RCA L42WD22 No Picture

[Doming0]

Re: RCA L42WD22 No Picture

The transformers being the rather large rectangular objects on the inverter boards pictured in the post above? Sorry, I am ultra noob. =)

[Doming0]

Re: RCA L42WD22 No Picture

I have found the specs on the transformers used in my tv. Now I am going to try and ascertain if they are good or bad.

http://www.bujeon.com/project/front/...r&menu_idx=546

EDIT: I was going to test them but the spec sheet doesn't give me Primary and Secondary Ohm's ratings to go off of. Any ideas?

[retiredcaps]

Re: RCA L42WD22 No Picture

I was going to test them but the spec sheet doesn't give me Primary and Secondary Ohm's ratings to go off of.

I'm guessing the primaries will be around 1.3 ohms. The secondaries might be around 950 ohms.

Report all the measurments. If the secondaries deviate by more than 3%, it might be defective.

A ring tester makes the testing a lot easier.

Here is a youtube video showing the process on how to measure secondaries

http://www.youtube.com/watch?v=eNuGWBPRGKA

or if you have a ring tester, see this video

http://www.youtube.com/watch?v=HMUazhb0bhc

[Doming0]

Re: RCA L42WD22 No Picture

Ok here's the transformers. Since I can't find a decent (maybe discernable to me would be more apt) schematic. Can someone point out to me which are the Primary and Secondary leads?

Oh and I unfortunately do not have a ring tester. I want one though! =)

[retiredcaps]

Re: RCA L42WD22 No Picture

[QUOTE=Doming0;126013Can someone point out to me which are the Primary and Secondary leads?
[/QUOTE]

If you can't find a diagram to show the two, just do it this way as described in #4

https://www.badcaps.net/forum/showthread.php?t=10419

I believe the secondaries are the ones leading to the ccfl connectors. If you flip the board over and follow the transformer pins to the ccfl connectors, those should be the secondaries.

[Doming0]

Re: RCA L42WD22 No Picture

I was testing the transistors and found 2 bad (no signal) on the Slave Inverter board. They are designated Fairchild 1h28sr FDD 8447L.

[Doming0]

Re: RCA L42WD22 No Picture

The Master Inverter seems ok from tests run thus far. The slave board has an additional bad zener diod.

Question.. should I unsolder the transformers in order to test them? Also, how would I go about checking the multi-legged IC's in the middle of both boards?

Once again, I thank all of you for your help. I'm learning as I go here and hope to one day shed my noob status. =)

[retiredcaps]

Re: RCA L42WD22 No Picture

Question.. should I unsolder the transformers in order to test them? Also, how would I go about checking the multi-legged IC's in the middle of both boards?

The transformers an be tested "in circuit".

For multilegged ICs, look up for the part number datasheet. If it is a FET, test s-g, g-d, s-d for shorts.

[Doming0]

Re: RCA L42WD22 No Picture

Many thanks R.C.

After additional testing it seems the Pico fuse is shot as well. I will test the IC's this weekend. From everything that seems to be wrong with the Slave Inverter and the amount of parts required to fix, would it be better just to order a new one.

The master seems ok but the slave seems fried beyond repair IMO.

EDIT: I needed to switch things up from running tests, so I decided to change the caps in an AOC 17" LCD that a friend gave me off the recycle pile.

Changed 3 caps, and I'm using it right now to type this. =)

[OldNewTech]

Re: RCA L42WD22 No Picture

Same exact problems with the same tv I'm currently working on. The 2 bloated caps on the master inverter board. Replaced those. Transformers look/test good on both boards. Then I jumped over to the slave board and, unlike the master, 25 volts was not going past that smd fuse. So something must have popped it. Found the same 2 smd transistors shorted. Nothing else though.

I just bought a slave replacement from shopjimmy.com, couldn't find the transistors online due to error in reading make/part number of the transistors. Now that you've posted them, I could've gotten them from newark.com for $1 each... damn!.

Will post what happens when the board arrives.

[Doming0]

Re: RCA L42WD22 No Picture

Sounds good O.N.T., keep us posted.

[Doming0]

Re: RCA L42WD22 No Picture

Ok, wow, that took forever and I probably did it wrong! But that's how you learn I suppose.

Anyhow, attached you will find the test results of the Master Inverter Transformers. Please, if you have the time, take a look and see if I'm doing this correctly and what it all means.

Thanks =)

[retiredcaps]

Re: RCA L42WD22 No Picture

Anyhow, attached you will find the test results of the Master Inverter Transformers. Please, if you have the time, take a look and see if I'm doing this correctly and what it all means.

Okay, these tests results don't look right. You have 4 inverter transformers (those black square boxes) in total.

Number them T1, T2, T3, and T4. For each transformer, number each pin any way you like, but make sure it is consistent for each transformer.

For each transformer, you want this these resistance (ohms) test (assuming 8 pins).

1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8,
2-3, 2-4, 2-5, 2-6, 2-7, 2-8,
3-4, 3-5, 3-6, 3-7, 3-8
4-5, 4-6, 4-7, 4-8
5-6, 5-7, 5-8,
6-7, 6-8
7-8

You should have 4 sets of the above readings.

[Doming0]

Re: RCA L42WD22 No Picture

Ok, thank you RC.

What I did was redundant I suppose, since I measured everything 8 times on each of the two Master transformers.

(The inverter is split into two separate boards on my tv Master and Slave and each has two transformers)

So I believe I do have all those results for the first two, I just have to reorganize the data. Then I can test the Slave transformers with the formula you showed me.

BTW I am using a digital auto ranging multimeter set to ohms. Should I be using the diode or continuity test instead?

[retiredcaps]

Re: RCA L42WD22 No Picture

BTW I am using a digital auto ranging multimeter set to ohms. Should I be using the diode or continuity test instead?

Put the dmm to ohms.

[retiredcaps]

Re: RCA L42WD22 No Picture

http://www.bujeon.com/project/front/...r&menu_idx=546

If you haven't retested the transformers, number like the above url.

I beleive NS is secondary is the URL above.

[Doming0]

Re: RCA L42WD22 No Picture

Ok, here we go again. Just finished up following the same diagram as in the url stated.

Attached you will find the testing done for all 4 transformers.

[retiredcaps]

Re: RCA L42WD22 No Picture

Attached you will find the testing done for all 4 transformers.

The transformer numbers look consistent, however, the only potentially strange readings are the 16 ohm ones.

This transformer test doesn't find shorted turns. A ring tester will find that.

[Doming0]

Re: RCA L42WD22 No Picture

Unfortunately I do not have a cool ring tester.. would you know where to get one on the cheaper side?

Regarding the 16 ohm readings, they may be strange but they are also consistantly strange across all 4 transformers. I wish I knew what it meant! lol

[PlainBill]

Re: RCA L42WD22 No Picture

Unfortunately I do not have a cool ring tester.. would you know where to get one on the cheaper side?

Regarding the 16 ohm readings, they may be strange but they are also consistantly strange across all 4 transformers. I wish I knew what it meant! lol

The numbers are interesting, but I don't see any indication of how you numbered the pins. Further complicating the issue is the lack of clear pictures showing the ends of the transformer. I've marked up one of the pictures and would like some points cleared up. One problem is none of the readings fall into the range I would expect for secondary windings. I would expect the secondaries of the transformers to read in the range of 1K - 2K ohms. 16 ohms implies a much heavier wire than I have seen on an inverter transformer.

For starters, I have marked 'terminals' 1A, 3A, 4A, 5A and 7A. These may be wrap points for the windings, or they might be soldered to the circuit board. The pictures aren't clear enough to be certain. Visually, are they soldered to the circuit board? Resistance readings are not necessary.

On the other end of the board we have more confusion. We have 4 pins on each of two transformers, but only two obvious output pins. What is worse, from the pictures it appears all pins are soldered to a common plane, which makes very little sense. To illustrate, Pin 1 is very obviously soldered to one plane. Pins 2 and 3 are obviously soldered to a different plane. Pin 4 is soldered to a third plane. Also obviously the center two pins of the lower transformer are connected to the center two pins of the upper transformer. It appears likely that the upper left pin of the lower transformer is connected to pin 1 of the upper transformer; certainly all of these planes have features which suggest they handle power - drive to the transformer windings.

Which pins on the right side of the transformers are visually connected together?

The next step is more complex. Set your DMM to the resistance scale. Put one probe on point 14 - one lead of the output connector. What are the resistances to points 5, 6, 7, 8, 9, 10 ,11, 12. If any of these read open (greater than 1 megohm), repeat using point 13 as the reference.

Background - I have seen at least one design that appeared to use a two stage inverter. A high voltage section sat on the power supply, wires ran to transformers mounted at the CCFLs. So, could you post a single - over-all shot of the back of the TV?

PlainBill