Our HDTV Just Died...

[leadlike]

We have a Samsung CRT HDTV model #TXN3075WHF. This set was made in '03. Laura had been telling me it was shutting off after running for a while. I only watch a little tv when I get home in the evenings and didn't have a problem with it.

I decided to just let it run for a couple hours, and finally, it went into its failure cycle: shut off, and try to turn on three times before shutting off completely.

It took a couple evenings to figure out how to drag a television that weighs as much as I do into the workroom, and to put it onto a rotating stand to let me move it about as need be.

Opening it up revealed the problem right away-a Samyoung branded cap 250v, 820 uf, was ready to explode. It sits right next to two fat relays that must be the ones I hear when the tv powers up (the first click comes right after I hit power, the second comes five seconds later and that brings audio and video up). I guess the power supply is getting hot and the tv goes into protection after that.

I saw another Samyoung cap of similar construction that seemed to be getting warm during operation. It was in a line of four other lytics so out they went. I always thought this set had kinda flaky HV regulation (I swear the width would change slightly, in the middle of a scene) so I removed the lytics from around the flyback and HOT as well. With a sample of about a dozen caps out now, I set to checking them.

I had three brands-Samyoung, Samsung, and Samwha. Both Samyoung and Samsungs test bad on my Heathkit checker. Samwha caps tested just fine. These were all larger value caps, testing any of the caps that were below 470 uf seemed to be okay.

So I'm gonna stop there. Before I put in an order to Mouser, is there anything else I should be looking for as far as trouble spots in a set like this? I did not fiddle with any of the caps on the neck board, BTW, just the ones on the main board. In spite of the crummy Chinese caps, the rest of the tv looks to be in great shape-no hot spots on the board, etc.

[radiotvnut]

I don't have any experience with this TV; but, the problem does sound cap related and it will probably be OK once you replace the bad caps. Were the original caps of the high temperature type (105 deg. C)? If so, you'll need to use high temp caps as replacements. Even if they are standard 85 degree caps, you'll do better to use 105 degree ones as replacements.

[leadlike]

I was thinking the same thing myself. They are all 85 degree models, but Mouser does offer a 105 degree alternative in the proper case size. Looks like I will have to buy a Panasonic brand cap to replace the nearly blown up one-not so sure on Panasonic quality, but the rest will all be Nichicon lytics.

I noticed that many of these caps are of the same value (ie many are 2200 uf, 50v 85 deg) but they are different brands-wonder what they were up to there? They use the same size case, so that isn't it, maybe different ESR tolerances?

Oh, and I am such a neophyte on color tvs, I have to ask-the flyback transformer does not terminate to an HV clip for the crt, rather it connects to another flyback-looking piece of hardware and then clips to the crt-is this a tripler?

[radiotvnut]

I think Panasonic is a good brand.

That device between the flyback and the CRT is likely a focus resistor. Are there any adjustments on this device and does it have any leads that go to the CRT socket?

[freakaftr8]

Samyoung are crap from the factory! Nichions baby! Or spring for ELNA or SamXon, SamXon's seem to hold up really well! And get a 105c temp rating too. You know how many lytics I see blow or ready to blow in LCD monitors that use these crappy samyoung caps!

[Sandy G]

Shit...In a $1500 tv, it looks like there oughta be enuff profit margin to install DECENT components...But no....EVERYTHING nowadays is Wally-world quality..."Make it last til they get it home..."

[leadlike]

Well, it wasn't a $1500 tv to me-I bought someone a chinese dinner for it. It is an extremely low hours set, and being a crt, I would like to keep it going for as long as possible.

I have about 18 caps out now-so I'll order their replacements today. Again, I do have to credit Samsung for using a decent board-I can solder on it without destroying it, so putting new caps in shouldn't take too long once I get them.

To answer the earlier question, I don't think it is a focus resistor, as it has no controls on it-the focus control is on the flyback itself.

[rca2000]

Originally Posted by radiotvnut

I think Panasonic is a good brand.

That device between the flyback and the CRT is likely a focus resistor. Are there any adjustments on this device and does it have any leads that go to the CRT socket?

That IS a focus resistor--BUT it is for "dynamic focus" I think, and is not adjustable. the 2 focus controls should be on the fly itself.

ALSO--Make SURE you resolder ALL of the connections to the vertical output chip(near the flyback on a sink" and around the fly and H-driver area too--to insure a good repair. I used to fix a LOT of those sets a few years ago. NOt, of course it is nearly all flat-panels.

[ChrisW6ATV]

Originally Posted by freakaftr8

Samyoung are crap from the factory! Nichions baby! Or spring for ELNA or SamXon, SamXon's seem to hold up really well! And get a 105c temp rating too. You know how many lytics I see blow or ready to blow in LCD monitors that use these crappy samyoung caps!

This is good to know... I had read about a specific LCD TV that said it usually has bad SamXon caps, but I found Sam Young caps in mine. I replaced the suspect ones and it works fine.

[leadlike]

I put in the new caps, it took about 20 minutes. It was well worth the time to measure the spaces between the leads on the old caps, as the replacements fit perfectly. Mouser made a mistake and sent me a 100v cap, despite the fact that the inventory number on my order form matches a 160v cap on their site. No matter, I had the cap I needed in my parts pile (nichicon).

I have the tv running now, so we'll see how long this lasts....

[leadlike]

While I have this out, I may as well ask-I do have another minor issue with this set, which I have had since I acquired it:

Hooking up my LD player, or any other SD device using the RCA inputs creates a very faint light vertical line on the screen, which can change its screen position with cycling the power on the external device. Looks like a drive line for want of a better term. Hooking up the external device with coax eliminates it. Problem for me is, especially with my LD picture, using the RCA cables produces a vastly superior picture over plain-jane coax. Since this is an issue I have had with multiple devices, I am sure it is an issue with the set. Any ideas on what it may be?

[Einar72]

It sounds a lot like good old Barkhausen's syndrome to me. In the old days you had to be careful to place the internal twinlead run away from the horizontal section, lest you'd pick a couple up. Could be the "RCA" cable is of poor quality and is picking up some stray signal and feeding it right into the video section.

I'm just hazarding a guess, because when you say coax, are you substituting a good coaxial cable to the RCA inputs versus Wal-Mart stuff, or the RF input versus RCA inputs.

[leadlike]

I've tried various qualities of cables, always with the same results. I did find a query from '04 on a forum where someone had the exact same problem on this set. He only got one response "turn your brightness down". Not too helpful-but it does tell me this happened to these sets when they were new.

I would be impossible to misplace the lead-ins for this set-they are soldered right to the board-no twin leads here.

I think I might have been confusing in how I was describing this-by coax, I am hooking up to the rf input, which causes no interference. Hooking up into the RCA inputs creates this problem

I don't know anything about comb filters, but maybe using the RCA jacks means I am using the tv's comb filter, while using the coax means I am using my LD player's comb filter, and bypassing that part in my tv....

[Wizard256]

There are bulletin on these model and there are one resistor that needs changing and this is located in power supply board. 1/4W 140K resistor, this is only value. Resistor's body telltale color is pink.

Cheers, Wizard

[leadlike]

Replace the pink resistor with a 140K 1/4W? Is this related to the interference problem, or the shutdown problem I was having earlier?