View Full Version : no power?


radio nut
09-20-2014, 12:17 PM
I am "trying" to help a coworker with his lcd tv,
it is an rca Model # L37WD12YX1 40 inch set and he believes it is about 4 or 5 years old.
OK, It has been fine until recently and here is what is does;
It started when you hit the power button and it turned on but with a delay it never had originally. But still functioned great
As time went on it came up slower and slower.
Now the power button lights up but that's it......no sound or picture at all.
just the lit power button.
Any ideas? I am into the antique stuff so this will be my first modern set to look at.

mstaton
09-20-2014, 12:59 PM
Check for bulged electrolytic caps on the PS. That model TV is famous for that

WISCOJIM
09-20-2014, 01:00 PM
https://www.youtube.com/watch?v=YFwfvw29JEU

radio nut
09-21-2014, 07:56 AM
ok, will be getting the tv at my place Tuesday, so I will keep you posted.

powerking
09-21-2014, 09:39 AM
As in the video that WISCOJIM references, many times electrolytics can show no signs of failure externally (bulging, electrolyte leaking, etc). The best tool for "going around the boards" to quickly check them is an ESR meter which works in-circuit; as most all do. They are so cheap now, that IMHO it show be a mandatory test/measurment device right next to a DVM and the soldering iron.

Tom (PK)

radio nut
09-22-2014, 06:33 PM
ok, ESR ? what does this stand for?

WISCOJIM
09-22-2014, 07:14 PM
ok, ESR ? what does this stand for?

http://en.wikipedia.org/wiki/Equivalent_series_resistance

radio nut
09-28-2014, 06:49 PM
Here are some pics

radio nut
09-28-2014, 06:55 PM
The first pic is the main power supply and has at least 4 electro's that are bulged. The second shows what I believe to be the main and the standby board. When I try to turn on the set the signal line reads 5 volts dc....if I am checking the correct wires. The only others I saw are 120 ac volts. The third pic is the mini board and pointing towards the front is the signal line.....someone stop me if I am wrong! Yes the pics are not great but they were done with a cell phone in a dim basement .

radio nut
09-28-2014, 07:05 PM
Just watched video again. So the 5 volts to the mini board signal it to send the 120 ac to the main power supply? If I am stating this correct then the mini board is good since the red/black wires going to the main power supply was getting 120 ac. The main board is the one with about 4 bulging caps.

Username1
09-28-2014, 09:50 PM
If you have bulged caps, replace them all first. Don't even turn it on till you do.

.

Reece
09-29-2014, 04:29 PM
Caps that bulge their tops, even a little bit off of dead flat, need to go. Sometimes they leak out of the other end, though, so look there, too.

radio nut
09-29-2014, 11:52 PM
One thing I do not understand about the ESR meter....
I have seen plenty of times that a cap or electro will test good at low voltage and test bad at closer to rated voltage with a heathkit cap checker when the cap is out of the circuit.
So How is an ESR meter supposed to help when it has a low voltage reference signal?
The bulging caps tested fine with an ESR today over at Fair Radio here in Lima, Ohio.
They Don't sell them but they keep one around for their tech to use.

Zenith26kc20
09-30-2014, 11:36 AM
I have tested ESR on bulged caps and most of the time they will test good. Their capacitance generally goes low. Any bulged cap is suffering from the "capacitor plague".
Never trust one. Also, test any small (47mfd or lower) capacitors on the power supply. Usually LG TV's have the small ones lose capacitance but I've seen almost all of the name brands and some no name have these problems.

radio nut
09-30-2014, 02:10 PM
as soon as I can get the bulging caps out i will order new ones from Moyer's electronics. so far i can't read all of there values and really do not want to assume!

Username1
09-30-2014, 05:20 PM
You better take pictures before taking them out. And they are polarized, so remember
or make sure your pic is clear, close, and shows polarity of each cap you remove...

Don't bother testing something that is bulging, or leaking, it's going bad, it will soon go
POP, so get new ones. A few volts higher rating would be nice....

.

radio nut
09-30-2014, 06:44 PM
I thought about that already, since 3 are 1000 MF@35 and I believe the other 3 all in the same are are 1000mf@16 volts. The only thing that might make it interesting is the area is kinda tight, make make installing higher voltage ones "ugly". A couple of 16 volt are almost touching a heat sink now,35 volt caps would be bigger and hitting it. Now I will admit I see nothing attached to the heat sink so it in this case may be to match the height of the rest of circuit board in order for a cover to bolt on to "something " in this corner so maybe that won't hurt anything.
And with the price of these caps a little experimentation may not hurt

radio nut
09-30-2014, 06:46 PM
its the caps in the first picture i posted.....the only clear pic!

radio nut
09-30-2014, 06:50 PM
I guess one thing so far is a good sign...the fuse on this board isn't blown so hopefully nothing else went bad.
I was told on this site not to even turn it on...which I understand why but I already did because the owner tried for a long time to see if it would ever work so I figured any real damage was already done.
I hope I am not wrong!

Username1
09-30-2014, 08:33 PM
Well you don't have to go to 35v from 16v. You can do 20v, or 25v. And there are times
when going to opposite lead layout and putting some insulation over the leads as you
replace the cap will help the ugliness factor out. Don't forget there can be at least
2 good possibilities for these newer caps going bad. They skimped on the design and used
a 16v cap in a 16v circuit, leaving no margin. or the manufacturer of the caps skimped
and the caps really will not last at the 16v level. Also, if they skimped on the caps, they
most likely skimped on the more expensive parts too, and maybe some of them may not
be available when they fry, so don't outclass this thing with Lexus parts.... The rest of it
may not last....

.

radio nut
09-30-2014, 08:54 PM
one output is 24 volts ....written on bottom of board and the other i "believe" was 5 volts. 24 i am positive but not so sure on the other. I'm at work on break and the board is at home. i am pretty sure there was enough leg room on voltage though. must be poor quality caps.

radio nut
09-30-2014, 08:56 PM
I tried the net and so far this power supply board is not available to purchase, and if it is it's probably not cost effective either!

Username1
09-30-2014, 09:46 PM
Yah, they know the life of the unit as a whole is most likely pretty short.

.

radio nut
10-08-2014, 02:14 PM
well, just yesterday had the time to remove the caps, and sure enough on a heathkit cap checker they tested fine at low voltage and junk at circuit voltage. ordered new ones and now its the waiting game for the new ones to get here.

powerking
10-09-2014, 07:12 AM
Regarding realestate of the caps on circuit boards, most manufacturers have reduced the size of the can over recent years and/or offer a taller profile (same diameter) and at the next higher voltage range (say what was 16V and now is 25V) to give you some more margin. This is why many use the very good parametric search engine features like Mouser and DigiKey have when shopping for components. As others have said, a failed 47uF 16V 85deg-C high frequency switching power supply cap in a 15V circuit is a very poor margin. To me it should be a low ESR, 25V 125 deg-C pro-active replacement type; maybe also upping the capacitance to 63 or even 100uF to get the ESR even lower.

Tom (PK)

andy
10-09-2014, 10:59 AM
For this type of circuit, going up in voltage probably won't help much, and could actually make things worse since higher voltage caps can have higher ESR. You need to use caps that are rated for high ripple current, and low ESR. Also, they must be 105 degree caps. Since space is tight, pay attention to the diameter of the replacements. Often, comparable caps are available in several sizes. Go with name brand caps like Nichicon, or Panasonic. Don't just stick some house brand like NTE in there. You've already seen what happens when they use any old cap...

Findm-Keepm
10-09-2014, 06:11 PM
I've always used 35 volt caps where the originals were 25. With the newer Panasonics, the sizes are the same as the 25 volt versions. At the last Samsung seminar I attended, the reps were recommending the same, as they had run across some 24 volt supplies with 25 volt caps in them -no margin whatsoever. I just finished three Insignias that all had bad caps, and went up in voltage (with a corresponding drop in ESR) on all but the four 16v caps for the 5v/3.3v standby circuit.

My favorite caps are the FC and FM series from Panasonic - where going up in voltage always yields a higher ripple current and lower ESR. 680@25 - .052 ohms ESR, and 1220mA Ripple current. For the same in 35v, the ESR drops to .035 ohms, and ripple current increases to 1815ma.

radio nut
10-21-2014, 11:55 PM
ok, caps came in, put them in the power supply....and nothing. But I am curious the smaller board sends power to the main board. how much AC does it send to the main board? I tried powering it up but the main board has zero input AC. Also, the "mini" board was showing 3. Something DC to the small connector and 125 Ac on the big connector going in .
Even with me hitting the power button the DC to the mini board stayed at 3.4 or so ...Do I have to have a dvd or something hooked up to get it to respond or is something else wrong here?

radio nut
10-22-2014, 12:13 AM
Just watched you tube video link on earlier post for this problem....since the mini board makes the standby power and my standby voltage is low then there is a cap on the mini board that is bad also. correct?

radio nut
10-22-2014, 01:01 PM
i removed the 470mf cap on the standby board and it tested ok on a heathkit cap checker ,but then i got real curious and put it on a digi-bridge and it came up as 32 mf. wow. i put a new 25 volt cap in instead of the 16 volt one that was in there and when i get home after work(second shift) i will try this tv again.

radio nut
10-22-2014, 02:10 PM
so what would cause a 470mf cap to test ok on a heathkit cap checker ,but be way off on the 470 mf part reading only 32mf. is this cap starting to "open"?

radio nut
10-22-2014, 11:59 PM
Well, I put the standby board on and.....drum roll please.....it works! Ya! Gotta put it back together now...but Yeah!!. Thanks for the help!

radio nut
10-23-2014, 12:28 AM
here it is!

ChrisW6ATV
10-24-2014, 12:30 AM
so what would cause a 470mf cap to test ok on a heathkit cap checker ,but be way off on the 470 mf part reading only 32mf. is this cap starting to "open"?
470uF is a large value electrolytic capacitor. I wonder whether such large values can be reliably "measured" on capacitance meters. It is not something I ever tried. Much more valuable with electrolytics is to test their ESR, effective series resistance. That part probably has high ESR, and would be easily identified as bad on such a meter.

Excellent news that you got the set working again!

powerking
10-24-2014, 09:14 AM
You mentioned testing this cap on a "digi-bridge". What is that; perhaps one of those cheapy Chinese digital ESR all-in-one type testers ? I assume that after all this discussion in this thread you did finally get an ESR meter?


Tom(PK)

radio nut
10-24-2014, 09:41 AM
The digi bridge over at fair radio is a every expensive digital bridge for checking values of resistors and caps. Oh,on the ESR ....there were 6 buldged caps on the main power supply board that checked fine with an ESR, but tested junk on a Heathkit cap checker. So for right now I will not get an ESR meter. I have worked on vacuum tube stuff for years, but not modern TV,s. If I want to use an ESR I will just take the board in question to fair radio and use there a.

radio nut
10-24-2014, 09:46 AM
My problem with the ESR is in this case 6 caps tested good, actually the ESR showed the 470 MF cap as good. The american made bridge showed it as only being 32MF after rremoval. So in this case the ESR was wrong 7 times.
now, maybe the esr is a cheap manufactered poor quality meter...that may be the case. if a high qaulity esr would function better then ok, i will have to get one.

powerking
10-24-2014, 09:06 PM
My "guess" is this digi-bridge instrument is just a high accuracy -component out of circuit- only Wien bridge based device. Most all ESR meters out there currently are non-Wien bridge based and use a high frequency test signal (~~ 100Khz sine wave) to effectively measure the A.C. impedance of a capacitor. Also, they only output ~~ 100mV or so in that they don't activate any PN on NP semiconductor junctions; another reason they are so handy for in-circuit testing. Yes the ESR maybe a fraction off in-circuit VS out of circuit but you're looking for a gross discrepancy when using these ESR meters. Take a 100uF cap which measures say 50 ohms and the spec should be less than 0.1 ohms; light bulb event; Houston we have a problem; LOL).

So it's not surprising how you got misleading results on the tested caps in-circuit VS out of circuit on this "digi-bridge" tester; expected behavior??? If I'm wrong, others will "correct" me.

Tom (PK)

radio nut
10-24-2014, 11:43 PM
Thinking about it in all fairness the ESR used only had a good/bad scale and the caps checked did fall on different sections of the good scale. Maybe if I had read the directions or been taught by a professional on its use first then maybe the same value/voltage caps testing (maybe good ) but closer to the bad range would have been a red flag to impending doom. The complaint was that the set would not turn on at all. 6 of those caps were on the main board and would not stop the set from turning on.
Maybe "my" ESR complaint is that I have not gotten the feel for.....or understand how to use it correctly.
the "6" caps were bulged and needed to be replaced .
The 470 mf cap was the one keeping the set from turning on..
So now I am curious, Do the ESR meter owned by members here have a pass/fail scale or are they more advanced?

radio nut
10-24-2014, 11:53 PM
This is the final pic!

ChrisW6ATV
10-25-2014, 02:31 AM
That is an interesting experience with the ESR tester. I have only used ones with an analog meter, marked with a scale in ohms as well as minimum values for "good" capacitors of various sizes. So, a 1000uF part could read nearly full scale but it would be bad on such a scale.

radio nut
10-25-2014, 01:45 PM
maybe this one had an ohms reading and since i did not have the directions or specs on caps, maybe it was showing them as questionable.... need to learn before i make snap judgements!

davet753
10-25-2014, 11:07 PM
When I spent my days troubleshooting, my ESR meter cap checker was the best thing since bottled beer. While it was not 100% accurate, it saved so much time it was worth the occasional false good readings.

Findm-Keepm
10-26-2014, 08:41 AM
When I spent my days troubleshooting, my ESR meter cap checker was the best thing since bottled beer. While it was not 100% accurate, it saved so much time it was worth the occasional false good readings.

Ours paid for itself many times over. It was the one piece of test equipment that never let us down either! 80 bucks to buy, and it saved hundreds of hours of troubleshooting.

Cheers,

ChrisW6ATV
10-26-2014, 09:56 PM
The few times I got a "false good" reading with my ESR meter at work was when I happened to have a capacitor in a circuit with a low-value resistor in parallel, or in a case where several capacitors were in parallel and not all of them were bad.

radio nut
10-28-2014, 10:00 AM
I talked with the person who showed me how to use the ESR......they did not know how to use one correctly!
Live and learn!
I think I will have to get one

powerking
10-28-2014, 11:29 AM
This ESR/capacitor tester has generally been well received for its operation (simply FYI)...

http://www.ebay.com/itm/Peak-Atlas-ESR70-Latest-Version-In-Circuit-Capacitor-Tester-Meter-New-/111492058866?pt=LH_DefaultDomain_0&hash=item19f571cef2

Along with this one:

http://www.ebay.com/itm/Blue-ESR-Capacitor-Tester-Meter-Complete-Kit-for-Assy-/261553292162?pt=LH_DefaultDomain_0&hash=item3ce5ca8382

Tom (PK)