Samsung LN40A450C1DXZA

[Caleb]

Hello I got this tv today, It has already been worked over by someone. They replaced 4 caps in the primary (nec replacements read .02 esr) all the other larger caps read .01, there are three small caps (about 1uf) two read .33 and one is .46 Im not sure if this means they are bad or not, still trying to get used to the blue esr meter. I get standby power (5v) chime when I push power on, however no light below the logo like my other samsung.

I have 12v going from power supply to inverter board on top harness. All the transformers on the inverter read the same EXCEPT the vertical one in the center of the board it is reading as shorted across the side with 3 leads, I haven't had time to unsolder that one yet and see if it is the transformer or something else.

They seem to have damaged the flip latch for the lvds cable leaving the main board any one got an easy fix for that? I will post more testing tomorrow after I find the test leads for the oscilloscope.

[Caleb]

Re: Samsung LN40A450C1DXZA

So after spending a little time with this tv yesterday im about 90 % sure the power supply is ok, it seems to be a backlight issue. I have 12v vcc on the top harness but am not getting anything out of the hv transformers from the power supply. Both transformers in the power supply ring ok so I dont think they are faulting. I have a 5v inverter on signal coming from main board to power supply. This is the first set Ive worked on with these small inverter transformers, can anyone tell me if they are just a lower ratio, None of them ring and Im still trying to ascertain what the vertical one does. Any ideas appreciated.
Caleb

[aaronwt6]

Re: Samsung LN40A450C1DXZA

If I'm not mistaken the long strip along the side is some type of balancer board and the actual inverter is part of the power supply. Try unplugging the control board from the power supply and powering up the unit. See if the backlight comes on. Seems to me that it could still be a supply issue. Also, you shouldn't be trying to test those lower two wires for the backlight with your meter. Had they been live I believe you could have cooked the meter.

If someone else with more experience on these would like to correct anything I've said, please chime in by all means.

[johnboy1313]

Re: Samsung LN40A450C1DXZA

Does the backlight flash at power up and then cut off?

[budm]

Re: Samsung LN40A450C1DXZA

That big long board is the Balancer board, so did the backlights flash at least once as John asked? There are test points on the small multi wires on the inverter board, it should have something like FB, etc next to it.
It also has similar setup as this one:
http://www.youtube.com/watch?v=oE6K4...ature=youtu.be

Also "you shouldn't be trying to test those lower two wires for the backlight with your meter" That is correct, do not try to measure the high voltage, it can be as high as 2000V which can easily damage the meter.
Unplug the cable between the power supply/inverter board and the main board should cause the backlights to come on.

[Caleb]

Re: Samsung LN40A450C1DXZA

Ok done some more testing after I got home tonight, I DO get a 2 second flash with the top cable undone from the balancer board. Does that mean the balancer is bad? I looked them up and they are only 12$, I do have another lg board with the same small transformers I could trade out a few components, Im adding in some better pictures of the power board front and back. As well as some voltage testing I did before I read budms reply. Not to worry I didnt test the hv directly I used the oscilloscope probe on top the transformer to see if it was on. I thought I was on the trail of the culprit when I found the diode (1n5408) with no voltage on one end But it tests ok out of circuit. not really sure what thats about?

[budm]

Re: Samsung LN40A450C1DXZA

We still need to find out if the power supply PFC Voltage circuits are working or not, that is why I ask to check the DC voltage on that large filter. Those little transformers on the Balancer board are current sensing transformers that sense how much current is being drawn by each lamps as shown on that YOUTUBE video.

[Caleb]

Re: Samsung LN40A450C1DXZA

I just finished testing all the feed back points, as described in that video. from top to bottom
5.92
6.19
6.95
6.34
6.48
6.16
5.90
6.30
3.60
3.30
5.60
6.80
5.98
4.79
5.29
5.58
the only one I didnt find a test point for was that pesky vertical transformer.
what filter do you want me to test? the main caps on the power board are 393vdc

[budm]

Re: Samsung LN40A450C1DXZA

393vdc: That is good, the PFC Voltage booster is working. I am not sure about those voltage reading on those test point yet, per video, they should not be that high.
Can you take close up at one of those test point you use, also the small connector on the balancer board so I can see what kind of signal names on those pins of the connector.
I will look at shopjimmy to see if he has good pictures of the boards also.
Here is the diagram BN44-00199A with the help from Tom.
Check the voltage on the power supply board connector CNI806 FB, LD, vcc pins as shown in the diagram, at TV off and at TV ON, the voltages may appear real fast.

[Caleb]

Re: Samsung LN40A450C1DXZA

Ok here is the closeup
it reads
LD tv off no voltage either side tv on 3.86 v on power supply side tested again and saw a high of 6v
GND
FB tv off no voltage either side tv on 18.8 v inverter side
VCC is 12v with tv on 0v off with cord plugged or unplugged

do i need to do it with the cable plugged in as well? only have 12v with the cable plugged in.

[budm]

Re: Samsung LN40A450C1DXZA

I updated my post 9.

[Caleb]

Re: Samsung LN40A450C1DXZA

Im linking in the full size shot of that inverter board if you need to take a look or if you want better pics just let me know and I will post when I get home.

http://farm8.staticflickr.com/7296/9...42023f78_o.jpg

[Caleb]

Re: Samsung LN40A450C1DXZA

Any more ideas to try on this? If not I will order that replacement balancer tomorrow and give that a try. At the least I will have another to compare measurements from.

[budm]

Re: Samsung LN40A450C1DXZA

I have seen bad conncetion in those black sockets which are connections between the Balancer board and the lamps, you may want to slide the Balancer board out and inspect the sockets and the fingers of the board first, do not loosen up the screws for the black socket mounting or you may break the lamps.

[Caleb]

Re: Samsung LN40A450C1DXZA

Alright I pulled that board and all the connections appear to be ok, Im going to go ahead and order a replacement and hope the power supply is good.

[Caleb]

Re: Samsung LN40A450C1DXZA

Well I have different readings but the board swap didn't fix it. new readings top to bottom
3.98
4.27
4.34
3.89
4.34
3.90
3.88
3.82
5.6
5.18
4.3
5.18
4.89
4.47
4.38
6.02

9.69 vac on fb pin on inverter
ld leaving power board 1vdc

My question is now is it plausible for more than one to have troubles? or should I just focus on the one over 6 volts? I measured it several times averages out to about 6 volts

[tibimakai]

Re: Samsung LN40A450C1DXZA

I would take apart the screen and look at the tubes when they turn on and see if all of them turn on or not.

[budm]

Re: Samsung LN40A450C1DXZA

The FB pin should be dc volt <1V, so you can have possibility that you have lamps problem.

[Caleb]

Re: Samsung LN40A450C1DXZA

Well I was hoping not to have to dismantle it further but I will open it up the rest of the way and see what we have inside. I think I have another 40" jensen out in the parts pile, hopefully the tubes will be adaptable.

[budm]

Re: Samsung LN40A450C1DXZA

FB DC reading on working Inverter board.
LD should stays HIGH:
https://www.badcaps.net/forum/showth...=LD#post353822 POST23.
And this one:
https://www.badcaps.net/forum/showth...=LD#post349300