RCA L42WD22 No Picture

[Doming0]

Re: RCA L42WD22 No Picture

Hi PlainBill,

I have attached some hopefully better pictures for you.

In regards to the pins you labeled with the (A) designation, they are not soldered to the board. In my previous testing I left those alone, and only tested the soldered connection. I labeled as it shows in the manufacturers link.


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

As for the right side of the transformer, it doesn't see that any of the pins are visually connected together.

I will do the testing you asked for and post the results.

[Doming0]

Re: RCA L42WD22 No Picture

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.

I measured using your diagram and formula. My readings across all pins were 0.1 ohms.

[PlainBill]

Re: RCA L42WD22 No Picture

I measured using your diagram and formula. My readings across all pins were 0.1 ohms.

The second picture makes that obvious. Right now my brain is spinning like a top. I guess this may make sense. Two inverters, running 180° out of phase. Less chance of a short in a transformer.

The link to the pin numbers seems to be broken.

PlainBill

[Doming0]

Re: RCA L42WD22 No Picture

Here's the diagram from the vendors site.

[OldNewTech]

Re: RCA L42WD22 No Picture

Got the slave board from ShopJimmy today, popped it in and all is good. LCD backlight is now firing up and TV is at 100%. Your readings from the ballast transformers were the same as mine from the primary and secondary. 16ohms and 1ohms.

Good Luck!

[Doming0]

Re: RCA L42WD22 No Picture

Got the slave board from ShopJimmy today, popped it in and all is good. LCD backlight is now firing up and TV is at 100%. Your readings from the ballast transformers were the same as mine from the primary and secondary. 16ohms and 1ohms.

Good Luck!

You are now getting my hopes up! lol That's awesome mate!

I have been very busy with work lately and haven't had the chance to tear into my tv's problem further. I will keep you all posted and may just order a replacement board because it seems all the components on the slave are toasted.

[OldNewTech]

Re: RCA L42WD22 No Picture

Well, if I could see the part numbers clearly on those transistors, I would've just ordered those for a dollar a piece from newark. But would not know the actual part number for that surface mount fuse, but would've found something. From my searching, shop jimmy had the best price for the slave board. About 60 dollars with shipping.

[Doming0]

Re: RCA L42WD22 No Picture

Just to update, still waiting on the inverter boards I ordered. The package has been sitting in customs for the last 10 days. Arrgghhhh....

[Wizard]

Re: RCA L42WD22 No Picture

On these type of panel with that those master/slave inverters. When mosfet transistors goes, the driver ICs fry as well. Main reason for this is bad caps.

Cheers, Wizard

[PlainBill]

Re: RCA L42WD22 No Picture

On these type of panel with that those master/slave inverters. When mosfet transistors goes, the driver ICs fry as well. Main reason for this is bad caps.

Cheers, Wizard

Wizard, glad you again have the time to appear here. There have been too many times when I was wondering WWWS (What Would Wizard Say).

PlainBill

[Doming0]

Re: RCA L42WD22 No Picture

My package has been sitting at customs for 16 days now.... =(

[Doming0]

Re: RCA L42WD22 No Picture

Hey hey!!

After waiting a month for customs to do their job.... the parts arrived.

Installed new inverters... is working!!

I would like to thank all of you that have helped me along the way. It is greatly appreciated!

[Fodder4Thought]

Re: RCA L42WD22 No Picture

So, perhaps I'm missing something - when you guys tested your transformers, was the 16 Ohms what you got from the bad boards, or what you should have gotten from a good board?

I ask because I've got the same TV and am experiencing the same problems (LCD has image, but backlight won't come on). I used a multimeter to test the inverter boards, and on the slave board I discovered that the transistors had differing values both from each other (on the slave board), and from the master board (all four transistors on the master board had the same value, or close to it). In addition, there's a small component that I think is a fuse on the slave board that has high resistance (1+ MOhm), but its analog on the master board has a very low resistance (0.1 Ohm). The transformers on both boards had values of ~16 Ohms between the same pins on all four transformers, and 1+ MOhms between the others.

I ordered a replacement slave inverter from shopjimmy that arrived today, but when I installed it I got ... bupkis. The board layout is different from the original (at least to my untrained eye), and some of the measurements are different, too.

I'm kind of at a loss - can you help?

[retiredcaps]

Re: RCA L42WD22 No Picture

In addition, there's a small component that I think is a fuse on the slave board that has high resistance (1+ MOhm), but its analog on the master board has a very low resistance (0.1 Ohm).

Fuses are marked on the PCB with the letter "F". It will be something like F101. A good fuse will measure less than 1.0 ohm.

[PlainBill]

Re: RCA L42WD22 No Picture

So, perhaps I'm missing something - when you guys tested your transformers, was the 16 Ohms what you got from the bad boards, or what you should have gotten from a good board?

I ask because I've got the same TV and am experiencing the same problems (LCD has image, but backlight won't come on). I used a multimeter to test the inverter boards, and on the slave board I discovered that the transistors had differing values both from each other (on the slave board), and from the master board (all four transistors on the master board had the same value, or close to it). In addition, there's a small component that I think is a fuse on the slave board that has high resistance (1+ MOhm), but its analog on the master board has a very low resistance (0.1 Ohm).

I ordered a replacement slave inverter from shopjimmy that arrived today, but when I installed it I got ... bupkis. The board layout is different from the original (at least to my untrained eye), and some of the measurements are different, too.

I'm kind of at a loss - can you help?

I'm not sure. Do you have a camera? Are you capable of following the links in my signature (post #43) and providing good quality pictures (top and bottom) of the master and slave inverters?

PlainBill

[Fodder4Thought]

Re: RCA L42WD22 No Picture

I'm not sure. Do you have a camera? Are you capable of following the links in my signature (post #43) and providing good quality pictures (top and bottom) of the master and slave inverters?

PlainBill

I sure hope so.

Attached are photos of the tops of the boards.

[Fodder4Thought]

Re: RCA L42WD22 No Picture

As I look at the pictures, I notice that not only are the layouts of the two slave boards different, but the fuses are different too - the original was 10A @ 125V, but the new one seems to be 8A @ 60V. Is this normal?

[PlainBill]

Re: RCA L42WD22 No Picture

As I look at the pictures, I notice that not only are the layouts of the two slave boards different, but the fuses are different too - the original was 10A @ 125V, but the new one seems to be 8A @ 60V. Is this normal?

Well, it's hard to be sure because the camera angle obscured the part numbers, but those appear to be two different boards (LC420WX7 vs ????WX5). The glare doesn't help either.

PlainBill

[Fodder4Thought]

Re: RCA L42WD22 No Picture

Well, it's hard to be sure because the camera angle obscured the part numbers, but those appear to be two different boards (LC420WX7 vs ????WX5). The glare doesn't help either.

PlainBill

Sorry about the photos - I'll try again when I get home and can put the boards under better light. I'll also get pictures of the undersides.

The replacement board came from shopjimmy, and the website claims that it's the compatible replacement board. Looks like the website's picture, too.

[PlainBill]

Re: RCA L42WD22 No Picture

Sorry about the photos - I'll try again when I get home and can put the boards under better light. I'll also get pictures of the undersides.

The replacement board came from shopjimmy, and the website claims that it's the compatible replacement board. Looks like the website's picture, too.

It may be. Or it may not be.

In a nutshell, here is the problem. Two Gorges Electronics in China designs a 42" LCD TV. They produce a few prototypes and offer them to several importers. 'Worst Buy' says they will buy 1000 with an Unsignia label. Two Gorges orders the parts to build 2000 and continues to pitch the product. Technicolor SA comes along and orders 2000 with an RCA label. Two Gorges orders the parts to build another 2000. One of their suppliers says 'So sorry, that inverter not available, we have new part. Works better, just have to remove diode on main board.' To speed delivery of Technicolor's order, Two Gorges starts to build the TVs using the old inverter. When the new inverter comes in, they switch to the new ones, and make sure the main boards are correct. POSSIBLY the label indicates a different revision level, but don't count on it.

The result in is you have 2000 TVs, but some of the parts from the early production are not compatible with those from late production. And NOBODY pays attention to revision levels, even though supposedly identical boards show little resemblance to one another.

That doesn't even begin to consider the problems possible in ShopJimmy's operation. One horrendous example of what can go wrong occurred at the company I worked for about 30 years ago. (This might be boring, quit now.)

The circuit board stockroom had about 50,000 circuit boards on hand. They had a number of problems due to poor control techniques, so a former Chief Petty Officer (Bob) was placed in charge. It took him 6 months to get the place squared away. Obsolete boards were either updated or scrapped. An accurate count of all product was made. They started using a triple entry system to keep track of inventory and location. Two were on hard copy, the part numbers and quantity information was kept on a computer. Any stock pulled or added was initialed by the person doing the work. As a result, anyone could look up a board number, go to the corridor, bay, and shelf indicated and expect to find that number of boards there. In addition, anyone could go to a particular shelf and find a card which indicated the number of boards on the shelf, and who had placed them there, and who had removed boards.

Bob made it known that he would be checking shelves, and there would be fireworks if the numbers on the computer, the history log, the shelf card, and the the boards on the shelf did not match. After the workers figured out Bob was serious, and especially when they learned the new system was easier (no hunting for boards which SHOULD be in a certain bay) things ran very smoothly and calmly.

Things went to heck when management decided Bob's talents were required elsewhere, and the stockroom was placed under the control of accounting. Accountants know how to count, and manage inventory, right? The first thing they changed was to get rid of the triple entry system. 'We'll do it right the first time'. The number of boards was kept on the computer. The location of the boards was kept in the history file. When a new batch of boards was received, they were stored on the first available shelf, and the location entered in the history file. As a result, one shelf could have multiple kinds of boards, and when pulling boards it might be necessary to go to several shelves to find enough. The folly of that approach was becoming obvious when I left the company, but I heard that it got REALLY bad within 2 months. Quantities in the computer did not match the history log, locations were wrong, you name it, it went wrong.

PlainBill