. and either check it or look to see if is bulged. also check for poor connections on any fets etc. mounted to heat sinks.

[maxvalutech]

Re: Ex Serviceman Needs Help

The LA40 series from memory 2008/9 ?? The main connector will have pson and blon marked ?? As you have a picture you need to see if blon is being generated by mainboard. To do this you disconnect main and jumper the pson pin to earth and the blon pin to a 5v pin. If backlights come on then mainboard problem if not PSU circuit problem. All from memory so others may correct me. Use low value resistors if you have them for jumpers.

[maxvalutech]

Re: Ex Serviceman Needs Help

I see R_J has supplied a circuit and the connector has a PWM pin so may need to jumper that to 5v as well as the others.

[dick_barton]

Re: Ex Serviceman Needs Help

Your PFC voltage does seem low considering the capacitors CP801, CP803 are rated at 450V. I would have though it to be more towards 400V

[budm]

Re: Ex Serviceman Needs Help

It looks like PFC circuit is not running, the 323V on the cap is normal for 230VAC input Australia.

[dick_barton]

Re: Ex Serviceman Needs Help

What voltage do you have between pins 6 & 8 of ICP801

[adrianed]

Re: Ex Serviceman Needs Help

Hi Folks,
Thankyou all for the suggestions about repairing my TV
I looked very closely at the circuit board and found what looked like dry joints
I heated them up with the soldering iron to remelt the joints and after that the TV came on working again like magic
All the good suggestions prompted me to take time and look it over and it paid off
Thankyou all again
Adrianed

[dick_barton]

Re: Ex Serviceman Needs Help

What voltage do you now have on a working set between pins 6 & 8 of ICP801 and also what PFC voltage do you have at FI801S. This information would be useful for others to know should they have a similar fault.

[adrianed]

Re: Ex Serviceman Needs Help

Dick there is no ICP801 on this board
There is only one IC and the number is ICM801
There are only six pins and the pin no's are not shown

Adrianed

[budm]

Re: Ex Serviceman Needs Help

There are many SMD parts on the bottom side of the board, look there.

[adrianed]

Re: Ex Serviceman Needs Help

I did overlook that, yes there are quite few components underneath the board, I avoided them when I was retouching the solder joints, I had thought that if any of these very small components require changing I could not do it with the iron I have and I would almost require a microscope
It will take me some time to take the board out again being as I have put it all together for using and let my daughter have it
I will get the voltage for you though in due course
Adrianed

[budm]

Re: Ex Serviceman Needs Help

BTW, you will be making the Voltage in the HOT DEALY side of the circuit so you should at least plug the TV into GFCI outlet.
The GND for your meter will be the negative leg of the main DC filter cap, you will have to power up the board and have the board flipped over, so do not touch anything with your hands or body, use insulation sheet to lay the board on so nothing on the board will touch the chassis.

[adrianed]

Re: Ex Serviceman Needs Help

Thanks budm
Adrianed