need help to test inverter transformer

[selldoor]

Re: need help to test inverter transformer

good - were you able to find a panel with that type of backlight connector?
If not ,I am not sure how the Big plugs are wired -perhaps budm will suggest how you
can best test the bulbs

[woaimi]

Re: need help to test inverter transformer

that is my problem right now, I couldn't find anything with that plug, my bulbs mostly came from computer LCD and the biggest size i have is 19". There are 6 plugs for this tv set and I'm assuming it represent 6 bulbs, here's what I'm thinking will I cause any damage if I only plug in 1 or 2 bulbs to the corresponding transformer and leave the other unplug? this way I can verify which transformer is working and which one is not and may be at the same time can figure out the questionable bulb/s.

[selldoor]

Re: need help to test inverter transformer

I am hoping all transformers will be good and we can work out which lamp or lamps is
causing the shut down. As I said budm has more ideas on this and has a way of using
old domestic energy saving bulbs to test so we need to hope he comes back to this thread. For testing the size of your panels doesnt matter I think you can get adapter from small to big but for now just see if you can plug a small plug in onto one pin of the big connector. If it will go on then we can consider cutting the small plug in half.

[woaimi]

Re: need help to test inverter transformer

I measured the Vcc input to the transformers and reading 56v at all time whether the TV is on nor not, does that suggest anything?

[budm]

Re: need help to test inverter transformer

OK, I looked at the inverter/power supply board, all three transformers are driven by the same output MOSFET's. I still think you should have replace all 3 transformers.
You have indicated that you have 56V at all time on the inverter transformers primary side. It should have 0 Volt due to DC blocking cap, and the junction between the two inverter MOSFET's should have 0V (not 100% sure since I did not draw out the circuits in details). I would take that blue DC blocking cap out and measure for any leakage resistance using the highest Ohm scale, cap should show open circuits, you should also check its capacitance.
Another thing you can check to see if all the lamps do at least try to light up or not by just having one set of lamp connector connected one at a time, then turn on the TV in the dark room and see if each set of the lamp will light/flash.
I will tell you later how to use home made tester lamp.

[woaimi]

Re: need help to test inverter transformer

Wow, thanks for that drawing, I've learned much more since I take on this project. Thanks for all those replies.
I checked the light bulbs one at a time and they're all flashed up in the same pattern; it flashes like twice in about 5 seconds, I think they are fine.
The DC blocking cap were removed to test, it read opened when test with the ohm meter and the capacitance measured 0.452 nF and the caps's label said 474K (I'm guessing that 's a 0.47 nF cap)

[budm]

Re: need help to test inverter transformer

It is 0.47uF cap not 0.47nF.

[woaimi]

Re: need help to test inverter transformer

thanks budm for pointing it out, i will have it verify later tonight, I might have mis-read the 'u' and 'n' on the meter.

[woaimi]

Re: need help to test inverter transformer

It was verified as 452nF, that's what happened when I tried to work on it at 2:00 am. So, going back to your drawing, if I can't measure those 2 points you mentioned how can I verify it 0 voltage? I'm feeling very close to get it working, really don't want to throw in the towel yet.

[selldoor]

Re: need help to test inverter transformer

Perhaps just replace it - I dont think they are v expensive? perhaps you have one on a "spares" board?

[woaimi]

Re: need help to test inverter transformer

Could you please help to id this cap? all I can tell is .47uF, don't know what the voltage rating. I probably be able to find it in my junk pile. Thanks

sorry for the blurry image, that's the best i can come up with with my iphone.

[selldoor]

Re: need help to test inverter transformer

I dont know but thought id say something to bring it back to the top.
Is the K relative to 1000 or is it a tolerance value - I have seen some with a J.
The 4 could be 400v is there a voltage on the small blue cap next to it?

[woaimi]

Re: need help to test inverter transformer

there's nothing written on the small cap either. From what I found the 3rd character is the multiplier and K is tolerance value of +-10%

[selldoor]

Re: need help to test inverter transformer

Yes that was what I thought - in the absence of more educated input I would try a 400v - I have looked at a few and some are just coded so 4 could be anything. Can you get a better close up of the logo in the middle of the bottom line - if anyone recognises that we might find the codes.

[woaimi]

Re: need help to test inverter transformer

I'll try with a real camera later when I get home.
Anyhow, I wanted to retake the voltage reading off the connector so I soldered it back on last night, plugged everything in, turned it on. I realized I was able to see the screen with a spot light. I checked the transformers in frequency mode to find out they were all run at 63 kHz (if I remember correctly) and all shut down as the screen goes dark.
The CN600 connector reads as follow
V-PWM = 0.54V/ 0.54V (on/off)
BL-ON = 5.15V/ 65mV
PS-ON = 4.7V/ 4.7V
GND
GND
5V = 5.2V / 5.2V
5V = 5.2V / 5.2V
5V = 5.2V / 5.2V
5VS = 5.2V / 5.2V
GND
GND
12.5V = 12.7V / 12.9V
12.5V = 12.7V / 12.9V

I also took reading at the secondary diodes (D601, D605, D607) but forgot what they were
I hope that would give the experienced users some more details to work with.

[budm]

Re: need help to test inverter transformer

That cap should be 630V or higher due to high voltage pulse.

http://www.digikey.com/product-detai...F6474-ND/56678

Bythe way:
474k = 470000 pico farad(pF is x 10 to the minus 12) = .47uF (uF is x10 to the minus 6), K = 10% tolerance)

[selldoor]

Re: need help to test inverter transformer

Right - that is the blue cap sorted then. I think we need to have a look at the Tcon board it is under a metal panel in one of your pics. Can you get to it and take some pictures - I think there will be fuses on it to test.
Have you tried unplugging the lead to the Tcon from the main board to see if that allows the backlights to stay on?

[woaimi]

Re: need help to test inverter transformer

whew! my 2 little boys are really know how to keep daddy busy, finally able to break away from them to work on this tv set

that is the blue cap sorted

I couldn't find 1 similar from my pile of electronic junk so I guess I will have to order the replacement.

I think there will be fuses on it to test

I scanned through the t-con board and couldn't find any fuse, may be someone can help me spot it. I hope the photo is clear enough

Have you tried unplugging the lead to the Tcon from the main board to see if that allows the backlights to stay on?

I have not tried this because I currently have couple mosfet off the pcb for testing.
As I mentioned, I de-soldered these 2 mostfet U603 & U600 of the board to test (using retiredcaps instruction). The part numbers are P65NF06 & FQP17P06. The test (setting @ 200 ohm)result are "1" on every pair of leads. Isn't that suggested the mosfet are bad?

EDIT: i found the fuse on t-com board, so obvious can't believe I missed it. It labeled on board as F1 and has letter K on the fuse itself. It measured 0.4 ohm, i think that meas it's good.

[selldoor]

Re: need help to test inverter transformer

As I mentioned, I de-soldered these 2 mostfet U603 & U600 of the board to test (using retiredcaps instruction). The part numbers are P65NF06 & FQP17P06. The test (setting @ 200 ohm)result are "1" on every pair of leads. Isn't that suggested the mosfet are bad?

Yes - just check that the "1" is one ohms and not "1" meaning "out of range"
would would mean they are likely ok.

EDIT: i found the fuse on t-com board, so obvious can't believe I missed it. It labeled on board as F1 and has letter K on the fuse itself. It measured 0.4
ohm, i think that means it's good.

Yes fuse is good- There are at least 2 voltage regulators on that board
They will need checking if new mosfets and blue cap doesnt fix it.

[woaimi]

Re: need help to test inverter transformer

that was the "1" on the left, so it's out of range
I'm waiting for the blue cap in order, I'll update with result later. Thanks