need help to test inverter transformer

[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?

[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

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

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

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

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

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

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 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

Will need Budm to comment on that - can you give us a rundown again on what happens when it is all connected and with a working source, from plug in via power on to stable fault position. What do any leds do what does the screen do - any sound any noises - clicks etc.
Disconnect the cable from the main board to the Tcon and try again.

[woaimi]

Re: need help to test inverter transformer

OK this is what the set behavior. As soon as power cord plugs in (without a need to press the ON button) the set comes on for about 5 seconds, shows a perfect screen then the screen goes dark. Sound is still on. The blue led that came on when plugged in power still blue. I'm able to see the screen content with a flashlight. If I press the power button to turn it off then on again I would see that same behavior repeat again.
I disconnected the t-com board from the main board, the screen come on a few second flashes away then come back a few second then gone. So, it's pretty much the same with the t-com connected, with just a blank screen.
I tested 1 bulb at a time with the others disconnected. I can see it flashed on went away and flashed back on within 5 seconds then stay off after that. All bulbs show the same pattern.

[selldoor]

Re: need help to test inverter transformer

Ok so on that basis all seems to work except the back lights which shut down
irrespective of the main board. This seems to suggest a problem with the
Inverter board or the lamps.
Can you recheck the secondary windings on all three transformers and check any fuses on that board.
Were you ever able to find or make a bulb to substitute in a lamp test.

[woaimi]

Re: need help to test inverter transformer

I desoldered the transformers (all 3) brought it to the guy who works with electronics for all of his career here and asked him to test it out. I couldn't managed to stick around to see how he tested them but he said they are all working properly. There's no fuse that I can spot on the inverter side of the board (it's ps and inverter on the same board)
About testing backlights, it sort of embarrass to say that currently I have only laptop bulbs to mess with and I broke couple of them already from just trying to get it out of it shell, so I was hoping I can find another way to test those bulbs. I will open another old laptop screen and try again tonight, hope I don't break them again.

[budm]

Re: need help to test inverter transformer

OK, it sounds like the inverter was trying to startup (you get about 70V, but more likely to be higher AC signal that your meter cannot handle).
I do want to use the test lamp at this point, I never try with TV inverter yet, I am not sure if your TV uses U-SHAPE or Straight setup, if they are a straight lamps, then there should be small lamp return wires back to the inverter board or may be tied to the chassis some where, you will have to look real close. See PDF for details.
You may be able to use T5 12" LAMP for testing, not sure it will work since I do not try it yet but I will.
http://www.amazon.com/10pcs-F8T5-CW-...words=t5+12%22
Can I get the model number of the LCD panel so I can search for the spec sheet to see what it uses?

[woaimi]

Re: need help to test inverter transformer

I snapped a couple photos of the lcd and the bulb connector, hope they'll help. The connectors are the only thing that are visible from the lcd, I'll open the case when I have a chance. The bulbs connectors mark JST04 10A, the color on those wires are baby blue and white.

[budm]

Re: need help to test inverter transformer

OK, it does not use U-SHAPE tube but the two tubes are coonected in series to form one tube, so there is no ground return wire. You can try hooking up CFL lamp to the Blue and White wires.
See spec sheet of the LCD panel.

[woaimi]

Re: need help to test inverter transformer

should I expect to see the light bulb stay on for as long as the tv is on?

[lilmonk3]

Re: need help to test inverter transformer

Woaimi.. Did ya get anywhere on this set yet??

[woaimi]

Re: need help to test inverter transformer

I'm back...whew! it took forever to get my shower valve replacement from Price Pfister via warranty policy.

Anyhow, I'm ready to get back on the tv again, wonder if anyone has any idea to tackle this problem.

A quick recap of the status at this point:
The screen would turn on a few seconds then goes black, sound still on and I'm able to see the screen with a flash light. It pretty much is a "2 seconds to black" problem. All 3 transformers were replaced with new ones, all components passed the initial tests throughout the whole thread. Any thought is much appreciated.

[woaimi]

Re: need help to test inverter transformer - solved

update.....

While I ran out of things to check and test, I suddenly realized someone's note while I was on the quest to search for a cure (couldn't remember where I read it from) about the Darfon transformer inverters that for some reasons they are extra sensitive to the each other. I purchased 2 of the new 3 transformers from a chinese vendor on ebay and later purchased the 3rd from another vendor in US (to shorten the shipping time). I thought that might be a problem so spent another $10 with the same vendor where I got the first 2 transformers. I got the shipment in 20 days (ridiculously long) soldered it in and ....
VOILA! the set is back to life
thank you everyone for being very patience with me. I picked up quite a few tricks and skills for my own. The family is very grateful. All cost and time are donated.
I already have another tv to work on and will tackle it when I get a chance, so more questions are on the way.