Anyone know how to weld a TV circuit board?

[coeceo.livejournal.com]

I'm looking for anyone who is savvy with TVs, Computers, or other electronics and can replace a capacitor on the power board for my plasma TV.

I have isolated the problem, and removed the board, now I need someone who knows what they are doing to take a look and replace the part. Does anyone have this skill, or can anyone recommend a good repair shop that wont totally rip me off on what should be a 20 min job to replace a $1.84 part?

Comments

[geekpixie.livejournal.com]

Random question, wouldn't happen to be a Mitsubishi, would it?

(we had a cap go in the same spot, and it's apparently a well known problem)

[tober.livejournal.com]

Failure of certain capacitors in electronic products is an industry-wide problem. Specifically, the large cylindrical capacitors that can be found in the power supply section of most devices that are powered from utility power are somewhat failure-prone. These capacitors are known as electrolytic capacitors, they contain a moist paste material sandwiched between a pair of plates (the plates are rolled up into a cylinder). Their purpose is to "smooth out" the periodic fluctuation in the pulsating direct current that is obtained inside power supplies by rectifying the alternating current from the wall outlet. Certain (usually) undesirable characteristics that are inherent to these capacitors cause them to heat up in operation. The heat eventually dries out the paste and this degrades the operation of the capacitor until eventually it may cause the device it is in to malfunction. Unfortunately, it's also reasonably common that when such capacitors fail the cause other components to fail as well, so even when the root cause of the problem is just a capacitor, after the failure occurs, one often finds that several components need replacing.

Anyways, yeah, that was a long way of saying "This is a general problem in electronics and is not particularly unique to a certain brand or model or type of device"... although, that being said, some devices are better designed to resist this failure mode and others... not so much :)

[perspicuity.livejournal.com]

there was a rash of such caps that failed during a certain period of time. they showed up in EVERY kind of device. they were amazingly short-sheated in terms of specs, because the makers figured they could get with the it and make profits. they probably did.

have had a few devices fail, and replaced them with hopefully overstudly variants, and all is good again. once, at 2am, in the middle of a movie :) success!

#

[tober.livejournal.com]

Components on printed circuit boards, in general, are soldered, not welded. Is the capacitor in question a through-hole component (i.e.- it has wire leads that go through holes in the circuit board and are soldered on on the opposite side) or is it a surface mount component (i.e. - it has short, splayed leads that are soldered to the same side of the circuit board as the component itself is on)? In general, the former are super easy to do and the latter are somewhat harder although by no means impossible. I would be happy to do it for you if it's through-hole (I do have a good temperature-controlled soldering iron and appropriate solder), although there are certainly more qualified people (I work in the electronics industry however when I need to solder something in the course of my work I usually have someone else whose job is specifically circuit board rework do it).

It depends...

[nvidia99999.livejournal.com]

I've done a lot of soldering in my home electronic shop (my hobby). If it's just replacing a capacitor on a PCB, that should be very easy (unless there are sensitive ICs on the board right adjacent to the capacitor). One question, though. I assume you think it's that capacitor because you can see that it's damaged (broken casing, or black spots on it). But it could be that other components went too, as a result of the capacitor failure. Do you have the replacement capacitor?

[mrpet.livejournal.com]

um,

Speaking as an electrical engineer here. You do realize that caps hold their charge for quite a while, right? If you are working in the power supply section of a high power piece of electronics you can get seriously hurt. At least you were not in a tube based TV, the flyback circuit can get to 30,000V and zap you real hard. I had a friend lose the use of his arm for the day by getting zapped by those voltages. I do not know the exact power supply needs for a plasma TV but each cap has a voltage rating on the side and that can tell you how much trouble you could have been in.

Also unless you wore a static strap tied to ground you could have zapped and destroyed any number of solid state components when you removed the board. Newer power supplies are all digital controlled and if they are damaged they can take out the rest of the HW real quick. You do not need to feel a static shock to have done the damage.

My question to you is how did you do the failure analysis? If the cap blew and vented it may not be the caps fault for doing what it was designed to do. Other circuits could be contributing to the issue.

[boblothrope.livejournal.com]

What's the correct safe way to discharge a capacitor before working on it?

[tober.livejournal.com]

Place a resistor (recommended value something on the order of 100 ohms) across the terminals of the capacitor for a minute (in actual fact something considerably less than a minute is usually required), then measure the voltage across the capacitor using a multimeter and make sure that it is approximately zero.

[Alternately, short the terminals of the capacitor together with the blade of your screwdriver. That's actually the wrong way for a variety of reasons, but many working technicians have been witnessed to do it.]

[squirrelitude]

The wrong way is the *fun* way!

[mrpet.livejournal.com]

do the math, a 100 Ohm resistor across a big cap is just like the screwdriver case. discharge time for a 100uF cap and 100Ohm resistor (at 5-TC is 50mS) Now determine how many joules is in the cap and what that means for current when it is all over in 50mS :)

If you are force discharging caps please put on safely glasses. I was right by someone at work when it was done accidentally and he now has mirrored safety glasses as a souvineer. It saved him from being blinded when the plasma from all of the leads hit him in the face.

[mrpet.livejournal.com]

The wrong answer is to short the leads :) That way leads to suffering...

you can bleed off the charge with a mega-ohm resistor to ground safely; that is why static straps are usually 1MOhm. It all depends on the voltage and the size of the cap. For instance if the cap had a megavolt on it that mega-ohm resistor would have an amp going down it at first; high voltage static straps are usually much higher than 1MOhm or the engineer could be killed if they touched something.

If the cap is really large it can take a really long time to discharge. Time constant of a R-C circuit is conveniently R*C, that is the time to get to 1/e of the final voltage. so if the cap is 10V, 10uF, and 1MOhm resistor would give 10 seconds to get to 3.38V A good rule of thumb is to go for 5 time constants or 50 seconds in the above case.

I know of a lot of people that work on things "hot" but they know what they are doing and use special soldering irons that are not grounded. A regular iron touched to a decently sized charged up cap will instantly discharge the cap through the iron and the cap lead will vaporize and turn into a plasma - not that I have _ever_ done this you see :)

[solarpanda.livejournal.com]

On a side note, being an electrical engineer myself, it always amazes me how many ways you can kill/maim yourself with electricity...

[mrpet.livejournal.com]

A 9V battery has enough oomph in it to kill a person. All it takes is a chopper, couple of caps, a transformer, and two sharp probes and BAM. This is what a Tens unit is, well pads instead of the death probes but you get the picture.

In additional to being a EE I am also in the BDSM scene and the stuff people are playing with *shudder* some people are pretty safe but the rules of thumb I see bandied about are just crazy. A medical grade tens unit powered by a 9V is sufficient to rip your quad right off the bone *dance froggy, dance I say*

When I was a kid I used to test 9 V batteries

[nvidia99999.livejournal.com]

with my tongue...

Re: When I was a kid I used to test 9 V batteries

[mrpet.livejournal.com]

it's the gateway thrill, next thing you probably were abusing roller coasters and then on to the really heavy stuff!

Re: When I was a kid I used to test 9 V batteries

[nvidia99999.livejournal.com]

LOL. Could be, could be! :)

[mrpet.livejournal.com]

try stripping phone wire with your teeth...after someone tried to help by plugging it in for you ;) 48V DC isn't too pleasant across a tooth. Good thing it didn't ring that is over a hundred VAC

I can help with the soldering

[artguychris.livejournal.com]

I can help out with this, but not until after the holiday weekend. Some night later next week would be OK. Send me a PM with your contact info.

Do you have a replacement part?

If you didn't kill yourself removing the board, it's probably safe, but probably best not to handle it with bare hands. Put it in one of those shiny anti-static bags if you have one. I have a meter so we can check & bleed off anything dangerous.

Thanks

[coeceo.livejournal.com]

Thanks for all the responses. I took it into a repair shop and will suck it up and pay the $50 diagnostic fee and nominal capicitor/shipping charges.

We will see if this fixes it, if not, I may take artguychris up on his offer.

Other info for those who are interested. This is a Philips TV but similiar issues are in other brands with the same guts. Apparently both their plasmas and LCDs have a known issue with under rated capacitors and other problems that result in fried TVs anywhere from 1-3 years from purchase. Search "philips blinking red light" and you will get a ton of horror stories about this problem. Some have been able to fix it, some not, all with no help from the manufacturer. Lesson for me is to get the 5-year protection on my next one. They just don't build them like they used to.. good 'ole cathode rays.