26" Sharp LC-26DV22U LCD power problem.

[Davegerg]

Hi, I picked up a Sharp Aquos LC-26DV22U for $20 at a garage sale. Figured I would find some puffed up caps and replace them for $5. No such luck. I hit the power button and the light turns green on the front. No picture, backlight or sound. I do hear some buzzing noise from the large transformer on the p/s board (CEF273A). After reading that pins 1-5 on the white connector (far left) needed 24v and they only had about 8v, I wondered what would happen if I 'introduced' 12v from a wall wart. Well, I touched pin 1 (red wire) with the 12v adapter and now the TV & DVD work fine! The noise from the transformer goes away, too. Could this transformer be going bad or would another component keep it from working properly? Thanks for any suggestions.

[tom66]

Re: 26" Sharp LC-26DV22U LCD power problem.

Do you hear a slight ticking or clicking sound from the transformer?

Do you ever hear a relay click when the power button is pressed?

[selldoor]

Re: 26" Sharp LC-26DV22U LCD power problem.

Have you tested the small green fuse top of your picture to the left of the yellow barcode label

[Davegerg]

Re: 26" Sharp LC-26DV22U LCD power problem.

The sound I hear from the transformer is buzzing sound (or maybe a sizzling sound). When I power-on, the relay clicks right away. When power-off, there is a 10 second delay before relay clicks.
The green fuse tests good (I did a continuity test with my meter).

[tom66]

Re: 26" Sharp LC-26DV22U LCD power problem.

OK, try unplugging the power connector where you measure 24V and see if it increases.

[Davegerg]

Re: 26" Sharp LC-26DV22U LCD power problem.

OK, With green light on, pins 1-5 measure 8.74v whether connector is plugged in or not. After I 'jump start' it, unplugged they measure about 25.3v. Plugged in, voltage drops about 1/4v. Why would 'jumping' it with 12v for about a second make it work? Some facts I didn't state earlier: all the caps are Rubycon and the set was made in March 2007. Thanks!

[selldoor]

Re: 26" Sharp LC-26DV22U LCD power problem.

Where exactly do you connect the Booster ? 12v+ to pin and what for the ground?

When it doesnt come on can you locate the startup cap in the primary section maybe
50v 68uF and see what voltage it has.

EDIT could be C431 50v 10uF

[Davegerg]

Re: 26" Sharp LC-26DV22U LCD power problem.

I connect the booster pos. to any of the first 5 pins and the neg. to a mounting screw. Doesn't matter which pin - results are the same. The closest cap I could find is a 100uf/100v and it reads .3v - if I'm measuring it right. I put the pos. lead on one side of the cap and the neg. lead on a mounting screw. Did I do that right?

[selldoor]

Re: 26" Sharp LC-26DV22U LCD power problem.

No - just measure across the cap what value is c431 did you miss my edit

What do they measure after you have boost started

[Davegerg]

Re: 26" Sharp LC-26DV22U LCD power problem.

Sorry, I missed it. After I downloaded it then found a rar reader and finally opened it - I realized I already had the schematic printed out! The CEF273A in your doc is a little different than mine. I had downloaded the manual for a LC26SH12U set and it more matches my board. Anyway, I tested the C431 and found the voltage was 19v before my boost and 15.45v after.

[selldoor]

Re: 26" Sharp LC-26DV22U LCD power problem.

Can you get a picture of the back of the board - perhaps a poor joint. In fact
before you do that, while its in the non start stage, try just pressing gently on the board with a stick or piece of plastic just to flex it here and there- try near the connector and around the transformer.
You could also try gentle heat with a hairdryer

[Davegerg]

Re: 26" Sharp LC-26DV22U LCD power problem.

Well, I poked and prodded the whole board. I did notice the sound of the buzzing changed on the transformer when I prodded it. No change to voltages though. I touched each joint on the big transformer with a soldering iron with no results. I didn't try the hair dryer but earlier, I had left the TV on for about 2 hrs to play a DVD. Everything was nice and hot, but still no 25v when I tried to turn it back on. Attached are two pics of the back.

[budm]

Re: 26" Sharp LC-26DV22U LCD power problem.

OK, I look at both power supply diagram, so the switched 24V (PIN1~5) is only putting out about 8V. What do you get at the switched 12V output? The 12V and 24V are generated by the same power transformer, so I expect the 12V output will be really low. So when you attach the external 12V to feed into the 24V line, the backlights and the TV and sounds start working?
And right now you have indicated that the TV is still running with and external power supply attached but you are still not getting the 24V for inverter circuits, that is confusing since the backligts inverter circuits need 24V to operate. May be I do not quite understand what you are seeing as far as the voltage readings you are seeing? How big is this 12V power supply? The 24V supply in the TV is about 4~5A.
I cannot really see how the TV is running off the 12V feeding into the 24V output terminals right now.

[Davegerg]

Re: 26" Sharp LC-26DV22U LCD power problem.

No, I'm not attaching the 12v wall wart permanently. I put a couple of leads on the wall wart and briefly (1 second) touch it to pin 1 on the white 24v connector. This makes that pin (and pins 2,3,4,5) go from 8v to 24v. Then, the TV works fine. It's like I "jump start" it. The only other voltage I've checked it the connector that goes to the DVD. It was about 3v before my "jump start". After, it was 12v.

[Davegerg]

Re: 26" Sharp LC-26DV22U LCD power problem.

When I said I wasn't getting 24v, I meant that after I shut the TV off and then turned it back on, I wasn't getting 24v. Every time I shut off the TV, it won't work when I turn it back on - unless, I jump start it with the 12v AC adapter.

[budm]

Re: 26" Sharp LC-26DV22U LCD power problem.

OK, now I understand, let me see how the circuits work indetails then I may be able to help.
So I can use the LC-26SH12U circuits to analyze the problem? The one that I posted?

[Davegerg]

Re: 26" Sharp LC-26DV22U LCD power problem.

Yes, I'd say that's the right one. Thanks!

[selldoor]

Re: 26" Sharp LC-26DV22U LCD power problem.

Did you replace any caps?- looking at c431 on the back the joints dont look too good.
What make of cap is that? There are other odd looking parts perhaps budm will identify where we should be concentrating on

[Davegerg]

Re: 26" Sharp LC-26DV22U LCD power problem.

C431 is the one you had me check earlier. I did replace it (with no effect) and that's why the joint looks bad.

[selldoor]

Re: 26" Sharp LC-26DV22U LCD power problem.

C431 is the one you had me check earlier. I did replace it (with no effect) and that's why the joint looks bad.

Replaced it with what make/series - should be low esr - can you check the soldering - probably looks worse in the pic than it is but the joints look pretty close together and the trace looks a little lifted.