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Replacing bad capacitors in PSU for HDTV

atrix415 1,232 237 March 29, 2012 at 03:37 AM
Many thanks to everyone ahead of time for any help.

Problem: I recently received a half-broken tunerless HDTV (works when it wants) with the MLT386X power supply. The first thing I did was open-up the psu from advice at avsforum.com and noticed alot of caps have leaked and few with bumps.

About Me: This is my very first attempt to fix the psu. I have very litter soldering experience.

So far what I did, purchased

2x CapXon C634 - 1000uF, 10v > 2x NTE VHT1000M16 - 1000uF 16v
2x CapXon C632 - 470uF, 16v > 2x NTE VHT470M16 - 470uF 16v
1x CapXon C618 - 470uF, 25v > 1x NTE VHT470M25 - 470uF 25v
2x Decon 470uF 35v (unsure if these are electrolytic caps and frys has no stock)

I hope that I can fixed it and used it as a monitor for my desktop. (Flight Simulator)

My hdtv model is: Viore LCT37V66HM (uses LG/Philips Display)

1) Picture of the MLT386X (heat-sink removed and exposing caps)


2) Description of each leaking caps.





3) Found some replacement parts at local fry's electronics. (I have a acct at digikey.com but fry's electronics was a 20 minutes drive.)

15 Comments

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#2
Wow that looks like a lot of bad caps. I did this once for a HDTV and it was not to bad, one big thing is make sure you unplug the tv and keep it unplugged for a few days as there can be a lot of left over power in the psu. Also caps are directional so make sure you put them in the correct direction. I know with the samsung I went to a high temp cap (120f vs 80f?) and I think a higher v? since the ones they used where a little under power.
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#3
hi,

I am going with all high temp 105c, low esr (instead of 85c, low temp). I left it unplug overnight (someone said, 15 minutes discharges the ones I have) but overnight just incase. thanks


Any beginner advice?
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Last edited by atrix415 March 29, 2012 at 06:09 AM
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#4
couple of suggestion for you:

1. if you have say 5 caps of the same make/rating and only 2 of them are bulging/leaking and the other 3 look ok, go ahead and replace all 5 anyway.

2. http://www.badcaps.net/forum/ is an excellent source of information on this topic, and his store is an excellent source for replacement quality caps.

3. I've also had good results getting capacitor kits from here:
http://lcdalternatives.auctivacommerce.com/

Good luck with your project!
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#5
Quote from davepry View Post :
couple of suggestion for you:

1. if you have say 5 caps of the same make/rating and only 2 of them are bulging/leaking and the other 3 look ok, go ahead and replace all 5 anyway.

2. http://www.badcaps.net/forum/ is an excellent source of information on this topic, and his store is an excellent source for replacement quality caps.

3. I've also had good results getting capacitor kits from here:
http://lcdalternatives.auctivacommerce.com/

Good luck with your project!

I think I will replaced all the caps. But what are these with caps wrap in heatshrink or something? The caps in blue also looks fine with no leaks, bulging.
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#6
Quote from davepry View Post :
couple of suggestion for you:

1. if you have say 5 caps of the same make/rating and only 2 of them are bulging/leaking and the other 3 look ok, go ahead and replace all 5 anyway.
100% agreed unless you want to be opening it back up in a couple months.
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#7
yes replace all the caps you can..... provided there aren't hundreds.

not sure what that wrapping is for.... or the gunk between them all (unless it's designed to act as a bulking agent to provide support)
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#8
First try practicing on some junked circuit boards that have at least as many layers of copper as the HDTV boards do. BadCaps.net has a FAQ about soldering and desoldering, and there are message threads about this, too. You need an iron with adequate power, and desoldering typically needs more power than soldering does. 40W is usually good for single- and double-sided boards, while 45-50W is better for 4-layer boards. Ironically, using an iron with too little power is more likely to cause heat damage because it takes so long to melt the solder. A chisel-shaped tip works better than a cone-shaped one, but the most important thing is to keep the tip clean (wipe after each joint) and well-tinned.

Most electronic devices are now made with lead-free solder (probably "RoHS" printed on the board), which needs more power to fully melt it, and many technicians recommend applying some regular 60% tin, 40% lead solder to each joint before trying to desolder. Even better is 63% tin, 37% lead eutectic solder.

I'd rather not use NTE brand capacitors because they're not exactly the finest. Panasonic from Digi-Key, Rubycon or Nichicon from BadCaps.net, Mouser or BDent, or Sanyo/Sun from BDent are much better. Also while you need low ESR caps, some circuits don't like the ESR to be too low, so try to get replacement caps with similar ESR ratings as the originals.

The experts at BadCaps.net say caps often go bad even without bulging, and some brands and models are more prone to that than others.

Techs often recommend always resoldering the leads on any transformers, even if they look good, because they often crack.
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#9
Quote from atrix415 View Post :
I think I will replaced all the caps. But what are these with caps wrap in heatshrink or something? The caps in blue also looks fine with no leaks, bulging.
I think those are inductors, not caps.
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#10
This is one of the best soldering tutorials I've seen: http://store.curiousinventor.com/..._To_Solder

For desoldering, I can't recommend a desoldering iron with a vacuum bulb strongly enough (available at radio shack). You'll need some fresh solder wick too. You have to be careful about the type of flux / solder / solder wick you use the residue can damage the board over time, you should plan on cleaning the board with 99% rubbingl alcohol when you're done.

As larymoencurly discussed, you absolutely NEED low ESR capacitors which won't be available locally for 99% of people.

The gray glue/goop that's used in certain places on the board can be a little bit of a pain, an assortment of different exacto knife blades will be very useful. It serves as an electrical insulator and mechanical stabilizer, it also effects thermal conduction though not necessarily in a positive manner.

Practice on some old broken electronics you don't care about like an old motherboard or vcr. If you don't have anything to sacrifice, take a trip to goodwill or check the free section on craigslist. These old electronics may use leaded solder and not lead free so the performance will differ.
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Last edited by jkee March 29, 2012 at 07:01 PM
#11
Since I am cheap, I use a 40W Radio Shack soldering iron, desoldering braid, and 60/40 solder when I need to replace a cap.

I have done this on a few motherboards and they work fine even though I do mediocre work.
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#12
I managed to re-solder the caps. I think is the same... I tried HDMI and VGA only the vga is working (I am using for Flight Simulator) on my desktop. It also still show some distortion like interference. I don't know if is due to the cheap surge protector I have or what...
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#13
Quote from jkee View Post :
This is one of the best soldering tutorials I've seen: http://store.curiousinventor.com/..._To_Solder

For desoldering, I can't recommend a desoldering iron with a vacuum bulb strongly enough (available at radio shack). You'll need some fresh solder wick too. You have to be careful about the type of flux / solder / solder wick you use the residue can damage the board over time, you should plan on cleaning the board with 99% rubbingl alcohol when you're done.
Radio Shack also has a $12 model #64-2060 desoldering iron that works well, at least for 2-layer boards:



It helps a lot to wipe the tip frequently, and occasionally a piece of copper or aluminum wire has to be poked into the hole in the tip to unclog it. Steel wire is more likely to damage the iron plating in the hole. This desoldering iron works better if it's modified by wrapping the area above the tip and the metal tube with fiberglass or rock wool insulation so more heat is retained in the tip. People have modified this iron with vacuum pumps or even turned it into a hot air iron by attaching an acquarium pump.
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#14
Quote from atrix415 View Post :
I managed to re-solder the caps. I think is the same... I tried HDMI and VGA only the vga is working (I am using for Flight Simulator) on my desktop. It also still show some distortion like interference. I don't know if is due to the cheap surge protector I have or what...
The interference is more likely from the power supply because all TVs contain a line filter.
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#15
I hate to rain on your parade, but I wouldn't be surprised if these cheap capacitors you picked up at fry's fail within 6-12 months and they or your install job could be responsible for the problems your having. Most power supplies perform badly when you aren't using low ESR caps and the goal of replacing bad caps should be to replace them with a better brand, low esr (slightly lower than the original is ok), and at least as good of a temperature rating as the original. In some cases increasing the voltage of certain caps slightly is also desirable. Bad solder joints could also cause you problems.
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