need help to test inverter transformer

[woaimi]

Re: need help to test inverter transformer

I tested the 2 mosfets (photo attached) again using 200 ohm method and the readings between pin 1&3 on both mosfet read only 22 ohm, but they were fine when being test off circuit. I soldered them back and measure voltage around that area. All measurement was done using the filter cap (-) pin as ground point. I did used the chassis ground but the reading were very much different, in the mV range. There are not much around the mosfets, I tested them all and they seem to do fine, unless they break when applied loads.
What do you think of those voltage readings? what causing both mosfet to display 22 ohm between 1-3 on circuit test?

[selldoor]

Re: need help to test inverter transformer

Was just hoping I caught you before you wrestled it off the board.
159 is a bit low should be 1.41 x your mains. when the set is plugged in but off. If it has PFC it should be higher when the power button is pressed.

[woaimi]

Re: need help to test inverter transformer

i left out that fact, I had all 3 meters in DC to begin with. silly! thanks selldoor

[selldoor]

Re: need help to test inverter transformer

Just check its not an odd-ball rectifier what marking on pins?

When you take it off see what voltage you have at the holes for the ~~ pins. should be mains 115AC
You did have meter on AC?

[woaimi]

Re: need help to test inverter transformer

yeah, that's what I thought too, so I used 3 meters to confirm that reading. I'm de-soldering that rectifier to test off circuit.

[selldoor]

Re: need help to test inverter transformer

If I have read what you say correctly , better start testing again, again It should be impossible to get a voltage at the Big Cap if its not at the Bridge Rectifier.

[woaimi]

Re: need help to test inverter transformer

OK, so out of frustration and disappointment,i decided to restart the whole testing process from beginning. With power on, measure cross the filtering caps read 159v, probing the middle pins of the bridge rectifier I get 52mV. I think I should get 115V right folks?

[selldoor]

Re: need help to test inverter transformer

Are you still getting the 56V permanently on the input to the transformers- just to check is that ac or dc.
Were you able to find/test the voltage regulators on the tcon.

[woaimi]

Re: need help to test inverter transformer

well, I got the cap from digikey to replace the blue cap today, it didn't make anything different. I disconnect the t-con board from the main board, the screen would still goes away after a few seconds. Am I running out of option?

[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

[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

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

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?

[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)

[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.

[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

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

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

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

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