Fixed my LCD, tried to make it better - AVS Forum
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Old 06-11-2011, 09:59 PM - Thread Starter
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The caps on my LCD's power supply board failed, so I need to replace them. The board came with a pair of 1200uf, 35v caps, I replaced them with a pair of 2200uf, 50v caps. I asked the guy at radio shack if that was fine to add the extra capacity, he said it should be fine. I remove the old ones and add the new ones, put the tv back together and plug it in. I hear this like beeping, warning sound coming from the board and the tv won't turn back on. Anyone know if adding the large caps is not jiving with the power supply board?

The tv in question is a Magnavox 32MF231D/37.
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Old 06-11-2011, 10:42 PM
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Nothing wrong with that u did, there maybe other problems.

p.s.: Correct polarity? Did not damage any trace during de-soldering?
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Old 06-12-2011, 12:40 AM
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The issue may have been damage done to one of the IC circuits on board from not correctly discharging the entire system prior to opening and working on the board. you did verify polarity of the caps, right?

You need to determine what caused the caps to fail and how did you check the circuit and the caps?

Good rule of thumb in the future though, NEVER take what a Radio Shack sales person tells you as technically accurate gospel.
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Old 06-12-2011, 07:59 AM - Thread Starter
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Quote:
Originally Posted by Gizmologist View Post

The issue may have been damage done to one of the IC circuits on board from not correctly discharging the entire system prior to opening and working on the board. you did verify polarity of the caps, right?

You need to determine what caused the caps to fail and how did you check the circuit and the caps?

Good rule of thumb in the future though, NEVER take what a Radio Shack sales person tells you as technically accurate gospel.

I made sure that the polarity was right a couple of times, because I know that is going to screw the entire board up.

Well I had problems before I opened the set up. The tv would flash about 3 or 4 times before it would stay on. After that the screen wouldn't turn on, the green power light just kept blinking. Searched on-line and found it out it was likely a cap that failed. Opened it up and saw that two of the caps were bulging and had some black discharge on top. I have seen that bad caps are a very large problem with Philips sets made at the time mine was.
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Old 06-12-2011, 09:32 AM
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If the caps are bulging that is USUALLY a sign that unregulated DC voltages from a power supply have exceeded the caps working voltage.

In a linear supply, (full or half wave, transformer-supplied AC rectified to DC) the possibility exists that the rectifier itself could have failed and the caps are getting AC as opposed o DC and you will likely see exploding caps.

The supply in your system is an SWPS so the regulation is the most likely issue. That may well also be the cause of the failure now to turn on. Other components may well be trashed.

As for simply increasing the capacitance and working voltage from the original ratings, the first response to you was correct. INCREASING the ratings will not have an adverse affect on the circuit. In an audio path scenario, yes but not in a power supply.
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Old 06-12-2011, 10:26 AM - Thread Starter
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Quote:
Originally Posted by Gizmologist View Post

If the caps are bulging that is USUALLY a sign that unregulated DC voltages from a power supply have exceeded the caps working voltage.

In a linear supply, (full or half wave, transformer-supplied AC rectified to DC) the possibility exists that the rectifier itself could have failed and the caps are getting AC as opposed o DC and you will likely see exploding caps.

The supply in your system is an SWPS so the regulation is the most likely issue. That may well also be the cause of the failure now to turn on. Other components may well be trashed.

As for simply increasing the capacitance and working voltage from the original ratings, the first response to you was correct. INCREASING the ratings will not have an adverse affect on the circuit. In an audio path scenario, yes but not in a power supply.

Not really what I wanted to hear. I know that there has been been caps made in the last decade, and that is part of the failures. Other bad parts would be why philips has been sued, but not really helping me if I need to buy a new $100+ board.
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Old 06-12-2011, 03:12 PM
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Just a word on increasing capacitor values. It is not always safe to increase capacitance. For one thing, the extra inrush current when it first charges may cause problems.
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Old 06-12-2011, 04:40 PM
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Try to procure a service manual. The blink/noise/flashes etc are feed-backs of what's wrong with the boot up process.
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Old 06-12-2011, 04:53 PM
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Quote:
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Just a word on increasing capacitor values. It is not always safe to increase capacitance. For one thing, the extra inrush current when it first charges may cause problems.

His choice of increase value caps was not way beyond the safe zone and it also depends on the rest of the circuit design. If he had gone from 1500uf to 4700uf or higher I might have a bit more concern, but 1500uf to 2200uf should pose no issue.
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Old 06-12-2011, 11:32 PM
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Quote:
Originally Posted by Gizmologist View Post
If the caps are bulging that is USUALLY a sign that unregulated DC voltages from a power supply have exceeded the caps working voltage.
That, or the caps are part of the capacitor plague problem.

Unfortunately the bad caps can cause other problems in the circuit that can't always be resolved simply by replacing the caps.
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Old 06-13-2011, 10:15 AM
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I have not run across electrolytics failing en masse as suggested in 40+years.
If there has been a rash of these has anyone seen industry documentation as to the company producing them and the cause?

I would be interested seeing actual testing lab data as opposed to the audiophile magazine "expertise". I like provable facts.
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Old 06-13-2011, 02:59 PM
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Quote:
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If there has been a rash of these has anyone seen industry documentation as to the company producing them and the cause?

I read about this a long time ago. It was an industry source but I don't remember which. There was some industrial espionage going on. One manufacturer (Chinese?) stole what it though was a competitor's formula for electrolyte but didn't get it right. The formula they used resulted in early failure of the electrolytic caps. A number of big electronic manufacturers got bitten.
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Old 06-13-2011, 07:46 PM
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Tainted milk, dangerous toys, chemical-laced drywalls... I guess this should surprise no one.
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Old 06-13-2011, 07:59 PM
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MrBobb, let's not forget the melamine in the dog food.

I've replaced countless computer motherboards and power supplies because of bad caps. Even Apple had a rash of counterfeit Nichicon caps in some of their systems.
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Old 06-14-2011, 01:10 PM
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Counterfeiting of electronic components is a huge problem. It takes many forms. It can be relabeling authentic parts to look like higher performance versions, selling authentic used parts as new, selling new fake lookalike parts of similar but usually lower performance, or relabeling used parts with the same form factor and number of pins as something entirely different and selling them as new. Guess what happens to much of the electronic equipment that gets recycled. It goes to places like India where they bake the parts off the PC boards and recycle them in one of the ways above. The process alone generates lots of carbon emissions, toxic waste, and health consequences. Better it should go in the local land fill.
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Old 06-14-2011, 01:20 PM
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Just want to add... may want to buy GENUINE batteries (Japan/Korea good) for your electronics.

I went through 3 laptop batteries from China, they ARE CHEAP. 2 failed, the 3rd one am on now is dying after 150 charge cycles, they usually last like 500 cycles. My genuine Motorola cellphone battery I had since 2006 just started to show old age after 5 years So if u want it cheap, as long as u don't expect them to last.
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Old 06-14-2011, 01:28 PM
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Old 06-14-2011, 01:30 PM
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...buy GENUINE batteries ...

A good idea. But how do you know they are genuine when even the distributors cannot tell?
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Old 06-14-2011, 03:21 PM
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Quote:
Originally Posted by Colm View Post

I read about this a long time ago. It was an industry source but I don't remember which. There was some industrial espionage going on. One manufacturer (Chinese?) stole what it though was a competitor's formula for electrolyte but didn't get it right. The formula they used resulted in early failure of the electrolytic caps. A number of big electronic manufacturers got bitten.

It affected ABIT pretty badly and a class action lawsuit was brought against them (even though they weren't the originator of the bad caps) and ABIT went out of business because of it about 5-7 years ago.
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Old 06-22-2011, 01:58 PM
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http://en.wikipedia.org/wiki/Capacitor_plague

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