Jon
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join:2001-01-20
Lisle, IL
1 edit | Good or bad capacitors [RESOLVED]
Do the capacitors in this pick look like they are bad?
The tops are rounded ever so slightly as compared to the others around it.
This is for an Apex LD1919 LCD TV that decided it didn't want to turn on this morning. Searching yielded a lot of people saying these were the problem but I'm not sure. They aren't really "bulging" but aren't flat either. My experience with capacitors is pretty non existent so....
It was destined for the trash anyway so I thought I might take a shot a fixing it and save myself a few hundred bucks. Seems it may be easy enough to take that board off and replace them.
My other question is, Do LCDs hold power like CRTs? I see people talking about getting zapped and would like to avoid that if at all possible.  |
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cowboyro
join:2000-10-11
Shelton, CT
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| Re: Good or bad capacitors
They don't look *bad* but not good either. All capacitors may hold a charge and the power supply will have one that charges to almost 170V, fortunately you don't have the CRT acting as a capacitor and charged to 25-35kV. There will also be capacitors holding high voltage in the light circuit. |
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Jon
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join:2001-01-20
Lisle, IL
| said by cowboyro  :All capacitors may hold a charge and the power supply will have one that charges to almost 170V Would that be dangerous or just hurt?
Is there any way to discharge? |
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pnjunction
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join:2008-01-24
Toronto, ON | reply to Jon
Pretty sure those are bad. They're not supposed to bulge at all, they should actually be slightly concave. |
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cowboyro
join:2000-10-11
Shelton, CT
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| reply to Jon
You can discharge with a 1-10k resistor. Just don't hold it by the terminals  - use some insulated alligator clips.
The charge will not be dangerous in 99.99% of instances, but it will HURT. Trust me  |
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pnjunction
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| reply to cowboyro
said by cowboyro :They don't look *bad* but not good either. All capacitors may hold a charge and the power supply will have one that charges to almost 170V, fortunately you don't have the CRT acting as a capacitor and charged to 25-35kV. There will also be capacitors holding high voltage in the light circuit. Psst..those ones say 25v right on them, they probably have 12-20v maximum. |
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Jon
Premium
join:2001-01-20
Lisle, IL
1 edit | They are 1000uF 25v, whatever that means.
Just want to make sure. Not really worth serious injury. Like I said, experience with capacitors is pretty non existent. Just though it might be a fun project since I'm off this week, it's crappy out and I could save myself a few hundred bucks. |
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Smoove910
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join:2005-08-01
Nampa, ID | reply to Jon
My vote is to replace. They look bad to me |
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Jon
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join:2001-01-20
Lisle, IL
| reply to Jon
Okay next question
Do I just heat the little prongs sticking out to melt the solder and pull them out? Or what the easiest/best way to go about getting the old ones out without damaging the board?
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pnjunction
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Toronto, ON
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| Easiest way would be with a device puller like this with two hot tips. It's designed for surface mount devices but it would work here too. With one solder tip you can only melt one lead at a time. Two soldering guns would work as well.
It can be done with one tip but it's a pain you'll have to try and bend the cap over to pull one heated lead out at a time which might be tricky. A solder-sucker (vacuum pen) might make this a bit easier. |
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TheMG
join:2007-09-04
Edmonton, AB
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| reply to Jon
Head to your nearest Radio Shack or equivalent store, and pickup any of the following if you don't have it already:
-soldering iron (pen style)
-rosin core solder
-desoldering braid
That's all you should need. Maybe a pair of needle-nose pliers could sometimes come in handy too.
Heat up soldering iron, place the desoldering braid on top of the solder connection, then place the iron on top of the braid. The heat will melt the solder and the braid will then "absorb" the solder away from the joint. Continue removing solder until the capacitor can be easily removed.
Do not apply heat to the joint for too long, limit it to a max of 5-10 seconds, and let it cool off before continuing if 5-10 seconds wasn't enough to get the job done.
Soldering in replacement capacitors is fairly straight forward. Watch the polarity, the negative side should match up with a mark on the board, this is VERY important to get right, otherwise the cap will just go "boom" next time you power it up and you'll be at it again. Put capacitor in, trim the leads, apply heat, apply solder until you get a nice concave shaped solder fillet. Remove solder and heat.
When seeking replacement capacitors, you will need low-ESR capacitors of the same capacitance rating (uF) and equal or higher voltage rating.
There are many places online where these capacitors can be obtained. |
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Jon
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join:2001-01-20
Lisle, IL | reply to pnjunction
Yeah I was looking at my soldering gun wonder about that. They're pretty tight to the board so I don't know that there's a lot of room to bend them. I'm headed out to frys in a few so I'll see what they have. |
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Jon
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join:2001-01-20
Lisle, IL | reply to TheMG
Cool thanks for the info. I'll look for the desoldering braid there too.
I already have the pen style iron but what I have on hand is Silver solder, not rosin core. Will the silver solder work or should I get some? |
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cowboyro
join:2000-10-11
Shelton, CT
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| reply to pnjunction
said by pnjunction :Psst..those ones say 25v right on them, they probably have 12-20v maximum. *THOSE* yes - but the ones filtering the rectified AC are a different story - and I was referring to them - there is always a chance of touching them when working on the board. |
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pnjunction
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| reply to Jon
said by Jon :Yeah I was looking at my soldering gun wonder about that. They're pretty tight to the board so I don't know that there's a lot of room to bend them. I'm headed out to frys in a few so I'll see what they have. Yeah looking at the pic they're pretty tight to the board. You'll probably just have to try and remove as much solder as you can with a braid and/or vacuum pen. Then they might come out but they're usually stubborn and stick to the side of the hole, so you can try to heat it up while you pull gently. With them so close to edge of the board you might have room to heat both of the leads at once from the side if necessary. |
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shdesigns
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join:2000-12-01
Stone Mountain, GA | reply to Jon
You will heat one side, tilt the cap a small amount. Heat the other, tilt the other way and repeat until it comes out.
Much easier with solder braid. Be careful, that is a single-sided board. The pads will come off easily when overheated. |
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cowboyro
join:2000-10-11
Shelton, CT
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| reply to Jon
said by Jon :Will the silver solder work or should I get some? Get rosin core. And if you can find the the old lead-based, non ROHS compliant, I suggest that you get it. |
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Jon
Premium
join:2001-01-20
Lisle, IL
| reply to Jon
Went to Frys and Radio shack. They both carry 16,35 & 50v capacitors but neither has 25. WTF? Got the desoldering braid, solder and a new keyboard I've been needing for a while so it wasn't a total waste.
Gonna work on getting the old ones out then go in search of the capacitors. I'd really hate to have to order them and pay $5 or more for shipping on a 90 cent part.  |
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pnjunction
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join:2008-01-24
Toronto, ON | The voltage is just the maximum voltage..the 35v ones would have been fine. |
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Jon
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join:2001-01-20
Lisle, IL
| said by pnjunction :The voltage is just the maximum voltage..the 35v ones would have been fine. Crap really? Ok, I'll run back to radio shack then. |
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